RACHEL MARGARET ASHLEY...RACHEL MARGARET ASHLEY September 2004 i This work contains no material...
Transcript of RACHEL MARGARET ASHLEY...RACHEL MARGARET ASHLEY September 2004 i This work contains no material...
INTEGRATED IRRIGATION AND CANOPY MANAGEMENT STRATEGIES FOR VITIS VINIFERA CV. SHIRAZ.
A thesis submitted in fulfillment of the requirements for the
Degree of Doctor of Philosophy at The University of Adelaide
By
RACHEL MARGARET ASHLEY
September 2004
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This work contains no material which has been accepted for the award of any other degree or diploma in any university or other tertiary institution and, to the best of my knowledge and belief, contains no material previously published or written by another person, except where due reference has been made in the text. I give consent to this copy of my thesis, when deposited in the University Library, being available for loan or photocopying.
____________________ Rachel Margaret Ashley
15 September 2004
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Dedicated to the memory of Eve Cottral.
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SUMMARY
Modern canopy management practices and irrigation strategies have improved the economic
and environmental sustainability of Australia’s wine industry, in terms of increased
production and improved wine quality for minimal production cost and environmental
impact. This study tested the hypothesis that partial rootzone drying (PRD) integrated with
low input, minimal pruning practices can improve sustainability of winegrape production in
warm-climate, irrigated vineyards. The bi-factorial experiment investigated three
conventional pruning practices; hand spur pruning (SPUR), mechanical hedging (MECH)
and minimal pruning (MIN) integrated with standard drip (SD) and PRD irrigation
strategies. The sustainability of winegrape production of field-grown cv. Shiraz grapevines
was determined by examining yield, fruit composition, wine composition and quality, vine
physiology and susceptibility of bunches to Botrytis bunch rot.
Winegrape production was strongly influenced by pruning level and the resultant bunch
number per vine. Increased node retention at pruning of minimal pruned vines resulted in 4-
fold more bunches per vine than spur pruned vines. Mechanical hedged vines had an
intermediate number of bunches per vine. Yield generally reflected the trend in bunch
number per vine. However, minimally pruned and mechanically hedged vines compensated
for greater carbohydrate partitioning between reproductive sinks by producing smaller
bunches with fewer berries per bunch. Partial drying of the grapevine rootzone had a
detrimental effect on yield relative to SD irrigation (18%). The additive effect of SD
combined with light pruning treatments resulted in few statistically significant interactions
for the measured yield components. Berry weight was the only parameter influenced by the
interaction between irrigation and pruning during the three experimental seasons; PRD +
MIN reduced berry weight by 36% compared to SD + SPUR, in response to lower irrigation
inputs and higher bunch number. A 2-fold increase in water use efficiency (tonnes per
megalitre) was found by the reduced irrigation inputs of PRD combined with the high crop
levels of MIN vines compared to SD + SPUR vines.
Fruit and wine composition was also largely unaffected by combined irrigation and pruning
treatments, as a result of the additive effect of PRD and MIN. However, light pruning levels
(MIN and MECH) and their associated small berry size and high bunch exposure, reduced
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pH and increased titratable acidity, and anthocyanin and phenolic concentrations of berry
juice compared to SPUR. Minor pruning level effects on wine composition can be directly
correlated with those observed on fruit composition. PRD had minimal effect on basic fruit
composition but strong effects on wine spectral parameters: density, hue, total anthocyanin
and phenolic concentration and ionised anthocyanin concentration, possibly as a result of co-
pigmentation of anthocyanin compounds with exocarp tannins. Berry size was strongly
correlated with fruit and wine quality. Small berries (i.e. from PRD and MIN) had lower pH
and higher anthocyanin and phenolic concentrations in the juice and produced wine that was
more acidic, brighter and had higher colour density and anthocyanin (total and ionised) and
phenolic concentrations than all other treatments.
Midday and diurnal leaf gas exchange were manipulated by partially drying the rootzone.
PRD reduced midday stomatal conductance, photosynthesis and transpiration compared to
SD. Stomatal limitation on photosynthesis and transpiration was probable, given the strong
positive relationship with stomatal conductance and reduced carbon isotope discrimination
by PRD. Transpiration efficiency was improved for PRD irrigated vines compared to SD
irrigated vines. Leaf water potential and osmotic potential were measured diurnally, in
conjunction with leaf gas exchange to investigate the response of PRD irrigated vines to
increasing vapour pressure deficit. Diurnally, stomatal conductance was reduced by PRD
compared to SD, which maintained leaf water potential, while no osmotic adjustment
occurred. Therefore, PRD irrigation maintained hydraulic water status by hydrating half of
the rootzone, whilst dehydration of the other half of the rootzone resulted in the partial
closure of stomata. Pruning treatment effects on vine physiology were less pronounced.
Minor gas exchange effects showed that pruning level influenced carboxylation efficiency
and not stomatal limitations, as photosynthesis was not directly correlated with stomatal
conductance.
Bunches were least resistant to infection by Botrytis when fully developed and at maximum
maturity. The development of bunches into tighter clusters as berry size increased from
veraison to harvest and the increase in sugar content may have encouraged development of
Botrytis. The distinct bunch architecture resulting from the combined pruning and irrigation
treatments influenced the incidence and severity of Botrytis bunch rot. Light pruning
combined with PRD irrigation produced small, loose bunches in season 2001-02, which
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were less susceptible to Botrytis bunch rot development compared to the large, compact
bunches produced on SD + SPUR vines. However, low bunch numbers and high fruit-set on
MIN and MECH vines in season 2002-03 led to a significant change in bunch architecture.
As a consequence of the increased compactness of bunches in season 2002-03, no pruning
effects on Botrytis development were observed.
Long term economic and environmental sustainability of winegrape production is dependent
on continual improvement in fruit and wine quality, preservation of yield, reduced water and
chemical usage. This study has shown partial drying of the rootzone combined with light
pruning techniques improved yield, fruit and wine composition, water use efficiency and
transpiration efficiency and reduced the incidence and severity of Botrytis bunch rot
compared to SD and severe pruning levels. Therefore, over the three experimental seasons,
PRD combined with minimal pruning was determined as the preferred strategy to enhance
the sustainability of winegrape production of Shiraz cv. in warm-climate, irrigated
vineyards.
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ACKNOWLEDGEMENTS
I am grateful to the Co-operative Research Centre for Viticulture and its associated funding
and research bodies, in particular CSIRO Plant Industry, DPI Victoria, MDBC, The
University of Adelaide and Riverlink, for financial and research support throughout the
duration of my PhD candidature. Also, I am greatly appreciative to my co-supervisors Mr
Peter Clingeleffer, CSIRO PI, Assoc. Prof. Peter Dry, The University of Adelaide and Dr
Bob Emmett, DPI. Special thanks to Peter C for sharing his vast knowledge on practical
viticulture, to Bob E for exposing me to the fascinating world of pathology and teaching me
important mycology techniques and to Peter D for proof-reading my manuscript and
providing important feedback.
I am indebted to my colleagues and friends at CSIRO PI, Horticulture Unit, Merbein for
their continual research support, especially Dr Rob Walker, Dr Nicola Cooley for assistance
with diurnal measurements, Dr Mark Gibberd for help with plant physiology, Dr Paul Petrie
for viticultural advice, Peter Lo Iacono and Sonja Needs for sharing their small-lot wine
making expertise and producing wine each season. Thanks are given to the viticultural team
at DPI; Dr Mark Krstic, Yasmin Chalmers, Glenda Kelly and Lisa Mitchell, for their
continual technical and harvest support. Thankyou to my fellow CRCV PhD students for
sharing their experience and knowledge, particularly Keren Bindon for proofreading my
final draft. A special mention is given to Deakin Estate, Wingara Wine Group Ltd.,
especially Craig Thornton, Assistant Vineyard Manager, Jeff Milne, Vineyard Manager and
Will Davies, Technical Assistant. The experimental site was located in this busy
commercial vineyard and it was with Craig’s continued co-operation, that all experiments
and harvests were successful.
I am truly indebted to my family and friends for their enduring encouragement, support and
love throughout the past 4 years. Without the frequent reassurance and guidance of Mum
and Dad, it is highly unlikely I would have commenced let alone finished my PhD.
Likewise, I am truly thankful for the support and companionship of my dear friends in
Mildura, especially Angelica, Ang, Chelsea, Nicky, Sonja, Nicole and Fiona. Finally, a giant
thank you to my fiancé, Damian, who has encouraged and loved me through the difficult
times of writing-up my thesis.
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LIST OF ABBREVIATIONS
Abbreviation Explanation and Units PRD Partial rootzone drying SD Standard commercial practice drip irrigation SPUR Hand spur pruning MECH Mechanical hedging MIN Minimal pruning PAR Photosynthetically active radiation (µmol.s-1.m-2) DAB Days after budburst DAF Days after flowering DAI Days after irrigation AEDT Australian Eastern Daylight Savings Time LSD Least significant difference θv Volumetric soil-water content (%)
T Temperature (°C) RH Relative humidity (%) VPD Vapour pressure deficit (kPa) SGR Shoot growth rate (cm.day-1) LA Leaf area per vine (m2) LA:F Leaf area to fruit ratio (m2.g.vine-1) WUE Water use efficiency (t.ML-1)
TSS Total soluble solids (°Brix) TA Titratable acidity (g.L-1)
α Percentage of anthocyanin ionisation (%) gs Stomatal conductance (m mol.m-2.s-1)
A Net leaf photosynthesis (µmol.m-2.s-1)
T Net leaf transpiration (µmol.m-2.s-1) A/T Transpiration efficiency (µmol.mmol-1) Ci Internal leaf carbon dioxide concentration (µmol.mol-1)
Ca Atomospheric carbon dioxide concentration (µmol.mol-1) ∆ Carbon isotope discrimination ΨL Leaf water potential (MPa)
ΨS Osmotic potential (MPa) SS Surface sterilisation NS Non-surface sterilisation
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TABLE OF CONTENTS
1 Introduction and literature review........................................................................................................ 1 1.1 Introduction ................................................................................................................................... 1 1.2 Canopy management .................................................................................................................... 1
1.2.1 Winter pruning .................................................................................................................... 3
1.2.2 Pruning systems................................................................................................................... 5
Hand spur pruning............................................................................................................................ 5
Mechanical hedging ............................................................................................................................ 6
Minimal pruning ...............................................................................................................................7
1.3 Irrigation management ................................................................................................................. 9 1.3.1 Partial rootzone drying.....................................................................................................10
1.4 Integration of canopy and irrigation management................................................................ 12 1.5 Conclusion.................................................................................................................................... 13 2 Methodology ................................................................................................................................... 15 2.1 Experimental site......................................................................................................................... 15
2.1.1 Vineyard characteristics ...................................................................................................15
2.1.2 Soil characteristics .............................................................................................................16
2.2 Experimental field trial ............................................................................................................... 17 2.2.1 Irrigation and pruning treatments..................................................................................17
2.2.2 Experimental design .........................................................................................................17
2.2.3 Irrigation scheduling.........................................................................................................19
2.3 Climatic conditions for seasons 2000-2003............................................................................ 24 2.4 Phenological growth dates for seasons 2001-2003 ............................................................... 25
3 Irrigation and pruning effects on yield. ............................................................................................. 27 3.1 Introduction and experimental aims........................................................................................ 27 3.2 Methodology ................................................................................................................................ 28
3.2.1 Canopy development and morphology ........................................................................28
3.2.2 Berry development............................................................................................................29
3.2.3 Harvest components ........................................................................................................30
3.2.4 Statistical analysis ..............................................................................................................30
3.3 Results ........................................................................................................................................... 31 3.3.1 Canopy development and morphology ........................................................................31
3.3.2 Leaf area development.....................................................................................................32
3.3.3 Pruning weights.................................................................................................................34
3.3.4 Berry development............................................................................................................35
3.3.5 Berry maturation ...............................................................................................................35
3.3.6 Bunch number and bunch weight .................................................................................42
3.3.7 Yield.....................................................................................................................................44
3.3.8 Berry weight and berry number .....................................................................................46
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3.3.9 Vine balance.......................................................................................................................48
3.4 Discussion..................................................................................................................................... 49 3.4.1 Pruning and irrigation effects on canopy development.............................................49
3.4.2 Treatment effects on berry development .....................................................................51
3.4.3 Pruning effect on yield components .............................................................................52
3.4.4 PRD influence on yield components ............................................................................53
3.4.5 Treatment effects on vine balance.................................................................................54
3.4.6 Improvements in water use efficiency caused by PRD .............................................55
3.5 Conclusions .................................................................................................................................. 56 4 Irrigation and pruning effects on fruit and wine composition...................................................... 58
4.1 Introduction and experimental aims........................................................................................ 58 4.2 Methodology ................................................................................................................................ 60
4.2.1 Determination of fruit total soluble solids, pH and titratable acidity......................60
4.2.2 Determination of fruit anthocyanin and phenolic concentration............................61
4.2.3 Small-scale wine production ...........................................................................................61
4.2.4 Determination of wine composition.............................................................................62
4.2.5 Statistical analysis ..............................................................................................................63
4.3 Results ........................................................................................................................................... 63 4.3.1 Fruit total soluble solid, pH and titratable acidity results ..........................................63
4.3.2 Fruit anthocyanin and phenolics concentrations and content .................................66
4.3.3 Relationship between anthocyanin concentration and temperature .......................68
4.3.4 Wine pH and titratable acidity results ...........................................................................69
4.3.5 Wine spectral evaluation..................................................................................................71
4.4 Yield and fruit composition correlations ................................................................................ 76 4.5 Yield, fruit and wine composition correlations ..................................................................... 79 4.6 Discussion..................................................................................................................................... 82
4.7.1 Pruning effects on fruit and wine composition...........................................................82
4.7.2 Irrigation effects on fruit and wine composition ........................................................ 83 4.7.3 Irrigation and pruning effects on fruit and wine composition ................................. 85 4.7.4 Influence of yield on fruit and wine composition....................................................... 87 4.7.5 Influence of berry size and TSS on fruit and wine composition ............................. 88
4.7 Conclusions .................................................................................................................................. 89 5 Physiological response to irrigation and pruning treatments ................................................. 91 5.1 Introduction and experimental aims........................................................................................ 91 5.2 Methodology ................................................................................................................................ 93
5.2.1 Midday leaf gas exchange ................................................................................................93
5.2.2 Carbon isotope discrimination .......................................................................................94
5.2.3 PRD vine response to increasing vapour pressure deficit.........................................95
5.2.4 Statistical analysis ..............................................................................................................95
5.3 Results of irrigation and pruning effects on midday leaf gas exchange ............................ 96 5.3.1 Midday leaf gas exchange for 2001-02 and 2002-03 ..................................................96
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5.3.2 Vapour pressure deficit and soil water content.........................................................100
5.3.2 Phenological effect on midday leaf gas exchange.....................................................101
5.4 Irrigation and pruning effects on carbon isotope discrimination ....................................109 5.5 PRD vine physiological response to increasing vapour pressure deficit ........................110
5.5.1 Diurnal increase in vapour pressure deficit................................................................110
5.5.2 Diurnal response of PRD vines ...................................................................................112
5.6 Discussion...................................................................................................................................126 5.6.1 Irrigation effects on leaf gas exchange........................................................................126
5.6.2 Pruning effects on leaf gas exchange ..........................................................................127
5.6.3 Irrigation and pruning effect on leaf gas exchange...................................................127
5.6.4 Leaf gas exchange at different phenological stages ..................................................129
5.6.5 Irrigation and pruning effects on carbon isotope discrimination ..........................131
5.6.6 Diurnal response of PRD vines to increasing vapour pressure deficit.................132
5.6.7 Proposed mechanisms for stomatal closure by PRD...............................................134
5.6.8 Single leaf gas exchange measurements ......................................................................135
5.7 Conclusions ................................................................................................................................135 6 Botrytis bunch rot development and bunch architecture .....................................................137 6.1 Introduction and experimental aims......................................................................................137 6.2 Methodology ..............................................................................................................................139
6.2.1 Isolates of Botrytis cinerea.................................................................................................139
6.2.2 Spore concentration .......................................................................................................140
6.2.3 Botrytis field inoculations at flowering .......................................................................141
6.3.4 Late season Botrytis field inoculations........................................................................141
6.2.5 Bunch architecture..........................................................................................................142
6.2.6 Statistical analysis ............................................................................................................142
6.3 Results .........................................................................................................................................143 6.3.1 Effect of spore concentration on incidence and severity of Botrytis ...................143
6.3.2 Botrytis field inoculations at flowering .......................................................................143
6.3.3 Late season Botrytis field inoculations........................................................................150
6.3.4 Seasonal effects on bunch architecture.......................................................................154
6.3.5 Integrated irrigation and pruning effects on bunch architecture ...........................155
6.3.6 Bunch architecture and Botrytis incidence and severity at harvest .......................158
6.4 Discussion...................................................................................................................................159 6.4.1 Influence of spore concentration on inoculation experiments ..............................159
6.4.2 Botrytis incidence and severity at different bunch development stages...............160
6.4.3 Susceptibility of bunches to late season Botrytis inoculations ...............................161
6.4.4 Influence of irrigation and pruning treatments on Botrytis bunch rot.................162
6.4.5 Irrigation and pruning effects on bunch architecture and Botrytis infection......163
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6.5 Conclusions ................................................................................................................................165 7 General Discussion .............................................................................................................................166
7.1 Introduction to the experiment ..............................................................................................166 7.2 Irrigation effects on sustainability of winegrape production ............................................167 7.3 Pruning effects on sustainability of winegrape production ...............................................169 7.4 Integrated irrigation and pruning effects on sustainability of winegrape production ..171 7.5 Recommendations for the Australian Wine Industry.........................................................173 8 References......................................................................................................................................174
APPENDIX A........................................................................................................................................194 APPENDIX B ........................................................................................................................................195 APPENDIX C ........................................................................................................................................196 APPENDIX D........................................................................................................................................197
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LIST OF FIGURES
Figure 1.1: Response of net photosynthesis of grapevine laminae to sunlight, measured as PAR (Smart 1985)......2 Figure 1.2: Stomatal conductance of Chardonnay (gs) for PRD vines (σ) and non-irrigated vines (□) expressed as a percentage of fully irrigated vines (Dry and Loveys 1999) ................................................................................... 11 Figure 1.3: Net Photosynthesis of Chardonnay (A) for PRD vines (σ) and non-irrigated vines (□) expressed as a percentage of fully irrigated vines (Dry and Loveys 1999) .......................................................................................11 Figure 1.4: Shoot growth rate of Chardonnay (SGR; cm.d-1) for PRD vines (σ) and non-irrigated vines (□) expressed as a percentage of fully irrigated vines (Dry and Loveys 1999)...............................................................12 Figure 2.1: Systematic diagram of alternating PRD irrigation cycles and infrastructure at Deakin Estate; represents non-irrigating drip line and dry rootzone and represents irrigating drip line and associated wet rootzone of grapevine. ................................................................................................................................................18 Figure 2.2: Schematic diagram of experimental field site at Deakin Estate; 2 contiguous latin squares of pruning plots (8 vines each) superimposed on to irrigation rows............................................................................................18 Figure 2.2: Photograph of PRD irrigation infrastructure at Deakin Estate, 2 parallel drip lines irrigate half the rootzone of the vine at a time as indicated by the wet and dry rootzone...................................................................19 Figure 2.4: Figure 2.4: a. Standard drip (SD) volumetric soil-water content of surface (20 cm) and sub-surface soil (50 cm) b. PRD irrigation volumetric soil-water content of surface soil (20-40cm) of north and south side of vine and c. soil-water content of sub-surface soil (50-70cm) of north and south side of vine, as measured by TDR and corresponding irrigation and rainfall events for 2000-01 growing season ................................................................21 Figure 2.5: a. Standard drip (SD) volumetric soil-water content of surface (20 cm) and sub-surface soil (50 cm) b. PRD irrigation volumetric soil-water content of surface soil (20-40cm) of north and south side of vine and c. soil-water content of sub-surface soil (50-70cm) of north and south side of vine, as measured by TDR and corresponding irrigation and rainfall events for 2001-02 growing season. ...............................................................22 Figure 2.6: a. Standard drip (SD) volumetric soil-water content of surface (20 cm) and sub-surface soil (50 cm) b. PRD irrigation volumetric soil-water content of surface soil (20-40cm) of north and south side of vine and c. soil-water content of sub-surface soil (50-70cm) of north and south side of vine, as measured by TDR and corresponding irrigation and rainfall events for 2002-03 growing season ................................................................23 Figure3.1: Pruning treatment effects on shoot growth in season 2000-01; a. shoot length, b. shoots growth rate, c. number of nodes.shoot-1 and d. internode length from budburst to 89 days after budburst (DAB). Significant differences were calculated by Fisher’s least significant difference (LSD) at each time point. LSD is represented by bars and levels of significance are denoted by ***P<0.001, **P<0.01, *P<0.05................................................32 Figure 3.2: a Pruning and b. Irrigation effects on total leaf area development n season 2000-01. Significant differences were calculated by Fisher’s least significant difference (LSD) at each time point. Levels of significance are denoted by ***P<0.001, **P<0.01, *P<0.05, ns = not significant.................................................33 Figure 3.3: Irrigation and pruning effects on berry weight during the maturation period in season 2000-01. Significance of irrigation and pruning interactions were calculated by Fisher’s LSD and are represented on the graph by LSD bars. Levels of significance are denoted by *** P<0.001, ** P<0.01, * P<0.05, ns = not significant. ...................................................................................................................................................................36 Figure 3.4: Irrigation and pruning effects on berry weight during the maturation period in season 2001-02. Significance of irrigation and pruning interactions were calculated by Fisher’s LSD and are represented on the graph by LSD bars. Levels of significance are denoted by *** P<0.001, ** P<0.01, * P<0.05, ns = not significant. ...................................................................................................................................................................36 Figure 3.5: Irrigation and pruning effects on berry weight during the maturation period in season 2002-03. Significance of irrigation and pruning interactions were calculated by Fisher’s LSD and are represented on the
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graph by LSD bars. Levels of significance are denoted by *** P<0.001, ** P<0.01, * P<0.05, ns = not significant. ...................................................................................................................................................................37 Figure 3.6: Integrated irrigation and pruning effects on sugar (TSS) accumulation during the maturation period in season 2000-01. Significance of irrigation and pruning interactions were calculated by Fisher’s LSD and are represented on the graph by LSD bars. Levels of significance are denoted by *** P<0.001, ** P<0.01, * P<0.05, ns = not significant. .....................................................................................................................................................38 Figure 3.7: Integrated irrigation and pruning effects on sugar (TSS) accumulation during the maturation period in season 2001-02. Significance of irrigation and pruning interactions were calculated by Fisher’s LSD and are represented on the graph by LSD bars. Levels of significance are denoted by *** P<0.001, ** P<0.01, * P<0.05, ns = not significant. .....................................................................................................................................................38 Figure 3.8: Integrated irrigation and pruning effects on sugar (TSS) accumulation during the maturation period in season 2002-03. Significance of irrigation and pruning interactions were calculated by Fisher’s LSD and are represented on the graph by LSD bars. Levels of significance are denoted by *** P<0.001, ** P<0.01, * P<0.05, ns = not significant......................................................................................................................................................39 Figure 3.9: Parallel regression model of sugar accumulation in berries on vines with integrated irrigation and pruning treatments for season 2000-01. Refer to Table 3.3 for equations ................................................................40 Figure 3.10: Parallel regression model of sugar accumulation in berries from vines with integrated irrigation and pruning treatments for season 2001-02. Refer to Table 3.3 for equations ................................................................41 Figure 3.11: Common regression model of sugar accumulation in berries from vines with integrated irrigation and pruning treatments for season 2002-03. Refer to Table 3.3 for equations ................................................................41 Figure 5.1: Curvilinear relationship between photosynthesis and stomatal conductance for midday measurements of all treatments (R2 = 0.748), P<0.001 ......................................................................................................................99 Figure 5.2a: Midday stomatal conductance (gs) of SD ( ) and PRD ( ) irrigation treatments measured on six days between veraison and harvest in seasons 2001-02 and 2002-03. Significant differences at each measurement day are represented by ***P>0.001, **P>0.01, *P>0.05, ns = non significant......................................................102 Figure 5.2b: Midday stomatal conductance (gs) of SPUR ( ), MECH ( ) and MIN ( ) pruning treatments measured on six days between veraison and harvest in seasons 2001-02 and 2002-03. Significant differences at each measurement day are represented by ***P>0.001, **P>0.01, *P>0.05, ns = non significant.......................103 Figure 5.2c: Midday stomatal conductance (gs) of integrated irrigation and pruning treatments measured on six days between veraison and harvest in seasons 2001-02 and 2002-03. Significant differences at each measurement day are represented by ***P>0.001, **P>0.01, *P>0.05, ns = non significant......................................................103 Figure 5.3a: Midday leaf photosynthesis (A) of SD ( ) and PRD ( ) irrigation treatments measured on six days between veraison and harvest in seasons 2001-02 and 2002-03. Significant differences at each measurement day are represented by ***P>0.001, **P>0.01, *P>0.05, ns = non significant.............................................................104 Figure 5.3b: Midday leaf photosynthesis (A) of SPUR ( ), MECH ( ) and MIN ( ) pruning treatments measured on six days between veraison and harvest in seasons 2001-02 and 2002-03. Significant differences at each measurement day are represented by ***P>0.001, **P>0.01, *P>0.05, ns = non significant.......................104 Figure 5.3c: Midday leaf photosynthesis (A) of integrated irrigation and pruning treatments measured on six days between veraison and harvest in seasons 2001-02 and 2002-03. Significant differences at each measurement day are represented by ***P>0.001, **P>0.01, *P>0.05, ns = non significant.............................................................105 Figure 5.4a: Midday transpiration (T) of SD ( ) and PRD ( ) irrigation treatments measured on six days between veraison and harvest in seasons 2001-02 and 2002-03. Significant differences at each measurement day are represented by ***P>0.001, **P>0.01, *P>0.05, ns = non significant.............................................................106 Figure 5.4b: Midday transpiration (T) of SPUR ( ), MECH ( ) and MIN ( ) pruning treatments measured on six days between veraison and harvest in seasons 2001-02 and 2002-03. Significant differences at each measurement day are represented by ***P>0.001, **P>0.01, *P>0.05, ns = non significant ...............................106
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Figure 5.4c: Midday transpiration (T) of integrated irrigation and pruning treatments measured on six days between veraison and harvest in seasons 2001-02 and 2002-03. Significant differences at each measurement day are represented by ***P>0.001, **P>0.01, *P>0.05, ns = non significant.............................................................106 Figure 5.5a: Midday internal CO2 concentration (Ci) of SD ( ) and PRD ( ) irrigation treatments measured on six days between veraison and harvest in seasons 2001-02 and 2002-03. Significant differences at each measurement day are represented by ***P>0.001, **P>0.01, *P>0.05, ns = non significant. ..............................107 Figure 5.5b: Midday internal CO2 concentration (Ci) of SPUR ( ), MECH ( ) and MIN ( ) pruning treatments measured on six days between veraison and harvest in seasons 2001-02 and 2002-03. Significant differences at each measurement day are represented by ***P>0.001, **P>0.01, *P>0.05, ns = non significant.......................107 Figure 5.5c: Midday internal CO2 concentration (Ci) of integrated irrigation and pruning treatments measured on six days between veraison and harvest in seasons 2001-02 and 2002-03. Significant differences at each measurement day are represented by ***P>0.001, **P>0.01, *P>0.05, ns = non significant ...............................108 Figure 5.6a: Midday transpiration efficiency (A/T) of SD ( ) and PRD ( ) irrigation treatments measured on six days between veraison and harvest in seasons 2001-02 and 2002-03. Significant differences at each measurement day are represented by ***P>0.001, **P>0.01, *P>0.05, ns = non significant......................................................108 Figure 5.6b: Midday transpiration efficiency (A/T) of SPUR ( ), MECH ( ) and MIN ( ) pruning treatments measured on six days between veraison and harvest in seasons 2001-02 and 2002-03. Significant differences at each measurement day are represented by ***P>0.001, **P>0.01, *P>0.05, ns = non significant.......................109 Figure 5.6c: Midday transpiration efficiency (A/T) of integrated irrigation and pruning treatments measured on six days between veraison and harvest in seasons 2001-02 and 2002-03. Significant differences at each measurement day are represented by ***P>0.001, **P>0.01, *P>0.05, ns = non significant ...............................109 Figure 5.7: Diurnal change in vapour pressure deficit (VPD, kPa) for four diurnal measurement days................111 Figure 5.8a: Diurnal response of PRD on stomatal conductance (gs) on 24 January 2002, ± SEM.......................113 Figure 5.8b: Diurnal response of PRD on photosynthesis (A) on 24 January 2002, ± SEM..................................113 Figure 5.8c: Diurnal response of PRD on transpiration (T) on 24 January 2002, ± SEM......................................114 Figure 5.8d: Diurnal response of PRD on transpiration efficiency (A/T) on 24 January 2002, ± SEM ................114 Figure 5.8e: Diurnal response of PRD on intercellular CO2 partial pressure (Ci) on 24 January 2002, ± SEM....114 Figure 5.8f: Diurnal response of PRD on leaf water potential (ΨL) on 24 January 2002, ± SEM .........................115 Figure 5.8g: Diurnal response of PRD on osmotic potential (ΨS) on 24 January 2002, ± SEM............................115 Figure 5.8h: Diurnal response of PRD on turgor on 24 January 2002, ± SEM.......................................................115 Figure 5.9a: Diurnal response of PRD on stomatal conductance (gs) on 25 January 2002, ± SEM.......................116 Figure 5.9b: Diurnal response of PRD on photosynthesis (A) on 25 January 2002, ± SEM..................................117 Figure 5.9c: Diurnal response of PRD on transpiration (T) on 25 January 2002, ± SEM......................................117 Figure 5.9d: Diurnal response of PRD on transpiration efficiency (A/T) on 25 January 2002, ± SEM.................117 Figure 5.9e: Diurnal response of PRD on intercellular CO2 partial pressure (Ci) on 25 January 2002, ± SEM....118 Figure 5.9f: Diurnal response of PRD on leaf water potential (ΨL) on 25 January 2002, ± SEM .........................118 Figure 5.9g: Diurnal response of PRD on osmotic potential (ΨS) on 25 January 2002, ± SEM............................118
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Figure 5.9h: Diurnal response of PRD on turgor on 25 January 2002, ± SEM.......................................................119 Figure 5.10a: Diurnal response of PRD on stomatal conductance (gs) on 26 February 2002, ± SEM...................120 Figure 5.10b: Diurnal response of PRD on photosynthesis (A) on 26 February 2002, ± SEM..............................120 Figure 5.10c: Diurnal response of PRD on transpiration (T) on 26 February 2002, ± SEM..................................120 Figure 5.10d: Diurnal response of PRD on transpiration efficiency (A/T) on 26 February 2002, ± SEM.............121 Figure 5.10e: Diurnal response of PRD on intercellular CO2 partial pressure (Ci) on 26 February 2002, ± SEM 121 Figure 5.10f: Diurnal response of PRD on leaf water potential (ΨL) on 26 February 2002, ± SEM .....................121 Figure 5.10g: Diurnal response of PRD on osmotic potential (ΨS) on 26 February 2002, ± SEM........................122 Figure 5.10h: Diurnal response of PRD on turgor on 26 February 2002, ± SEM...................................................122 Figure 5.11a: Diurnal response of PRD on stomatal conductance (gs) on 14 February 2003, ± SEM...................123 Figure 5.11b: Diurnal response of PRD on photosynthesis (A) on 14 February 2003, ± SEM..............................123 Figure 5.11c: Diurnal response of PRD on transpiration (T) on 14 February 2003, ± SEM..................................124 Figure 5.11d: Diurnal response of PRD on transpiration efficiency (A/T) on 14 February 2003, ± SEM ............124 Figure 5.11e: Diurnal response of PRD on intercellular CO2 partial pressure (Ci) on 14 February 2002, ± SEM 124 Figure 5.11f: Diurnal response of PRD on leaf water potential (ΨL) on 14 February 2003, ± SEM .....................125 Figure 5.11g: Diurnal response of PRD on osmotic potential (ΨS) on 14 February 2003, ± SEM ........................125 Figure 5.11h: Diurnal response of PRD on turgor on 14 February 2003, ± SEM ..................................................125 Figure 6.1: Mean incidence and severity of Botrytis in seasons 2001-02 and 2002-03 at 4 stages of bunch development; flowering, fruit-set, veraison and harvest. Significant differences between treatment means denoted by different letters as calculated by Fisher’s least significant difference (LSD 5% level) .....................................144 Figure 6.2: Incidence of Botrytis in season 2001-02 of surface (SS) and non-surface sterilised (NS) bunches from integrated irrigation and pruning treatments at 4 phenological stages; flowering, fruit-set, veraison and harvest. Significant differences between phenological stage*treatment*sterilisation were calculated by Fisher’s least significant difference (LSD 5% level). Significance levels are represented by ***P<0.001, **P<0.01, *P<0.05, ns = not significant.........................................................................................................................................................148 Figure 6.3: Incidence of Botrytis in season 2002-03 of surface (SS) and non-surface sterilised (NS) bunches from integrated irrigation and pruning treatments at 4 phenological stages; flowering, fruit-set, veraison and harvest. Significant differences between phenological stage*treatment*sterilisation were calculated by Fisher’s least significant difference (LSD 5% level). Significance levels are represented by ***P<0.001, **P<0.01, *P<0.05, ns = not significant.........................................................................................................................................................148 Figure 6.4: Severity of Botrytis in season 2001-02 of surface (SS) and non-surface sterilised (NS) bunches from integrated irrigation and pruning treatments at 4 phenological stages; flowering, fruit-set, veraison and harvest. Significant differences between phenological stage*treatment*sterilisation were calculated by Fisher’s least significant difference (LSD 5% level). Significance levels are represented by ***P<0.001, **P<0.01, *P<0.05, ns = not significant.........................................................................................................................................................149
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Figure 6.5: Severity of Botrytis in season 2002-03 of surface (SS) and non-surface sterilised (NS) bunches from integrated irrigation and pruning treatments at 4 phenological stages; flowering, fruit-set, veraison and harvest. Significant differences between phenological stage*treatment*sterilisation were calculated by Fisher’s least significant difference (LSD 5% level). Significance levels are represented by ***P<0.001, **P<0.01, *P<0.05, ns = not significant.........................................................................................................................................................150 Figure 6.6: Photograph of representative bunch architecture for each of the combined irrigation and pruning treatments in season 2001-02....................................................................................................................................156 Figure 6.7: Effect of irrigation and pruning treatments at harvest 2001-02 ( ) and 2002-03 ( ) on bunch architectural parameters; a. mean bunch weight, b. berry number vine-1, c. bunch volume, d. maximum width, e. bunch length and f. compactness. Significant differences were calculated by Fisher’s least significant difference (LSD 5% level) and significance levels are indicated by ***P<0.001, **P<0.01, *P<0.05, ns = not significant.157 Figure 6.8 Linear relationships between a. incidence (R2= 0.87, P<0.01) and b. severity (R2= 0.94, P<0.01) of Botrytis and mean bunch weight for integrated irrigation and pruning treatments in 2001-02..............................158 Figure 6.9: Linear relationships between a. incidence (R2= 0.014, P<0.01) and b. severity (R2= 0.009, P<0.01) of Botrytis and mean bunch weight for integrated irrigation and pruning treatments in 2002-03..............................159
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LIST OF TABLES
Table 1.1: Influence of pruning level on mean photosynthetic rate (Pn), stomatal conductance (gs), leaf water potential (ψL), average leaf area and shoot length of Cabernet Sauvignon vines at Mildura, Victoria. Significant difference represented by different letters (P<0.05), adapted from Sommer et al. (1993) .........................................4 Table 1.2: Influence of pruning level on mean yield, bunch number, berry weight, total soluble solid (ºBrix), pH and titratable acidity of Cabernet Sauvignon vines at Mildura, Victoria. Significant difference represented by different letters (P<0.05), adapted from Sommer et al. (1993)....................................................................................4 Table1.3: Comparison of incidence and severity of Botrytis bunch rot on bunches of Chardonnay at Coonawarra from minimally pruned, mechanically hedged and hand pruned vines, adapted from Emmett et al. (1995) ........... 8 Table 2.1: Average monthly climatic data from Mildura Airport: latitude 34°14′S, longitude 142°5′E, 54 years of records (Bureau of Meteorology 2003) ......................................................................................................................15 Table 2.2: Soil characteristic of surface and subsurface soil of Shiraz vineyard, Deakin Estate, Iraak, Victoria: texture (LS= loamy sand, SL= sandy loam, SCL = sandy clay loam), ECe (dS/m), pH, TOC (%), N (%) and P (mg/kg) of surface soil (10-20 cm) and subsurface soil (50-70 cm)..........................................................................17 Table 2.3: Total seasonal irrigation inputs (ML.ha-1) for the three experimental seasons for SD and PRD irrigation treatments at Deakin Estate, Iraak, Victoria...............................................................................................................20 Table 2.4: Mean monthly climatic data from Nangiloc weather station for the 2000-01 growing season...............24 Table 2.5: Mean monthly climatic data from Nangiloc weather station for the 2001-02 growing season...............25 Table 2.6: Mean monthly climatic data from Nangiloc weather station for the 2002-03 growing season...............25 Table 2.7: Calendar date for phenological stages of budburst, flowering, veraison and harvest for Shiraz grapevines at Deakin Estate for seasons 2000-01, 2001-02 and 2002-03 .................................................................26 Table 3.1: Irrigation and pruning effect on total leaf area.vine-1 (LA, m2.vine-1) at maximum canopy development, 22 November 2000-02. * Indicates significance level; *** P<0.001, ** P<0.01, * P<0.05, ns = non significant .34 Table 3.2: Irrigation and pruning effects on pruning weight, cane number.vine-1 and mean cane weight at winter pruning in season 2002-03. * Indicates significance level; *** P<0.001, ** P<0.01, * P<0.05, ns = not significant, different letters denote significant differences between means in each column. ...................................34 Table 3.3: Equations and coefficient of determination (R2) for parallel regression model of sugar accumulation for season’s 2000-01 and 2001-02 and common regression model of sugar accumulation for season 2002-03. Regression model Equations are Total Soluble Solids = constant + slope*Days After Veraison............................40 Table 3.4: Integrated treatment effects on sugar accumulation rate (°Brix.day-1) for seasons 2000-01, 2001-02 and 2002-03. Different letters denote significant differences between seasonal means. *** indicates P<0.001...........42 TABLE 3.5: Bunch number.vine-1 of vines with integrated irrigation and pruning treatments and seasonal means for 2000-01, 2001-02, 2002-03. Different letters denote significant differences between treatment means for each season (column) and across seasons (rows), as calculated by Fisher’s least significant difference (LSD 5% level). Significant differences between treatments are denoted by *** P<0.001, ** P<0.01, * P<0.05, ns= not significant. .....................................................................................................................................................................................43 TABLE 3.6: Bunch weight (g) of vines with integrated irrigation and pruning treatments and seasonal means for 2000-01, 2001-02, 2002-03. Different letters denote significant differences between treatment means for each season (column) and across seasons (rows), as calculated by Fisher’s least significant difference (LSD 5% level). Significant differences between treatments are denoted by *** P<0.001, ** P<0.01, * P<0.05, ns= not significant. .....................................................................................................................................................................................44
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Table 3.7: Coefficient of determination (R2) and statistical significance level (P value) of the negative linear relationship between bunch number vine-1 and bunch weight for all treatments in each season and over the 3 seasons. Significance level is denoted by ** P<0.01, * P<0.05 ...............................................................................44 TABLE 3.8: Yield of vines with integrated irrigation and pruning treatments and seasonal means for 2000-01, 2001-02, 2002-03. Different letters denote significant differences between treatment means for each season (column) and across seasons (rows), as calculated by Fisher’s least significant difference (LSD 5% level). Significant differences between treatments are denoted by *** P<0.001, ** P<0.01, * P<0.05, ns= not significant. .....................................................................................................................................................................................45 TABLE 3.9: Berry weight of vines with integrated irrigation and pruning treatments and seasonal means for 2000-01, 2001-02, 2002-03. Different letters denote significant differences between treatment means for each season (column) and across seasons (rows), as calculated by Fisher’s least significant difference (LSD 5% level). Significant differences between treatments are denoted by *** P<0.001, ** P<0.01, * P<0.05, ns= not significant. .....................................................................................................................................................................................47 TABLE 3.10: Berry number.bunch-1 of vines with integrated irrigation and pruning treatments and seasonal means for 2000-01, 2001-02, 2002-03. Different letters denote significant differences between treatment means for each season (column) and across seasons (rows), as calculated by Fisher’s least significant difference (LSD 5% level). Significant differences between treatments are denoted by *** P<0.001, ** P<0.01, * P<0.05, ns= not significant ....................................................................................................................................................................47 TABLE 3.11: Leaf area: fruit ratio of vines with integrated irrigation and pruning treatments and seasonal means for 2000-01, 2001-02, 2002-03. Different letters denote significant differences between treatment means for each season (column) and across seasons (rows), as calculated by Fisher’s least significant difference (LSD 5% level). Significant differences between treatments are denoted by *** P<0.001, ** P<0.01, * P<0.05, ns= not significant. .....................................................................................................................................................................................48 TABLE 3.12: Water use efficiency of vines with integrated irrigation and pruning treatments and seasonal means for 2000-01, 2001-02, 2002-03. Different letters denote significant differences between treatment means for each season (column) and across seasons (rows), as calculated by Fisher’s least significant difference (LSD 5% level). Significant differences between treatments are denoted by *** P<0.001, ** P<0.01, * P<0.05, ns= not significant. .....................................................................................................................................................................................49 TABLE 4.1: The total soluble solid concentration of berries from vines with integrated irrigation and pruning treatments and seasonal means for 2000-01, 2001-02, 2002-03. Different letters denote significant differences between treatment means for each season (column) and across seasons (rows), as calculated by Fisher’s least significant difference (LSD 5% level). Significant differences between treatments are denoted by *** P<0.001, ** P<0.01, * P<0.05, ns= not significant ...................................................................................................................64 TABLE 4.2: The pH of berries from vines with integrated irrigation and pruning treatments and seasonal means for 2000-01, 2001-02, 2002-03. Different letters denote significant differences between treatment means for each season (column) and across seasons (rows), as calculated by Fisher’s least significant difference (LSD 5% level). Significant differences between treatments are denoted by *** P<0.001, ** P<0.01, * P<0.05, ns= not significant. .....................................................................................................................................................................................65 TABLE 4.3: The titratable acidity of berries from vines with integrated irrigation and pruning treatments and seasonal means for 2000-01, 2001-02, 2002-03. Different letters denote significant differences between treatment means for each season (column) and across seasons (rows), as calculated by Fisher’s least significant difference (LSD 5% level). Significant differences between treatments are denoted by *** P<0.001, ** P<0.01, * P<0.05, ns= not significant.......................................................................................................................................................65 TABLE 4.4: The anthocyanin a. concentration and b. content of berries from vines with integrated irrigation and pruning treatments and seasonal means for 2000-01, 2001-02, 2002-03. Different letters denote significant differences between treatment means for each season (column) and across seasons (rows), as calculated by Fisher’s least significant difference (LSD 5% level). Significant differences between treatments are denoted by *** P<0.001, ** P<0.01, * P<0.05, ns= not significant ............................................................................................67 TABLE 4.5: The a. concentration and b. content of berries from vines with integrated irrigation and pruning treatments and seasonal means for 2000-01, 2001-02, 2002-03. Different letters denote significant differences between treatment means for each season (column) and across seasons (rows), as calculated by Fisher’s least
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significant difference (LSD 5% level). Significant differences between treatments are denoted by *** P<0.001, ** P<0.01, * P<0.05, ns= not significant ...................................................................................................................68 Table 4.6: Correlation coefficients of mean anthocyanin concentration of all treatments with mean daily temperature for the months of December, January and February for the three experimental seasons, n=3. Bold script represents significance at 1% level, P<0.01 .....................................................................................................69 TABLE 4.7: The pH of wine from vines with integrated irrigation and pruning treatments and seasonal means for 2000-01, 2001-02, 2002-03. Different letters denote significant differences between treatment means for each season (column) and across seasons (rows), as calculated by Fisher’s least significant difference (LSD 5% level). Significant differences between treatments are denoted by *** P<0.001, ** P<0.01, * P<0.05, ns= not significant. .....................................................................................................................................................................................70 TABLE 4.8: The titratable acidity of wine from vines with integrated irrigation and pruning treatments and seasonal means for 2000-01, 2001-02, 2002-03. Different letters denote significant differences between treatment means for each season (column) and across seasons (rows), as calculated by Fisher’s least significant difference (LSD 5% level). Significant differences between treatments are denoted by *** P<0.001, ** P<0.01, * P<0.05, ns= not significant.......................................................................................................................................................70 TABLE 4.9: The colour density of wine from integrated irrigation and pruning treatments for season 2000-01, 2001-02, 2002-03 and seasonal means. Different letters denote significant differences between treatment means for each season (column) and across seasons (rows), as calculated by Fisher’s least significant difference (LSD 5% level). Significant differences between treatments denoted by *** P<0.001, ** P<0.01, * P<0.05, ns = non significant ....................................................................................................................................................................71 TABLE 4.10: The colour hue of wine from integrated irrigation and pruning treatments for season 2000-01, 2001-02, 2002-03 and seasonal means. Different letters denote significant differences between treatment means for each season (column) and across seasons (rows), as calculated by Fisher’s least significant difference (LSD 5% level). Significant differences between treatments denoted by *** P<0.001, ** P<0.01, * P<0.05, ns = non significant ....................................................................................................................................................................72 TABLE 4.11: The ionised anthocyanin concentration of wine from integrated irrigation and pruning treatments for season 2000-01, 2001-02, 2002-03 and seasonal means. Different letters denote significant differences between treatment means for each season (column) and across seasons (rows), as calculated by Fisher’s least significant difference (LSD 5% level). Significant differences between treatments denoted by *** P<0.001, ** P<0.01, * P<0.05, ns = non significant.......................................................................................................................73 TABLE 4.12: The total anthocyanin concentration of wine from integrated irrigation and pruning treatments for season 2000-01, 2001-02, 2002-03 and seasonal means. Different letters denote significant differences between treatment means for each season (column) and across seasons (rows), as calculated by Fisher’s least significant difference (LSD 5% level). Significant differences between treatments denoted by *** P<0.001, ** P<0.01, * P<0.05, ns = non significant .......................................................................................................................................74 TABLE 4.13: The degree of ionisation of anthocyanins of wine from integrated irrigation and pruning treatments for season 2000-01, 2001-02, 2002-03 and seasonal means. Different letters denote significant differences between treatment means for each season (column) and across seasons (rows), as calculated by Fisher’s least significant difference (LSD 5% level). Significant differences between treatments denoted by *** P<0.001, ** P<0.01, * P<0.05, ns = non significant.......................................................................................................................75 TABLE 4.14: The total phenolic concentration of wine from integrated irrigation and pruning treatments for season 2000-01, 2001-02, 2002-03 and seasonal means. Different letters denote significant differences between treatment means for each season (column) and across seasons (rows), as calculated by Fisher’s least significant difference (LSD 5% level). Significant differences between treatments denoted by *** P<0.001, ** P<0.01, * P<0.05, ns = non significant .......................................................................................................................................75 Table 4.15: Correlation coefficients of mean yield components [yield, bunch number.vine-1 (Bunch No.), bunch weight (Bunch Wt.), berry number.bunch-1 (Berry No.), leaf area:fruit (LA:F), water use efficiency (WUE)] and fruit composition parameters[total soluble solids (TSS), pH, titratable acidity (TA), anthocyanin concentration (Antho.) and phenolic concentration (Phenol)] for seasons a. 2000-01, b. 2001-02, c. 2002-03, n=6. Bold script represents significance at 5% level.............................................................................................................................77
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Table 4.16: Correlation coefficients of mean yield components [yield, bunch number.vine-1 (Bunch No.), bunch weight (Bunch Wt.), berry number.bunch-1 (Berry No.), leaf area: fruit (LA:F), water use efficiency (WUE)] and fruit composition parameters[total soluble solids (TSS), pH, titratable acidity (TA), anthocyanin concentration (Antho.) and phenolic concentration (Phenol)] for seasons 2000-03, n=18. Bold script represents significance at 5% level.......................................................................................................................................................................78 Table 4.17: Correlation coefficients of mean yield components [yield, bunch number.vine-1 (Bunch No.), bunch weight (Bunch Wt.), berry number.bunch-1 (Berry No.), leaf area:fruit (LA:F), water use efficiency (WUE) and fruit parameters [total soluble solids (TSS), pH, titratable acidity (TA) anthocyanin concentration (Antho.) and phenolic concentration (Phenol.) and wine parameters [tartaric acid addition (TA added), wine pH, wine titratable acidity (TA), colour density, hue, total anthocyanin concentration (Total Antho.), ionised anthocyanin (Ionised Antho.), phenolic concentration (Phenolics), degree of ionisation (alpha)] for season a. 2000-01, b. 2001-02 and 3. 2002-03, n=6. Bold script represents significance at 5% level.................................................................................80 Table 4.18: Correlation coefficients of mean yield components [yield, bunch number.vine-1 (Bunch No.), bunch weight (Bunch Wt.), berry number.bunch-1 (Berry No.), leaf area:fruit (LA:F), water use efficiency (WUE) and fruit parameters [total soluble solids (TSS), pH, titratable acidity (TA) anthocyanin concentration (Antho.) and phenolic concentration (Phenol.) and wine parameters [tartaric acid addition (TA added), wine pH, wine titratable acidity (TA), colour density, hue, total anthocyanin concentration (Total Antho.), ionised anthocyanin (Ionised Antho.), phenolic concentration (Phenolics), degree of ionisation (alpha)] for seasons 2000-03, n=18. Bold script represents significance at 5% level.............................................................................................................................81 Table 5.1: Mean midday leaf stomatal conductance (gs) of vines with integrated irrigation and pruning treatments and seasonal means for 2001-02, 2002-03. Different letters denote significant differences between treatment means for each season (column) and across seasons (rows), as calculated by Fisher’s least significant difference (LSD 5% level). Significant differences between treatments are denoted by *** P<0.001, ** P<0.01, * P<0.05, ns= not significant.......................................................................................................................................................97 Table 5.2: Mean midday photosynthesis (Α) of vines with integrated irrigation and pruning treatments and seasonal means for 2001-02, 2002-03. Different letters denote significant differences between treatment means for each season (column) and across seasons (rows), as calculated by Fisher’s least significant difference (LSD 5% level). Significant differences between treatments are denoted by *** P<0.001, ** P<0.01, * P<0.05, ns= not significant ....................................................................................................................................................................97 Table 5.3: Mean midday Transpiration (Τ) of vines with integrated irrigation and pruning treatments and seasonal means for 2001-02, 2002-03. Different letters denote significant differences between treatment means for each season (column) and across seasons (rows), as calculated by Fisher’s least significant difference (LSD 5% level). Significant differences between treatments are denoted by *** P<0.001, ** P<0.01, * P<0.05, ns= not significant .....................................................................................................................................................................................98 Table 5.4: Mean midday intercellular CO2 concentration (Ci) of vines with integrated irrigation and pruning treatments and seasonal means for 2001-02, 2002-03. Different letters denote significant differences between treatment means for each season (column) and across seasons (rows), as calculated by Fisher’s least significant difference (LSD 5% level). Significant differences between treatments are denoted by *** P<0.001, ** P<0.01, * P<0.05, ns= not significant .........................................................................................................................................98 Table 5.5: Mean midday transpiration efficiency (Α/Τ) of vines with integrated irrigation and pruning treatments and seasonal means for 2001-02, 2002-03. Different letters denote significant differences between treatment means for each season (column) and across seasons (rows), as calculated by Fisher’s least significant difference (LSD 5% level). Significant differences between treatments are denoted by *** P<0.001, ** P<0.01, * P<0.05, ns= not significant.......................................................................................................................................................99 Table 5.6: Midday climatic conditions: temperature (T), relative humidity (RH) and vapour pressure deficit (VPD), number of days after an irrigation event (DAI), corresponding amounts of irrigation water applied to SD and PRD treatments, and number of days after a rainfall event (DAR) and amount of rain (mm) for each of the midday gas exchange measurements........................................................................................................................100 Table 5.7: Midday volumetric soil water content (θv %) of SD and PRD (north and south side of the vine) of surface (20-40 cm) and subsurface soil (50-70 cm) as measured hourly by TDR probes located adjacent to vines. ...................................................................................................................................................................................101
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Table 5.8: Mean Carbon Isotope Discrimination (∆) of vines with integrated irrigation and pruning treatments and seasonal means for 2000-01, 2001-02, 2002-03. Different letters denote significant differences between treatment means for each season (column) and across seasons (rows), as calculated by Fisher’s least significant difference (LSD 5% level). Significant differences between treatments are denoted by *** P<0.001, ** P<0.01, * P<0.05, ns= not significant.....................................................................................................................................................110 Table 5.9: Hourly climatic conditions (Temperature °C, Relative Humidity % and Vapour Pressure Deficit kPa) for each of the diurnal measurement days................................................................................................................111 Table 5.10: Average volumetric soil water contents (θv %) of diurnal measurement days for SD and PRD (north and south side of the vine) of surface (20-40 cm) and subsurface soil (50-70 cm) as measured hourly by TDR probes located adjacent to vines ...............................................................................................................................111 Table 6.1: Incidence and severity of B. cinerea on bunches from all treatments inoculated in the field at flowering in seasons 2001-02 and 2002-03 at spore suspension concentrations of 0, 102 or 104 spores.mL-1. Significant differences calculated by Fisher’s least significant difference (LSD 5% level) and denoted by ***P<0.001, **P<0.01, *P<0.05, ns = non significant .................................................................................................................143 Table 6.2: The mean incidence of Botrytis in season 2001-02 on inoculated and control bunches, surface sterilised (SS) and non-surface sterilised (NS) bunches from integrated irrigation and pruning treatments at 4 stages of bunch development. Significant differences between treatment means are denoted by different letters as calculated by Fisher’s least significant difference (LSD 5% level) and significance levels are indicated by ***P<0.001, **P<0.01, *P<0.05, ns = not significant ............................................................................................145 Table 6.3: The mean incidence of Botrytis in season 2002-03 on inoculated and control bunches, surface sterilised (SS) and non-surface sterilised (NS) bunches from integrated irrigation and pruning treatments at 4 stages of bunch development. Significant differences between treatment means are denoted by different letters as calculated by Fisher’s least significant difference (LSD 5% level) and significance levels are indicated by ***P<0.001, **P<0.01, *P<0.05, ns = not significant ............................................................................................146 Table 6.4: The mean severity of Botrytis in season 2001-02 on inoculated and control bunches, surface sterilised (SS) and non-surface sterilised (NS) bunches from integrated irrigation and pruning treatments at 4 stages of bunch development. Significant differences between treatment means are denoted by different letters as calculated by Fisher’s least significant difference (LSD 5% level) and significance levels are indicated by ***P<0.001, **P<0.01, *P<0.05, ns = not significant ............................................................................................146 Table 6.5: The mean severity of Botrytis in season 2002-03 on inoculated and control bunches, surface sterilised (SS) and non-surface sterilised (NS) bunches from integrated irrigation and pruning treatments at 4 stages of bunch development. Significant differences between treatment means are denoted by different letters as calculated by Fisher’s least significant difference (LSD 5% level) and significance levels are indicated by ***P<0.001, **P<0.01, *P<0.05, ns = not significant ............................................................................................147 Table 6.6: The mean incidence and severity of Botrytis in seasons 2001-02 and 2002-03 on bunches inoculated at flowering, veraison and pre-harvest. Significant differences between treatment means are denoted by different letters as calculated by Fisher’s least significant difference (LSD 5% level) and significance levels are indicated by ***P<0.001, **P<0.01, *P<0.05, ns = not significant .......................................................................................151 Table 6.7: The incidence of Botrytis in seasons 2001-02 and 2002-03 on bunches inoculated at flowering, veraison and pre-harvest. Significant differences between treatment means are denoted by different letters as calculated by Fisher’s least significant difference (LSD 5% level) and significance levels are indicated by ***P<0.001, **P<0.01, *P<0.05, ns = not significant ............................................................................................151 Table 6.8: Severity of Botrytis in seasons 2001-02 and 2002-03 on bunches inoculated at flowering, veraison and pre-harvest. Significant differences between treatment means are denoted by different letters as calculated by Fisher’s least significant difference (LSD 5% level) and significance level are indicated by ***P<0.001, **P<0.01, *P<0.05, ns = not significant ..................................................................................................................152 Table 6.9: The incidence of Botrytis in seasons 2001-02 and 2002-03 on bunches from integrated irrigation and pruning treatments inoculated at flowering, veraison and pre-harvest. Significant differences between treatment means are denoted by different letters as calculated by Fisher’s least significant difference (LSD 5% level) and significance levels are indicated by ***P<0.001, **P<0.01, *P<0.05, ns = not significant ..................................153
xxii
Table 6.10: Severity of Botrytis in seasons 2001-02 and 2002-03 on bunches from integrated irrigation and pruning treatments inoculated at flowering, veraison and pre-harvest. Significant differences between treatment means are denoted by different letters as calculated by Fisher’s least significant difference (LSD 5% level) and significance levels are indicated by ***P<0.001, **P<0.01, *P<0.05, ns = not significant ..................................154 Table 6.11: Bunch architectural parameters, pooled over all treatments, at harvest in seasons 2001-02 and 2002-03. Significant differences between seasons are denoted by different letters as calculated by Fisher’s least significant difference (LSD 5% level) and significance levels are indicated by ***P<0.001, **P<0.01, *P<0.05, ns = not significant....................................................................................................................................................155
Chapter 1: Introduction and Literature Review 1
1 LITERATURE REVIEW
1.1 INTRODUCTION
Modern viticultural practices have been employed by Australia’s wine industry to ensure
sustainable winegrape production. Sustainable winegrape production encompasses
viticultural management, economics and the environment and for this study, is defined as the
consistent production of quantities of high quality grapes sufficient to return a net profit over
an extended period of time with minimal inputs and environmental impact. The long-term
economic and environmental sustainability of winegrape production is dependent on
continual improvement in fruit and wine quality, preservation of yield and reduced water
and chemical inputs. Mechanisation of vineyard processes at harvest and pruning has been
widely accepted by Australia’s wine industry because of reductions in production cost.
Similarly, drip irrigation strategies that trigger water stress responses in grapevines are being
adopted by industry to improve fruit quality and reduce water inputs, particularly on red
winegrape varieties. The adoption of mechanised light pruning practices or induced water
stress irrigation strategies have generally improved production, wine quality and water use
efficiency (Clingeleffer 1993; McCarthy 1996; Dry and Loveys 1998).
Nevertheless, further enhancement of the sustainability of Australia’s wine industry is
essential because of the continual expansion of wine production and subsequent, increased
competition at a global scale. This is particularly important for warm, irrigated regions,
where the bulk of Australia’s winegrapes are sourced. Sustainability, in terms of
production, quality, water use efficiency and disease control may be improved by adopting
an integrated approach to viticulture. In this review, the effects of canopy management and
induced water-stress irrigation strategies on winegrape production, fruit and wine quality,
vine physiology and disease development and the potential of integrated viticultural
management to improve sustainability of winegrape production are discussed.
1.2 CANOPY MANAGEMENT
The microclimate within and directly surrounding a canopy is dependent on the canopy
density (Smart and Robinson 1991). Climatic factors most influenced by canopy density in
Chapter 1: Introduction and Literature Review 2
grapevines are photosynthetic photon flux density, light quality, wind speed, evaporation,
temperature and humidity (Smart et al. 1985). Transmittance of photosynthetically active
radiation through leaves is small (less than 10%) (Pearman 1966). As a result, the light
levels within dense grapevine canopies are very low. Although, interior leaves of dense
canopies have lower photosynthetic rates (Figure 1.1), they still transpire and reduce net
water use efficiency of the grapevine (Escalona et al. 1998).
Consequences of excessive canopy density and vine vigour are reduced yield due to lower
fruit initiation in buds (May 1965) and poor fruit set associated with early bunch stem
necrosis (Jackson 1991). In addition, dense canopies may produce poor quality fruit and
wine. Fruit may have lower sugar, tartaric acid, anthocyanin and phenolic concentrations
and increased berry size, K+ concentrations, pH and malic acid (Morrison 1989; Dokoozlian
and Kliewer 1995). Wines produced from Sauvignon blanc berries from dense canopies
may have an undesirable “herbaceous” character (Allen et al. 1996).
The microclimate of high-density canopies has also been associated with increased disease
development on grapevines because of restricted air movement and increased humidity
(Thomas et al. 1988). High-density canopies may have increased the incidence of Botrytis
bunch rot (Gubler et al. 1987). Disease control may also be difficult because of inefficient
chemical spray penetration within the canopy to infected areas (ie. bunches).
Figure 1.1: The response of net photosynthesis of grapevine laminae to sunlight, measured as photosynthetically active radiation (PAR) (Smart 1985).
Chapter 1: Introduction and Literature Review 3
Canopy management involves a range of viticultural practices that alter the position and
number of shoots, leaves and bunches. The aim of canopy management is to optimise sunlight
interception, photosynthetic capacity and vine microclimate (Smart et al. 1990). The benefits
of canopy management are improved yield and quality (Smart et al. 1990), reduced incidence
of some diseases (Savage and Sall 1984; Emmett et al. 1995) and the facilitation of
mechanisation (Clingeleffer 1983, 1992). Canopy management includes temporary practices
such as winter and summer pruning, leaf removal in the fruiting zone, shoot thinning and
permanent practices such as trellis-training systems. The level of winter pruning can control
shoot number and spacing and thereby control canopy density. Leaf removal may increase
sun exposure in the fruiting zone by reducing leaf area, while shoot thinning may be used to
reduce shoot crowding. Trellis-training systems may increase grapevine growth and capacity
for assimilation (May et al. 1973). Trellis-training systems, such as vertical shoot positioning
(VSP) may also reduce shading within the canopy.
This project focuses on the comparison of different winter pruning techniques for canopy
management, in particular hand spur pruning, mechanical hedging and minimal pruning. The
impact of spur pruning, mechanical hedging and minimal pruning on canopy development,
physiology, productivity, fruit composition and disease development will be discussed.
1.2.1 Winter Pruning
Pruning is the removal of vegetative parts of the vine including shoots, canes and leaves
(Winkler et al. 1974) and is an important cultural practice of the vineyard. Pruning is also the
most expensive and labour consuming aspect of vineyard management after harvest
(Clingeleffer 1992). Pruning practices are chosen in response to vineyard vigour, grapevine
variety, desired wine quality, production costs and climatic conditions of the region.
Pruning aims to select nodes that produce fruitful shoots, regulate shoot number, bunch
number, bunch architecture and improve fruit quality (Tassie and Freeman 1992). Severe
pruning results in vigorous growth to compensate for the reduced number of shoots per vine.
Alternatively, light pruning reduces vegetative growth because of a greater number of shoots
per vine. The level of pruning affects canopy architecture and, ultimately, canopy density.
Light pruning practices result in large open, permanent canopies in contrast to dense canopies
associated to severe pruning levels (Sommer et al. 1993). Although canopy architecture is
Chapter 1: Introduction and Literature Review 4
distinctly different between light and severe pruning levels, Downton and Grant (1992),
Sommer et al. (1993) and Lasko et al. (1996) reported no differences in photosynthetic
capacity when gas exchange and leaf water potential measurements were conducted on
individual, fully sun-exposed leaves (Table 1.1). However, as photosynthesis, stomatal
conductance and leaf water potential vary with leaf size, thickness, age (Syvertsen et al. 1995)
and, in particular, position (Candolfi-Vasconcelos et al. 1994), there are problems associated
with single leaf photosynthetic measurements. Harley and Baldocchi (1995) found that net
photosynthesis was reduced by 31% in shaded leaves compared to fully sun exposed leaves in
a deciduous forest. The rate of development of the canopy, degree of canopy density, ratio of
shaded to exposed leaves and ultimately pruning level can affect net photosynthesis and
stomatal conductance of the grapevine. Lasko et al. (1996) and Poni et al. (2000) showed
canopy net CO2 exchange was significantly higher in minimally pruned vines compared to
hand-pruned vines early in the growing season when their canopies were more advanced. The
difference in canopy net CO2 exchange between light and severe pruned vines was reduced
after flowering as canopy size equilibrated between treatments.
Table 1.1: Influence of pruning level on mean leaf photosynthetic rate (A), leaf stomatal conductance (gs), leaf water potential (ψL), average leaf area and shoot length of Cabernet Sauvignon vines at Mildura, Victoria. Significant difference in means represented by different letters (p<0.05), adapted from Sommer et al. (1993).
Pruning Level A
(µmol m-2s-1)
gs
(mmol m-2s-1) ΨL
(MPa)
Leaf Area
(cm-2)
Shoot Length
(cm)
Light (minimally pruned) 10.6 234 -0.95 65b 39a
Severe (cane pruned) 11.3 245 -0.95 76a 72b
Severe pruning reduces yield because of reduced crop load but bunch weight, berries per
bunch and berry weight are increased (Table 1.2) (Sommer et al. 1993). Light pruning levels
increase yield through increased crop load but bunches are smaller and less compact (Reynold
et al. 1994). The reduced bunch and berry weight may be due to increased partitioning of
carbohydrates between more reproductive sinks.
Table 1.2: Influence of pruning level on mean yield, bunch number, berry weight, total soluble solid (TSS), pH and titratable acidity (TA) of Cabernet Sauvignon at Mildura Victoria. Significant difference in means represented by different letters (p<0.05), adapted from Sommer et al. (1993).
Pruning Level Yield
(t ha-1)
Bunch No.
(vine-1)
Berry Weight
(g)
TSS
(ºBrix)
pH TA
(g L-1)
Light (minimally pruned) 37.7b 585b 0.85a 24.0a 3.42a 5.92
Severe (cane pruned) 24.0a 144a 1.04b 24.6b 3.49b 5.83
Chapter 1: Introduction and Literature Review 5
Sommer et al. (1993) found that the effects of pruning level on fruit composition were
negligible (Table 1.2). However, Bravdo et al. (1985) found that berry maturation was
generally delayed in lightly pruned vines due to the greater crop load. Also, colour may be
enhanced by lighter pruning due to increased exocarp to juice ratio of the smaller berries
(Sommer and Clingeleffer 1993).
1.2.2 Pruning Systems
Hand Spur Pruning
Spur pruned vines are normally bilaterally cordon trained and two-node spurs are retained as
the bearers. Spur pruning suits most grapevine varieties, excluding those with low fruitfulness
at basal nodes (eg. Sultana). At pruning the distal shoot is removed and the proximal shoot is
retained as the new two-node spur. Most spur-pruned vines are classified as severely to
moderately pruned when there are 50 – 180 nodes per vine. Vegetative growth of spur pruned
vines is highly vigorous because of the low shoot density and stimulation of growth near the
pruning cut (Clingeleffer 1992).
Shoots of spur-pruned vines are long with high node number, long internode length and large
leaf size (Clingeleffer and Krake 1992). As a consequence of low shoot number per vine, crop
load is also 1-2 fold lower than lighter pruning systems (Clingeleffer and Sommer 1995).
However, bunch weight, berry weight and berry number per bunch are increased. Reduced
crop load of spur pruned vines increases the rate and degree of sugar maturation in berries
compared to lighter pruned vines (Poni et al. 1994). Other fruit quality parameters including
pH, titratable acidity and K+ concentration are largely unaffected by decreased crop load.
However, improved wine quality (sensory evaluation, colour density and hue) has been
reported for spur-pruned vines (Clingeleffer and Sommer 1995).
The resulting bunch architecture of spur-pruned vines (large, compact bunches) can have
serious implications on disease development (Phillips et al. 1990; Vail and Marois 1991). The
presence of free water is required for the germination of Botrytis cinerea (Jarvis 1980).
Compact bunches exposed to rain may take longer to dry than loose bunches and fully
Chapter 1: Introduction and Literature Review 6
hydrated berries in compact bunches are more likely to rupture (Sall et al. 1982). This
produces a humid microclimate within and around the bunch that can encourage the
development of Botrytis bunch rot (Thomas et al. 1988). Also, the cuticle and epicuticular
wax layers of a grape berry are its main defence against infections by pathogens. Marois et al.
(1985) showed that epicuticular wax plays an important role in the resistance of berries to
Botrytis infection. Damage to the cuticle and epicuticular wax can occur by berry-to-berry
contact within the bunch (Marois 1986). Therefore, compact bunches are expected to have
greater berry contact and, consequently, less resistance to infection.
The facilitation of mechanisation in commercial vineyards, labour shortages and adoption of
lighter pruning techniques for increased production has seen a reduction in hand spur pruning
in recent years in Australia. However, spur pruning is generally still used in small privately-
owned or cool climate vineyards in Australia, which do not use mechanical harvesters as low
bunch density is better suited to hand picking (Clingeleffer and Sommer 1995).
Mechanical Hedging
Mechanical pruning by hedging is a widely accepted cost saving viticultural practice in
Australia, particularly in large vineyards. Hedged vines can be trained to a single wire, narrow
T or 2-vertical wire trellis and pruned to 1 to 6 nodes per bearer depending on the desired
pruning level. Pruning occurs vertically and horizontally to produce a hedge shape, using
circular saws or cutter bars mounted on tractors. Increased vigour can occur in mechanically
hedged vines in cool regions of Australia, as a result of pruning cuts through one-year old
wood (Clingeleffer 1992). Hedged vines have greater canopy density, node number, shoot
number, bunch number and yield per vine compared to hand pruned vines (Smart et al. 1979).
The increase in productivity of mechanically hedged vines generally has not compromised
berry quality in warm climates. Clingeleffer (1993) found no significant differences in berry
and wine quality between hedged, spur and minimally pruned vines but malate and K+
concentrations in the fruit and pH in the wine were slightly higher from hedged vines relative
to the other pruning treatments. High K+ and pH levels in fruit and wine are often associated
large canopies, as a result of excessive bunch shading (Allen et al. 1996).
Chapter 1: Introduction and Literature Review 7
The incidence and severity of Botrytis bunch rot may be increased by the adoption of
mechanical hedging, as a result of increased source inoculum within the shoot zone (Emmett
et al. 1994; Gubler et al. 1987). Large amounts of dead wood and mummified bunches that
can support disease inoculum may be left within the shoot zone of vines after mechanical
hedging of the vines. Also restricted air movement, greater humidity levels and decreased
fungicide spray penetration in dense canopies of hedged vines may encourage disease
development.
Mechanical hedging has been widely adopted in large-scale commercial vineyards as a major
timesaving and cost-efficient canopy management technique. Although, productivity is
increased without reduction to fruit quality compared to more intense pruning techniques,
problems with increased disease incidence may be experienced due to denser canopy structure
and greater levels of background inoculum. Therefore, chemical inputs to the vineyard may
increase to aid disease control. The inherent disease risk associated with mechanical hedging
may be minimised with removal of pruned material from the canopy and vineyard floor.
However, the effectiveness of this method of disease control has not been evaluated in the
literature.
Minimal Pruning
In the minimal pruning system of cordon-trained vines (MPCT) developed at CSIRO Merbein
(Clingeleffer 1983), vines are trained on a high single or two-wire vertical trellis and left
unpruned. Minimal pruning has been successful on a range of grapevine varieties grown on
irrigated vineyards in warm regions (i.e. Sunraysia). Minimal pruning is particularly suitable
for varieties with low basal fruitfulness (Sommer et al. 1995). However, in cool regions and
areas of high shoot vigour (i.e. New Zealand), shoot skirting and summer bunch thinning may
be necessary to reduce bunch number and encourage berry maturation on minimal pruned
vines (Smart and Robinson 1991).
Minimally pruned vines have the capacity to “self-regulate” growth and maintain shape and
productivity by abscission of non-lignified terminal growth during autumn (Possingham et al.
1990). Minimally pruned vines have a 3 to 10-fold increase in shoot number per vine
compared to spur pruned vines. As a result node number per shoot, internode length and leaf
size are reduced. Bunch number and yield are significantly increased but bunches are smaller,
Chapter 1: Introduction and Literature Review 8
less compact and consist of smaller berries compared to those on traditionally hand pruned
vines (Clingeleffer 1983).
The fruiting zone of minimally pruned vines is predominantly on the outside of the canopy
(Emmett et al. 1995) and bunches have greater exposure to the sun. The open canopy
structure, bunch architecture and exposed fruiting zone of minimally pruned vines have been
associated with improved disease control of Botrytis bunch rot and powdery mildew (Kidd
1989; Emmett et al. 1994, 1995). Emmett et al. (1995) found the incidence and severity of
Botrytis bunch rot in Chardonnay from Coonawarra was reduced by 75% and 87%
respectively, compared to spur pruned vines (Table 1.3). Small, loose bunches from
minimally pruned vines may be less inclined to be infected by pathogens because berry cuticle
and epicuticular wax damage from berry to berry contact is lower than in tight, compact
bunches. Also, epicuticular wax production is greater on berries from exposed bunches where
light intensity and temperature are higher (Marois et al. 1986; Percival et al. 1993).
Table 1.3: Comparison of incidence and severity of Botrytis bunch rot on bunches of Chardonnay from minimally pruned, mechanically hedged and hand pruned vines at Coonawarra, adapted from Emmett et al. (1995).
Botrytis bunch rot Minimally Pruned Mechanically Hedged Spur Pruned
Incidence % 18.3 71.2 71.2
Severity % 2.40 18.8 16.5
Minimal pruning does not significantly alter winegrape composition compared to more severe
pruning techniques (Poni et al. 2000). However, sugar maturation may be delayed by minimal
pruning given greater crop level. In conjunction with lower sugar concentrations, titratable
acidity may be slightly lower and pH may be slightly higher in winegrapes from minimal
pruned vines compared to mechanical hedged or spur pruned vines at the same phenological
stage (Clingeleffer 1992). Anthocyanin and phenolic concentrations in berries from minimal
pruned vines may be higher due to an increased exocarp to juice ratio when compared to
berries from spur pruned vines (Sommer and Clingeleffer 1993).
The substantial increase in yield, improved berry colour, disease control and low input costs of
minimal pruned vines compared to mechanically hedged and spur pruned vines makes
minimal pruning favourable to large mechanised vineyards. However, the unknown long-term
repercussions of minimal pruning and delayed ripening of fruit has deterred industry from
Chapter 1: Introduction and Literature Review 9
mass adoption of this pruning technique. Research is being conducted into crop thinning
treatments on minimal pruned vines to increase sugar accumulation, in both warm and cool
winegrape growing regions of Australia (Clingeleffer et al. 2000).
1.3 IRRIGATION MANAGEMENT
Irrigation management of grapevines encompasses a range of different water application
methods including overhead sprinklers, furrow irrigation, under-vine irrigation and drip
irrigation. Irrigation is essential in regions of low rainfall for healthy grapevine development
and increased productivity (Williams and Matthews 1990). However, in recent years the need
to reduce water consumption in irrigated vineyards has risen considerably because of
increased water costs and restrictions on allocated amounts of irrigation water. In addition,
major environmental problems have long been associated with excessive irrigation in
vineyards, such as water logging of the soil, rising ground water table levels and soil
salinisation. Degradation of the soil by water logging and salinisation may lead to decreased
vineyard productivity and wine quality.
Water availability affects vegetative growth indirectly as a result of physiological mechanisms
including leaf water potential, turgor, photosynthesis and transpiration (Bravdo and Hepner
1987). As a result, irrigation management can successfully control vigorous growth in
grapevines, which are known to be sensitive to water stress (Loveys et al. 1998). Grapevines
respond to changes in soil water availability by regulating stomatal conductance to adjust the
rate of transpiration from leaves. Root signals induced by plant growth hormones, such as
abscisic acid (ABA) can influence stomatal conductance (Zhang and Davies 1990; Tardieu et
al. 1992). ABA synthesised in roots exposed to a water deficit can be transported in the xylem
to leaves (Davies and Zhang 1991). In response, stomata reduce their aperture and restrict
water loss by transpiration. Also, ABA has been shown to have an inhibitory effect on leaf
growth (van Volkenburgh and Davies 1983). Therefore, as the concentration of root-sourced
ABA is increased in plants, stomatal conductance and leaf growth rate may be reduced
(Loveys 1984; Zhang and Davies 1990; Tardieu et al. 1992).
Irrigation management of grapevines can involve partially drying the rootzone (PRD) to
stimulate root signals, such as ABA to control shoot growth and transpiration. PRD has been
successfully applied to a range of horticultural crops, such as maize, hot peppers and pear
Chapter 1: Introduction and Literature Review 10
(Kang et al. 1998, 2001, 2003). PRD reduces grapevine vigour while maintaining crop yield
and improving fruit quality and water use efficiency (Dry and Loveys 1998). The potential of
PRD to control vine vigour, improve winegrape composition and water use efficiency is
reviewed below.
1.3.1 Partial Rootzone Drying
Partial rootzone drying (PRD) is an irrigation practice that enables half of the plant root
system to dry out while the other half is irrigated. After a period of time the irrigation is
alternated, so that the roots that were dry are watered and the roots that were hydrated dry out.
The hydrated roots maintain a high plant-water status in the grapevine (shoot water potential
near zero) while the dry roots induce a water-stressed plant response. The concentration of
ABA is increased in the roots from the dry side and has been associated with reduced stomatal
aperture in the leaves. Dry et al. (1996) and Dry and Loveys (1999) found that PRD
significantly reduced stomatal conductance (Figure 1.2), photosynthesis (Figure 1.3), shoot
growth rate (Figure 1.4), leaf area and pruning weights of several grapevine varieties in both
split-pot and field experiments. As a result, grapevine vigour and canopy density are also
reduced (Dry and Loveys 1998). This may have a positive effect on canopy microclimate and
disease control. Although, no reported work has been conducted in this area. Decreased
canopy density may increase air movement and evaporation, thus reduce humidity within the
canopy. The resultant changes in microclimate may be less suitable for the development of
Botrytis bunch rot. The effect of PRD combined with different pruning systems on incidence
and severity of Botrytis bunch rot will be assessed as a component of this study.
Also, an improvement in fruit composition has been attributed to the reduction of canopy
density and increase in berry exocarp to juice ratio by PRD. Cabernet Sauvignon berries had
consistently higher levels of titratable acidity, lower pH and higher concentrations of
anthocyanins, phenols and glycosyl-glucose when vines were irrigated by PRD (Dry et al.
1996; Dry 1997; Loveys et al. 1998). There have been no reported reductions in yield or
berry weight associated with PRD in experimental situations (Dry et al. 1999). However, the
amount of irrigation is halved and thus water use efficiency (WUE), in terms of yield
produced per mega litre of water applied per hectare is improved 2-fold (Düring et al.1996;
Loveys et al. 2000).
Chapter 1: Introduction and Literature Review 11
Improved fruit composition and WUE with no associated yield losses may make PRD more
attractive to the wine industry than other modern irrigation practices which subject vines to
water deficits, such as regulated deficit irrigation (RDI). PRD is also applied to vines
throughout the entire growing season, thus may be less influenced by climatic conditions
compared to deficit irrigation practices applied for short durations at critical phenological
stages. However, PRD does require changes to standard drip irrigation infrastructure
including additional drip lines and taps for swapping irrigations. Also, more research is
required into the length of the drying cycle for sufficient production of root signals and
physiological changes, as it will vary for each vineyard in response to climatic conditions,
grapevine variety and soil type.
Fig. 1.2: Stomatal conductance of Chardonnay (gs; mmol m-2s-1) for PRD vines (▲) and non-irrigated vines (□) expressed as a percentage of fully irrigated vines (Dry and Loveys 1999).
Fig. 1.3: Net Photosynthesis of Chardonnay (Pn; µmol m-2s-1) for PRD vines (▲) and non-irrigated vines (□) expressed as a percentage of fully irrigated vines (Dry and Loveys 1999).
Chapter 1: Introduction and Literature Review 12
Fig. 1.4: Shoot growth rate of Chardonnay (SGR; cm d-1) for PRD vines (▲) and non-irrigated vines (□) expressed as a percentage of fully irrigated vines (Dry and Loveys 1999).
1.4 INTEGRATION OF CANOPY AND IRRIGATION MANAGEMENT
Investigations of integrated canopy and irrigation management are limited to the effects of
crop control and irrigated or non-irrigated treatments on grapevine growth, production and
quality (Freeman et al. 1979; Bravdo et al. 1985; Poni et al. 1994). Grapevine vegetative
growth is increased by the combination of low cropping levels and irrigation (Poni et al.
1994). Crop control practices including thinning and pruning intensity have a greater influence
on bunch number per vine, berry size and yield than increasing available water with irrigation
(Freeman et al. 1979; Bravdo et al. 1985; Poni et al. 1994).
An interaction between crop production and irrigation exists for sugar accumulation in fruit.
Total soluble solids are significantly lower in berries from irrigated vines with high crop load
(Freeman et al. 1980; Bravdo et al. 1985). However, the effects of crop control and irrigation
on other fruit quality parameters (pH, titratable acidity, colour and phenolics) were non-
significant (Freeman et al. 1980; Bravdo et al. 1985).
The consequence of combined canopy and irrigation management on canopy development,
bunch architecture and development of persistent grapevine diseases, such as Botrytis bunch
rot, are as yet unknown.
Chapter 1: Introduction and Literature Review 13
1.5 CONCLUSION
The effects of various canopy or irrigation management techniques on grapevine development,
winegrape production and quality and disease control have been established for both cool and
warm climates. The control of grapevine vigour and reduction of canopy density is required
for the production of high yields and quality winegrapes. To date, this has been achieved in
vineyards by either canopy or irrigation management. Improved canopy microclimate and
productivity has been associated with minimal pruning and partial drying of the rootzone has
improved winegrape composition and wine quality. However, more research is required into
the integration of low-input pruning systems (mechanical hedging and minimal pruning) with
modern irrigation strategies (PRD). Assessment of grapevine development, physiology,
productivity, quality and disease development is essential to develop holistic vineyard
management strategies for improved sustainability and quality.
I have developed the following hypotheses from gaps within the literature that will be
addressed by this project:
• Partial drying of the rootzone integrated with light pruning techniques can improve the
sustainability of winegrape production in warm, irrigated vineyards, in terms of fruit and
wine quality, yield, water-use efficiency and Botrytis bunch rot development.
• Light pruning practices (i.e. minimal pruning) integrated with PRD will increase grape
production by increasing crop level and improve water use efficiency by applying half
the amount of water of standard drip irrigation.
• PRD combined with minimal pruning will improve berry anthocyanin and phenolics
concentration due to an increase in exocarp to juice ratio and reduction in berry size.
• Grapevine vigour and single leaf stomatal conductance will be reduced by the
application of PRD combined with minimal pruning.
• Light pruning practices integrated with PRD irrigation will produce high numbers of
small, loose exposed bunches that will reduce bunch infection and the expression of
Botrytis bunch rot.
Chapter 1: Introduction and Literature Review 14
The objectives of this project were:
• To determine the effects of light pruning practices and PRD irrigation on canopy
development, physiology, productivity, fruit and wine quality, water use efficiency, bunch
architecture and control of Botrytis disease of cv. Shiraz (Vitis vinifera L.).
• To investigate the relationship between yield, fruit composition and wine quality for cv.
Shiraz grown in a warm climate.
• To assess the effects of canopy and bunch architecture on incidence and severity of
Botrytis bunch rot.
• To identify the optimal integrated irrigation and pruning strategy for sustainable
winegrape production in warm-climate, irrigated vineyards.
Chapter 2: Methodology 15
2 METHODOLOGY
2.1 EXPERIMENTAL SITE
2.1.1 Vineyard Characteristics
The experimental site was established on a 5-hectare commercial Shiraz vineyard at Deakin
Estate, Wingara Wine Group Ltd at Iraak in the Sunraysia region of southeast Australia,
latitude 34°25′S, longitude 142°21′E. The climate of the Sunraysia region is semi-arid with
average annual rainfall of 272 mm and mean January temperature of 23.9 °C (Coombe and Dry
1988). Average monthly climatic data from the Mildura Airport (Table 2.1) show a mean
maximum daily temperature range of 15.3°C to 32°C and mean minimum daily temperature
range of 4.3 °C to 16.6 °C. Mean daily relative humidity ranges from 51% to 87% at 0900
AEST and 28% to 57% at 1500 AEST. Median monthly rainfall (mm) ranges from 10.4 mm
to 27.7 mm, with the majority of rainfall occurring during the winter months. The
topographical position of the vineyard is the swale of east-west running sand dunes. The soil-
type is Nookamka sandy loam; consisting of a red-brown to brown sandy loam (0-36 cm),
reddish brown to light brown sandy clay loam with slight lime (36 – 66 cm) and light brown
sandy clay to light clay (66 – 150 cm) (Hubble and Crocker 1941).
Table 2.1: Average monthly climatic data from Mildura Airport: latitude 34°14′S, longitude 142°5′E, 54 years of records (Bureau of Meteorology 2003).
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Year
Daily Mean Temperatures °C
Maximum 32.0 31.5 28.2 23.3 18.9 15.9 15.3 17.1 20.2 23.7 27.2 30.0 23.6 Minimum 16.6 16.4 13.8 10.1 7.5 5.2 4.3 5.3 7.3 9.8 12.3 14.7 10.3 Relative Humidity % 0900 EST 53 57 61 70 83 88 87 80 69 58 54 51 67 1500 EST 28 31 34 41 51 57 55 48 41 36 31 28 40 Rainfall mm Mean 21.8 21.5 18.8 19.3 27.3 23.1 26.9 27.5 28.8 31.5 24.5 22.2 293 Median 13.0 10.6 10.4 13.2 22.9 16.3 27.7 26.1 25.5 22.4 18.1 12.7 287
Chapter 2: Methodology 16
Vitis vinifera cv Shiraz grafted on Schwarzmann (V. riparia x V. rupestris) rootstock was
planted in 1994, at a vine spacing of 2.4 m and row spacing of 3.0 m, in an east-west
orientation. Vine planting density is 1389 vines per hectare. The vines were trained to 4
cordons on a two-wire vertical trellis, mechanically hedged and drip irrigated. Partial rootzone
drying irrigation was applied to every third row in 1997. Six rows each of drip irrigated and
PRD irrigated vines were randomly selected from the 46 available rows for this field
experiment in 2000. Three conventional canopy management practices were applied to vines
in the selected irrigation rows in July 2000 to assess the effects of integrated viticulture on
grape production, fruit composition, disease control and water use efficiency.
2.1.2 Soil Characteristics
Soil physical and chemical parameters were measured on surface (10-20 cm) and sub-surface
(50-70cm) samples collected 20 cm from the base of a vine, every 10 metres in experimental
rows. Soil samples were air-dried, 2mm sieved and the following parameters were measured:
soil texture, electrical conductivity, pH, total organic carbon, total nitrogen and phosphorus.
Soil texture was determined by hand feel and classified as loamy sand, sandy loam, light sandy
clay loam, sandy clay loam, clay loam sand or light clay. Electrical conductivity (ECe) of a
soil suspension was used to estimate the concentration of soluble salts in the soil and pH
indicated the intensity of acidity of the soil. ECe and pH were determined on a 1:5 soil/H2O
extract as described by Rayment and Higgins (1992). Total organic carbon (TOC) and total
Nitrogen (N) in the soil was determined by combustion in a high frequency induction furnace
and detection by mass spectrometry. Soil phosphorus (P) content was determined using a
1:100 extraction with 0.5M sodium bicarbonate (NaHCO3) followed by colorimetric
determination.
Soil texture of the surface soil (10-20 cm) ranged from loamy sand to sandy loam and light
sandy clay loam to sandy loam clay in the subsurface soil (50-70 cm). Electrical conductivity
increased significantly with depth by 0.32 dS/m (Table 2.2). However, levels fell below the
recommended salinity threshold for grapes of 1.5 dS/m, at which level growth and yield
declines may be expected. An increase (3%) in soil alkalinity and total organic carbon content
(41%) also occurred with depth. Total nitrogen and phosphorus content were greater in the
surface soil than the subsurface soil, by 2-fold and 11-fold, respectively. The higher levels of
Chapter 2: Methodology 17
phosphorus content in the surface soil can be attributed to regular granular phosphate fertilizer
applications along the irrigation rows.
Table 2.2: Soil characteristics of surface and subsurface soil of Shiraz vineyard, Deakin Estate, Iraak, Victoria: texture (LS= loamy sand, SL= sandy loam, SCL = sandy clay loam), ECe (dS/m), pH, TOC (%), N (%) and P (mg/kg) of surface soil (10-20 cm) and subsurface soil (50-70 cm). Depth cm Texture ECe pH TOC % N % P mg/kg 10-20 LS-SL 0.43a 7.67a 0.33a 0.02b 17.1 50-70 LSCL-SLC 0.75b 7.90b 0.56b 0.01a 1.5 LSD (5% level) 0.111 0.095 0.080 0.002 15.3
2.2 EXPERIMENTAL FIELD TRIAL
2.2.1 Irrigation and Pruning Treatments
The standard drip (SD) irrigation treatment consisted of a single drip-line; 19 mm diameter,
drip spacing of 700 mm and average seasonal output of 5.4 ML/ha. The partial rootzone
drying (PRD) irrigation treatment applied irrigation water to half of the vine rootzone at a time
by using two parallel drip lines of 19 mm diameter with 4 L hr-1 emitters, spaced at 450 mm on
alternate (east or west) sides of the vine (Figure 2.1 and 2.3). The average seasonal output of
PRD was 3.0 ML/ha. Three conventional pruning techniques of different pruning levels were
superimposed on the irrigation treatments. The pruning treatments were hand spur pruning
(SPUR), mechanical hedging (MECH) and minimal pruning (MIN). Hand spur pruned vines
had 30 spurs (ten spurs on upper cordons and five spurs on the lower cordons) with two buds
per spur. Mechanical hedged vines were pruned by tractor with vertical and horizontal cutter
bars at a distance of 200 mm from the trellis wire, resulting in an approximate bud number
vine-1 of 150. Minimally pruned vines were skirted at a height of 1 m from ground level to
reduce disease incidence by cane contact with soil, approximate bud number vine-1 was >300.
2.2.2 Experimental Design
The experimental design was a 6 x 6 row-column design. Six irrigation rows (3 SD + 3 PRD)
were randomly selected and divided into six pruning plots, aligned in columns. The three
pruning treatments were assigned to the SD and PRD irrigation rows in two contiguous Latin
Chapter 2: Methodology 18
Squares (Figure 2.2). Thus the combined irrigation and pruning treatment plots were
replicated six times in the vineyard. The pruning plots consisted of eight vines each and n=288.
The two outer vines of each plot served as buffer vines, the two central vines were chosen for
all harvest measurements and remaining vines were used for physiology and pathology
experiments. The Latin Square design was maintained to enable testing (and elimination) of
any column effects along the rows, as well as the orthogonal estimation of the irrigation
effects, pruning effects and also treatment interactions.
Figure 2.1: Systematic diagram of alternating PRD irrigation cycles and infrastructure at Deakin Estate; represents non-irrigating drip line and dry rootzone and represents irrigating drip line and associated wet rootzone of grapevine.
Row Irrigation Plot 1 Plot 2 Plot 3 Plot 4 Plot 5 Plot 6 42 SD Mech Min Spur Spur Min Mech 63 SD Spur Mech Min Mech Spur Min 75 SD Min Spur Mech Min Mech Spur 49 PRD Spur Min Mech Mech Min Spur 61 PRD Mech Spur Min Spur Mech Min 73 PRD Min Mech Spur Min Spur Mech
Figure 2.2: Schematic diagram of experimental field site at Deakin Estate; 2 contiguous latin squares of pruning plots (8 vines each) superimposed on to irrigation rows.
Dry rootzone
Wet rootzone
Grapevine
Dry rootzone
Wet rootzone
Grapevine
North drip line
South drip line
North drip line
South drip line
iIrr gation Cycle 1
Irrigation Cycle 2
Chapter 2: Methodology 19
Southern Drip lineDry Rootzone
Northern Drip line Wet Rootzone
Figure 2.3: Photograph of PRD irrigation infrastructure at Deakin Estate, 2 parallel drip lines irrigate half the rootzone of the vine at a time as indicated by the wet and dry rootzone.
2.2.3 Irrigation Scheduling
Irrigation scheduling was monitored by time domain reflectometry (TDR) using CS615 water
content reflectometers (Campbell Scientific Inc., Logan, Utah). The reflectometers measured
volumetric soil-water content (θv). The volumetric soil-water content was derived from the
effect of changing dielectric constant on electromagnetic waves propagating along a wave-
guide. The water content reflectometers consisted of two parallel 30 cm steel rods (wave-
guide) and were buried at the base of SD and PRD irrigated vines at two soil depth ranges (20-
40 cm and 50-70 cm) to encompass the rooting depth of 20 to 70cm. θv was logged every hour
by CR10X data loggers (Campbell Scientific Inc., Logan, Utah). Irrigation water was applied
when θv reached 23%. Frequency of irrigation events was dependent on plant-water use and
evapotranspiration. PRD was applied to the vines on an alternate cycle; thus each irrigation
Chapter 2: Methodology 20
event was swapped between the north and south drip lines. This cycle was chosen to ensure a
dry rootzone on one side of the vine without having detrimental effects on root health, given
the low water-holding capacity of the sandy loam soil and high mean summer temperatures of
the region.
Soil-water content, irrigation water input and rainfall input for SD and PRD treatments for
each growing seasons are presented in Figure 2.4a, b and c (2000-01), Figure 2.5a, b and c
(2001-02) and Figure 2.6a, b and c (2002-03). Irrigations began in October or early
November, depending on the growing season and winter rainfall. Irrigation began on the 9
November in 2000, as spring rains were relatively high in October. However, irrigations
started a month earlier in 2001 and 2002, on 8 and 9 October respectively, because of the lack
of winter and spring rainfall. Irrigation frequency was four days when water demands were
greatest (January and February) and approximately 18-21 mm of water per irrigation event was
applied for SD and 11-13.8 mm for PRD treatments, depending on daily plant water use.
The total amount of irrigation water applied for SD and PRD was monitored by inline flow
meters, located at the lateral valve in two of the three experimental rows for each treatment.
Total seasonal irrigation amounts per hectare were calculated from average flow meter
readings for the three experimental growing seasons. Seasonal irrigation inputs ranged from
5.0 to 5.4 ML ha-1 for SD and 2.5 to 3.1 ML ha-1 for PRD irrigation and are presented in (Table
2.3).
Table 2.3: Total seasonal irrigation inputs (ML ha-1) for the three experimental seasons for SD and PRD irrigation treatments at Deakin Estate, Iraak, Victoria.
Irrigation Treatment 2000-01 2001-02 2002-03
Standard Drip 5.44 5.07 5.21 Partial Rootzone Drying 3.13 2.50 2.93
Chapter 2: Methodology 21
0.00
0.10
0.20
0.30
0.40
0.50
0.60
0.70
0.80
Soi
l Wat
er C
onte
nt
0.0
10.0
20.0
30.0
40.0
50.0
60.0
70.0
Input Water m
m
a. RainfallIrrigationSD 20 cmSD 50 cm
18/10 1/11 15/11 29/11 13/12 27/12 10/1 24/1 7/2 21/2 7/3
Date
0.00
0.10
0.20
0.30
0.40
0.50
0.60
0.70
0.80
18/10 1/11 15/11 29/11 13/12 27/12 10/1 24/1 7/2 21/2 7/3
Date
Soi
l Wat
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onte
nt
0.0
10.0
20.0
30.0
40.0
50.0
60.0
70.0
Input Water m
m
RainfallPRD irrig northPRD irrig southPRD 20cm northPRD 20cm south
b.
0.00
0.10
0.20
0.30
0.40
0.50
0.60
0.70
0.80
18/10 1/11 15/11 29/11 13/12 27/12 10/1 24/1 7/2 21/2 7/3
Date
Soi
l Wat
er C
onte
nt
0.0
10.0
20.0
30.0
40.0
50.0
60.0
70.0
Input Water m
m
RainfallPRD irrig northPRD irrig southPRD 50cm north PRD 50cm south
c.
Figure 2.4: a. Standard drip (SD) volumetric soil-water content of surface (20 cm) and sub-surface soil (50 cm) b. PRD irrigation volumetric soil-water content of surface soil (20-40cm) of north and south side of vine and c. soil-water content of sub-surface soil (50-70cm) of north and south side of vine, as measured by TDR and corresponding irrigation and rainfall events for 2000-01 growing season.
Chapter 2: Methodology 22
0.00
0.10
0.20
0.30
0.40
0.50
0.60
0.70
0.80
Soil
Wat
er C
onte
nt
0.0
10.0
20.0
30.0
40.0
50.0
60.0
70.0
Input Water m
m
1/10 15/10 29/10 12/11 26/11 10/12 24/12 7/1 21/1 4/2 18/2 4/3
Date
RainIrrig SDSD 20cmSD 50 cm
0.00
0.10
0.20
0.30
0.40
0.50
0.60
0.70
0.80
1/10 15/10 29/10 12/11 26/11 10/12 24/12 7/1 21/1 4/2 18/2 4/3
Date
Soi
l Wat
er C
onte
nt
0.0
10.0
20.0
30.0
40.0
50.0
60.0
70.0
Input Water m
m
RainIrrig NIrrig SPRD 20cm northPRD 20cm south
0.00
0.10
0.20
0.30
0.40
0.50
0.60
0.70
0.80
1/10 15/10 29/10 12/11 26/11 10/12 24/12 7/1 21/1 4/2 18/2 4/3
Date
Soi
l Wat
er C
onte
nt
0.0
10.0
20.0
30.0
40.0
50.0
60.0
70.0
Input Water m
m
RainIrrig NIrrig SPRD 50cm northPRD 50cm south
c.
b.
a.
Figure 2.5: a. Standard drip (SD) volumetric soil-water content of surface (20 cm) and sub-surface soil (50 cm) b. PRD irrigation volumetric soil-water content of surface soil (20-40cm) of north and south side of vine and c. soil-water content of sub-surface soil (50-70cm) of north and south side of vine, as measured by TDR and corresponding irrigation and rainfall events for 2001-02 growing season.
Chapter 2: Methodology 23
0.00
0.10
0.20
0.30
0.40
0.50
0.60
0.70
0.80
1/10 15/10 29/10 12/11 26/11 10/12 24/12 7/1 21/1 4/2 18/2 4/3
Date
Figure 2.6: a. Standard drip (SD) volumetric soil-water content of surface (20 cm) and sub-surface soil (50 cm) b. PRD irrigation volumetric soil-water content of surface soil (20-40cm) of north and south side of vine and c. soil-water content of sub-surface soil (50-70cm) of north and south side of vine, as measured by TDR and corresponding irrigation and rainfall events for 2002-03 growing season.
Soi
l Wat
er C
onte
nt
0.0
10.0
20.0
30.0
40.0
50.0
60.0
70.0
Input Water m
mRain
Irrig SD
SD 20cm
SD 50 cm
0.00
0.10
0.20
0.30
0.40
0.50
0.60
0.70
0.80
1/10 15/10 29/10 12/11 26/11 10/12 24/12 7/1 21/1 4/2 18/2 4/3
Date
Soi
l Wat
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onte
nt
0.0
10.0
20.0
30.0
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Input Water m
m
RainIrrig NIrrig SPRD 20cm northPRD 20cm south
0.00
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1/10 15/10 29/10 12/11 26/11 10/12 24/12 7/1 21/1 4/2 18/2 4/3
Date
Soi
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onte
nt
0.0
10.0
20.0
30.0
40.0
50.0
60.0
70.0
Input Water m
m
RainIrrig NIrrig SPRD 50cm northPRD 50cm south
a.
b.
c.
Chapter 2: Methodology 24
2.3 CLIMATIC CONDITIONS FOR SEASONS 2000-2003
Climatic data was collected daily (0900 AEST) from a weather station located 5 km southeast
of the vineyard at Nangiloc. Climatic parameters included mean daily temperature (minimum
and maximum), relative humidity (minimum and maximum), rainfall (previous 24 hours),
mean daily evaporation and mean daily sunshine hours. Monthly means are presented in
Tables 2.4, 2.5 and 2.6 for the three grape-growing seasons when experiments were conducted.
The three experimental growing seasons deviated from 50-year season averages with higher
summer temperatures in 2000-01, lower summer temperatures in 2001-02 and below average
annual rainfall in 2001-02 and 2002-03. Mean maximum temperature for January 2001 (36°C)
was 14% greater than the 50 year mean maximum January temperature (32°C) for the region
(Bureau of Meteorology 2003). The following season was milder than the 50-year average
with lower mean maximum and minimum temperatures from October 2001 to February 2002.
Drought conditions prevailed in the second and third season; the total annual rainfall was 44%
and 36% lower than the 50-year annual rainfall average in 2001-02 and 2002-03, respectively.
The majority of rainfall occurred during the late winter to early spring months in 2000-01 and
2001-02, however two large rainfall events in December and February dominated the annual
rainfall in 2002-03. Relative humidity was consistent throughout the three growing seasons
with maximal values recorded throughout the winter months. Daily sunshine hours were
greatest during the summer months and minimal variation was recorded between growing
seasons from 2000-2003.
Table 2.4: Mean monthly climatic data from Nangiloc weather station for the 2000-01 growing season.
2000-01 May Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr
Daily Mean Temperatures °C Maximum 17.6 15.6 15.3 17.0 21.3 23.0 29.6 32.2 36.3 33.9 27.8 23.8 Minimum 5.3 4.9 4.5 4.7 8.4 8.6 14.9 15.1 19.1 19.2 11.8 8.7 Relative Humidity % Maximum 98.5 97.5 98.6 97.2 96.5 91.0 88.4 73.3 71.2 74.6 84.2 88.5 Minimum 50.5 55.8 56.6 45.5 41.4 34.8 31.9 19.9 19.5 27.7 28.4 33.5 Rainfall mm Total 13.4 8.6 23.2 22.4 35.2 40.6 14.2 15.8 1.4 30.0 19.2 3.4 Evaporation mm (24 hrs) Mean 1.5 1.2 1.3 1.8 2.7 3.7 4.8 6.2 6.6 5.2 4.1 2.8 Daily Sun Hours Mean 6.9 5.2 6.2 6.6 7.5 8.9 10.1 9.8 11.4 9.7 10.0 8.4
Chapter 2: Methodology 25
Table 2.5: Mean monthly climatic data from Nangiloc weather station for the 2001-02 growing season
2001-02 May Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr
Daily Mean Temperatures °C Maximum 19.7 17.0 14.6 18.0 22.2 22.8 26.3 28.2 31.9 30.6 28.5 26.3 Minimum 6.5 5.4 4.3 6.1 9.3 8.5 10.6 11.9 14.7 14.2 12.4 10.4 Relative Humidity % Maximum 95.9 77.5 99.8 90.7 89.9 88.9 88.0 84.9 67.1 73.8 85.5 91.7 Minimum 46.1 60.0 65.6 43.9 37.1 32.8 25.6 23.2 16.0 22.2 30.0 32.7 Rainfall mm Total 0.0 2.2 6.6 35.8 42.8 22.8 1.6 3.2 0.2 8.2 22.2 18.6 Evaporation mm (24 hrs) Mean 1.7 1.2 1.1 1.4 2.7 3.5 4.6 4.9 6.2 5.4 4.3 2.9 Daily Sun Hours Mean 6.4 6.0 5.4 7.1 7.4 8.9 10.1 9.8 11.1 11.4 10.6 9.1
Table 2.6: Mean monthly climatic data from Nangiloc weather station for the 2002-03 growing season.
2002-03 May Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr
Daily Mean Temperatures °C Maximum 20.8 16.9 17.4 18.0 22.0 25.0 30.2 31.7 33.7 33.2 24.5 25.9 Minimum 7.0 5.1 4.1 3.6 6.9 8.0 12.8 14.6 16.6 16.2 10.9 9.5 Relative Humidity % Maximum 91.8 99.8 94.8 91.4 88.0 88.2 78.7 73.1 69.7 79.5 89.0 84.8 Minimum 39.6 50.1 44.2 31.9 30.8 26.0 21.0 19.5 20.0 23.6 28.3 36.4 Rainfall mm Total 16.2 13.0 4.8 15.6 7.0 7.0 20.0 58.2 0.2 45.0 0.0 1.2 Evaporation mm (24 hrs) Mean 1.8 1.2 1.4 2.3 3.1 4.5 5.2 6.0 6.7 5.6 4.2 2.9 Daily Sun Hours Mean 6.9 6.2 7.3 8.6 9.5 10.0 9.9 10.6 11.8 9.6 9.9 8.7
2.4 PHENOLOGICAL GROWTH DATES FOR SEASONS 2001-2003
Important phenological dates of grapevine development were recorded for the three
experimental seasons and are presented in Table 2.7. Budburst occurred in the month of
September of each experimental season, however it became progressively later in the month
over the three seasons. Similarly, flowering, as determined by 80% capfall, became later in the
calendar year over the duration of the study. Veraison was early in the first experimental year
compared to the other two seasons, which reflects the early flowering date for that season, as a
Chapter 2: Methodology 26
result of relatively high temperatures at the end of October and beginning of November in
2000. Harvest occurred in the 2001 vintage on March 6 for all irrigation and pruning
treatments. However, irrigation and pruning treatments were harvested by berry maturity level
in subsequent seasons. The range in harvest date of the six treatments was approximately 11 to
14 days in the latter two seasons.
Table 2.7: Calendar date for phenological stages of budburst, flowering, veraison and harvest for Shiraz grapevines at Deakin Estate for seasons 2000-01, 2001-02 and 2002-03.
Phenological Stage Season 2000-01 Season 2001-02 Season 2002-03 Budburst 12/9/00 15/9/01 23/9/02 Flowering 4/11/00 15/11/01 18/11/02 Veraison 12/1/01 30/1/01 21/1/03 Harvest 6/3/01 28/2-14/3/01 27/2-10/3/03
Chapter 3: Irrigation and pruning effects on yield 27
3 IRRIGATION AND PRUNING EFFECTS ON YIELD
3.1 INTRODUCTION AND EXPERIMENTAL AIMS
Sustainable winegrape production is dependent on the carbon balance between vegetative
and reproductive development. Vine balance is achieved when “vegetative vigour and fruit
load are in equilibrium and consistent with high fruit quality” (Gladstones 1992). Excessive
shoot vigour and foliage growth alters the “source-sink” relationship. This can have
detrimental effects on yield and fruit quality because of increased canopy density and fruit
shading (May 1965; Morrison 1989; Reynolds and Wardle 1989; Dokoolizan and Kliewer
1995; Allen et al. 1996). On the other hand, excessively heavy cropping is known to limit
canopy growth and fruit quality (Bravdo et al. 1985; Smart and Robinson 1991). The
vegetative to reproductive ratio is used to measure vine balance and varies with canopy
management (pruning, trellising, shoot positioning) and irrigation (water supply, timing,
scheduling).
The level of winter pruning and number of nodes retained per vine affects the source-sink
ratio and carbohydrate partitioning. Severe levels of pruning, such as spur pruning can
increase shoot vigour (Smart et al. 1990; Downton and Grant 1992). Shoot vigour is
increased by severe pruning, as a result of fewer shoots per vine and subsequently, reduced
competition for carbohydrates by shoot apices. Also, fewer nodes retained by severe
pruning leads to lower crop levels because of reduced bunch numbers per vine (Clingeleffer
1993; Sommer et al. 1993; Lasko et al. 1996; Poni et al. 2000). In contrast, light pruning
levels, such as mechanical hedging and minimal pruning retain a greater node number at
pruning than hand spur pruning. Carbohydrate competition and partitioning is increased for
both vegetative and reproductive growth in mechanically hedged and minimally pruned
vines. As a result shoot vigour, bunch weight and berry weight is reduced but yield is
maintained by increased crop level (Clingeleffer 1984).
Irrigation is used to successfully increase productivity of grape vines in areas of low rainfall,
however irrigation can also be used as a management tool to control shoot vigour. The
imposition of regulated water deficits at crucial growth stages can inhibit shoot growth (van
Chapter 3: Irrigation and pruning effects on yield 28
Zyl 1984; Williams and Grimes 1987) and leaf area (Williams and Matthews 1990), as well
as manipulate berry size (Goodwin and Jerie 1992; Poni et al. 1993; McCarthy 1997a). An
alternative to deficit irrigation is partial rootzone drying (PRD), where a drought response is
induced in the grapevine by drying half the rootzone, while plant water status is maintained
by irrigating the other half of the rootzone. PRD has been shown to reduce grapevine shoot
vigour and subsequently canopy density but crop load is relatively unaffected (Loveys et al.
2000). PRD irrigation also improves water use efficiency by applying approximately half
the amount of irrigation water to the vines compared to standard drip irrigation practices.
This study aims to:
1. Evaluate the effects of irrigation and pruning treatments on canopy development.
2. Assess the influence of integrated irrigation and pruning treatments on berry
development and maturation.
3. Determine the effects of integrated irrigation and pruning treatments on yield
components at harvest.
The following hypothesis was tested:
The combination of light pruning levels of minimal pruning with PRD irrigation will
improve the “source-sink” carbohydrate relationship. Retaining greater number of nodes at
pruning will increase yield, whilst inducing a water-stress response in the grapevine by PRD
will control vegetative vigour.
3.2 METHODOLOGY
3.2.1 Canopy development and morphology
Vine morphology, canopy size and pruning weights were assessed on vines from each
irrigation and pruning treatment. However, vegetative growth was investigated for pruning
treatment effects only, as measurements were conducted monthly from October to
December 2000 before irrigations were applied for the 2000-01 growing season.
Chapter 3: Irrigation and pruning effects on yield 29
Primary shoot measurements were done on four representative shoots of eight replicate
vines from each pruning treatment. Shoot growth rate, length, internode number and
internode length were assessed. The length of the tagged shoot was measured from the basal
bud to the shoot tip and shoot growth rate was calculated as centimetres of growth per day.
Internode length was determined between the leaf four and five from the basal leaf on each
tagged shoot from each of the pruning treatments. Leaf area development of vines was
estimated monthly through the growing season in 2000-01 on 12 replicate vines using an
indirect optical method. The central vine from each plot of each row was measured using the
LAI-2000 canopy analyser (LI-COR Inc., Lincoln, Nebraska, USA) according to Sommer et
al. (1995).
Canopy size (total leaf area.vine-1) was estimated on fully developed canopies of six
replicate vines per treatment when primary shoot growth had ceased in subsequent seasons
using the LAI-2000 canopy analyser. Total leaf area.vine-1 was calculated using the
relationship between direct and indirect measurements of leaf area index from Sommer and
Lang’s (1994) LAI-2000 validation study. Maximum leaf area.vine-1 was measured on 22
November in three consecutive growing seasons (2000-02) on all treatments just prior to
summer trimming. Destructive sampling was used to assess mean pruning weight.vine-1
and cane number.vine-1 and mean cane weight was calculated (pruning weight.vine-1 /cane
number.vine-1) on six replicate vines on all treatments at winter pruning, 2003.
3.2.2 Berry Development
Mean berry weight and total soluble solids (TSS) were monitored at weekly intervals from
veraison to harvest as an indication of berry maturation for the three consecutive seasons.
Three vines per treatment were randomly selected each week and five bunches were
sampled in a diagonal cross-section from the bottom north-east corner, over the top of the
vine to the south-west corner. All berries were removed from the five bunches and 100
berries were randomly selected and weighed (g). The 100-berry sub-sample was crushed by
hand using a mortar and pestle; grape juice was then drained through a 2 mm gauze sieve.
Grape juice samples were left to settle for 1 hour and 1 mL extracted to measure TSS
Chapter 3: Irrigation and pruning effects on yield 30
(°Brix) using a temperature compensating PR-101 digital refractometer (Atago Co. Ltd.,
Tokyo, Japan).
3.2.3 Harvest Components
In the first season (2000-01) all six treatments were picked on the same day (124 days after
flowering, DAF) but in subsequent seasons (2001-02 and 2002-03) treatments were picked
at a maturity level of 24.0 ± 1.0 °Brix. The two central vines (Vines 4 and 5) of each
pruning plot in the six experimental irrigation rows were tagged as harvest vines: 12
replicate vines represented each treatment. At harvest, 1 m transects were assigned to either
the west, central or east region of the vine. Transect ladders (1 m wide) were used and all
bunches within the 1 m zone were counted, picked and weighed. Yield was calculated as
kg.vine-1 and t.ha-1 and mean bunch weight was calculated (yield kg.m-1/bunch number.m-1).
Sub-samples of 10 bunches were collected from each of the harvest vines and all berries
were plucked from the rachis. One hundred berries were randomly selected and weighed;
mean berry weight was calculated (100 berry weight g/100). A further 250 g of berries was
sampled and stored at –20°C for analysis of anthocyanin and phenolic concentration.
Leaf area to fruit ratio (LA:F) was calculated as the ratio of total leaf area per vine (cm2),
measured using the LAI-canopy analyser (as described in section 3.2.1) to yield per vine (g).
Water use efficiency (WUE) was calculated as the amount of yield produced (t.ha-1) per
mega-litre of irrigation water applied for each irrigation treatment over the growing season.
3.2.4 Statistical Analysis
Harvest data was analysed by Analysis of Variance (ANOVA) using GenStat® 6th Edition
(Lawes Agricultural Trust, Rothamsted Experimental Station). All interactions were
balanced and analysed by general ANOVA. The treatment structure was Irrigation*Pruning
and the blocking structure was Row*Plot (Appendix B for GenStat output). Treatment
effects at each sample collection date were analysed using ANOVA on maturation data.
Chapter 3: Irrigation and pruning effects on yield 31
3.3 RESULTS
3.3.1 Canopy Development and Morphology
Shoot Development
Imposed pruning treatments influenced all aspects of shoot development; shoot length,
growth rate, node number.shoot-1 and internode length, as shoot growth measurements
occurred before irrigation was applied in season 2000-01.
Shoot length
Mean shoot length was greater for SPUR vines at the start of shoot growth measurements
compared to MECH or MIN vines (Figure 3.1a). By 61 days after budburst (DAB), SPUR
and MECH vines had significantly longer shoots than MIN vines. Shoot elongation had
ceased by 89 DAB; SPUR shoots were 23% longer than MECH shoots, which in turn were
54% longer than MIN shoots.
Shoot Growth Rate
Shoot growth rate between 27 and 61 DAB was less on shoots from MIN vines compared to
SPUR and MECH vines (Figure 3.1b). The shoot growth rate of SPUR vines was greater
than MECH and MIN vines at both 61 and 89 DAB. The rate of shoot growth rapidly
declined from 2.2 cm.day-1 to 1.6 cm.day-1 for SPUR vines between 61 and 89 DAB,
whereas the decrease in shoot growth rate was less obvious on MIN vines.
Node Number.Shoot-1
The node number.shoot-1 was significantly less for SPUR vines compared to MECH and
MIN vines at 27 DAB (Figure 3.1c). However, by 61 DAB SPUR had the highest node
number.shoot-1 compared to the other pruning treatments. This trend continued with SPUR
having the highest number, MECH having an intermediate number and MIN vines having
the lowest node number.shoot-1 by the end of shoot elongation (89 DAB)
Internode Length
MIN vines had significantly shorter internodes than MECH or SPUR vines on all
measurement days (Figure 3.1d). The difference in internode length between pruning
treatments was much greater at 89 DAB than at 27 or 61 DAB.
Chapter 3: Irrigation and pruning effects on yield 32
Days after budburst
20 30 40 50 60 70 80 90 100
Sho
ot le
ngth
cm
0
20
40
60
80
100
120
140
160
180
Days after budburst
20 30 40 50 60 70 80 90 100
Sho
ot g
row
th ra
te c
m d
ay-1
0.4
0.6
0.8
1.0
1.2
1.4
1.6
1.8
2.0
2.2
2.4
2.6
Days after budburst
20 30 40 50 60 70 80 90 100
Nod
es S
hoot
-1
4
6
8
10
12
14
16
18
20
22
Days after budburst
20 30 40 50 60 70 80 90 100
Inte
rnod
e le
ngth
cm
0
10
20
30
40
50
60
70
Spur Mech Min
a. b.
c. d.
***
***
***
***
***
***
*****
***
***
*** ***
Figure 3.1: Pruning treatment effects on shoot growth in season 2000-01; a. shoot length, b. shoot growth rate, c. node number.shoot-1 and d. internode length from budburst to 89 days after budburst (DAB). Significant differences were calculated by Fisher’s least significant difference (LSD) at each time point. LSD is represented by bars and levels of significance are denoted by ***P<0.001, **P<0.01, *P<0.05.
3.3.2 Leaf Area Development
Total Leaf Area development
Total leaf area development of vines during the 2000-01 growing season showed leaf
expansion from budburst to 22 November (42 DAB) was greater for MIN compared to
Chapter 3: Irrigation and pruning effects on yield 33
MECH and SPUR vines (Figure 3.2a). Between 42 DAB and 68 DAB, summer trimming of
all vines occurred and total leaf area.vine-1 of MIN vines was similar to both SPUR and
MECH vines. No significant pruning effects were found for the remainder of the growing
season. However, the rate of leaf area development was higher for SPUR vines later in the
growing season due to the increase in lateral shoot growth. Irrigation influenced leaf area
development towards the end of the growing season (Figure 3.2b). SD increased the rate of
leaf area development between 18 December (68 DAB) and 13 February (124 DAB)
compared to PRD irrigation. Total leaf area.vine-1 of SD irrigated vines was 17% larger
than PRD irrigated vines prior to harvest.
Days after budburst
0 20 40 60 80 100 120 140
Tota
l Lea
f Are
a m
2 vin
e-1
5
10
15
20
25
30
35
SD PRD
Days after budburst
0 20 40 60 80 100 120 140
Tota
l lea
f are
a m
2 vin
e-1
5
35
30
25
20
15
10
Spur Mech Min
***
***
* ns
*
ns
***
ns
ns
ns
a. b.
Figure 3.2: a Pruning and b. Irrigation effects on total leaf area development n season 2000-01. Significant differences were calculated by Fisher’s least significant difference (LSD) at each time point. Levels of significance are denoted by ***P<0.001, **P<0.01, *P<0.05, ns = not significant.
Maximum leaf area.vine-1
The integration of pruning and irrigation or irrigation alone had no significant effect on
maximum leaf area.vine-1 over the three seasons. However, differences in maximum leaf
area.vine-1 between the three pruning treatments were observed; MIN produced a higher
total leaf area.vine-1 than SPUR (22%) or MECH (16%) (Table 3.1).
Chapter 3: Irrigation and pruning effects on yield 34
Table 3.1: Irrigation and pruning effect on total leaf area.vine-1 (LA m2.vine-1) at maximum canopy development, 22 November 2000-02. * Indicates significance level; *** P<0.001, ** P<0.01, * P<0.05, ns = non significant.
Irrigation LA m2.vine-1 Pruning LA m2.vine-1
SD 23.1 SPUR 20.7a PRD 22.1 MECH 21.9a MIN 25.3b Irrigation P value ns Pruning P value ***
3.3.3 Pruning Weights
The application of PRD irrigation alone or the integration between irrigation and pruning
treatments did not affect pruning weights, cane number and mean cane weight (Table 3.2).
However, there was a pruning response for all parameters. SPUR had a higher mean pruning
weight than MECH and MIN by 2.5-fold and 3.2-fold respectively. MIN increased cane
number.vine-1 compared to MECH and SPUR by 1.8-fold and 2.2-fold respectively. Mean
cane weight was greater for SPUR relative to MECH and MIN by 1.5-fold and 6.5-fold.
Hence, severe pruning to 60 nodes produced more one-year old wood and enhanced shoot
vigour more than lighter pruning treatments.
Table 3.2: Irrigation and pruning effects on pruning weight, cane number.vine-1 and mean cane weight at winter pruning in season 2002-03. * Indicates significance level; *** P<0.001, ** P<0.01, * P<0.05, ns = not significant, different letters denote significant differences between means in each column.
Treatment Pruning Wt. (kg) Cane Number.Vine-1 Cane Wt. (g) Grand Mean 1.3 111.9 14.9 SD 1.4 114.3 15.4 PRD 1.3 109.6 14.4 Irrigation ns ns ns SPUR 1.9c 77.0a 24.8c MECH 1.5b 93.2b 16.1b MIN 0.6a 165.6c 3.8a Pruning *** *** *** SD + SPUR 2.0 78.0 25.6 PRD + SPUR 1.8 76.0 24.0 SD + MECH 1.6 94.5 16.9 PRD + MECH 1.4 91.8 15.3 SD + MIN 0.6 170.3 3.6 PRD + MIN 0.6 160.8 4.0 Irrigation*Pruning ns ns ns
Chapter 3: Irrigation and pruning effects on yield 35
3.3.4 Berry Development
Berry Weight
Two stages of berry weight change were observed each season between veraison and
harvest. The first period (Period 1) involved a gradual increase in berry weight between
veraison and 20 to 34 days after veraison, depending on the imposed treatment. In the
second period (Period 2) there was a slow decline in berry weight from 34 days after
veraison to harvest because of berry shrivel. The mean rate of berry weight increase across
all treatments in Period 1 was consistent over the 3 seasons (0.011 g.day-1). However, the
rate of berry weight loss in Period 2 was season-dependent, ranging from -0.007 g.day-1 in
season 2002-03 to -0.010 g.day-1 in season 2001-02.
The treatment trends for berry weight accumulation were comparable for all three
experimental seasons (Figure 3.3, 3.4, 3.5). However, the final berry weight differences
between treatments were greater in seasons 2001-02 and 2002-03 than 2000-01, when
treatments had been imposed for more than 2 or more seasons. Initial berry weight at the
onset of veraison was influenced by the imposed irrigation and pruning treatments. Initial
berry weight and berry weight throughout the maturation period was greatest for SD +
SPUR for all 3 seasons. Variation was also large for SD + SPUR compared to treatments
that produced smaller berries. SD + MECH, PRD + SPUR, SD + MIN and PRD + MIN had
progressively smaller initial berry weights and this trend continued through the maturation
period. The lowest berry weight throughout the maturation period for each season was
produced by PRD + MIN.
3.3.5 Berry Maturation
Sugar Accumulation
TSS was measured weekly to give an indication of sugar accumulation in the berries. Initial
sugar concentration varied across treatments in the three experimental seasons. This
suggests delayed veraison, particularly for lightly pruned treatments with high bunch
numbers per vine (MIN and MECH).
Chapter 3: Irrigation and pruning effects on yield 36
Days after veraison
10 20 30 40 50
Mea
n Be
rry W
eigh
t (g)
0.6
0.8
1.0
1.2
1.4
1.6
1.8
2.0
SD+Spur PRD+Spur SD+Mech PRD+Mech SD+Min PRD+Min
***
***
*
**
*****
***
**
Figure 3.3: Irrigation and pruning effects on berry weight during the maturation period in season 2000-01. Significance of irrigation and pruning interactions were calculated by Fisher’s LSD and are represented on the graph by LSD bars. Levels of significance are denoted by *** P<0.001, ** P<0.01, * P<0.05, ns = not significant.
Days after veraison
10 20 30 40 50
Mea
n B
erry
Wei
ght (
g)
0.6
0.8
1.0
1.2
1.4
1.6
1.8
2.0
2.2SD+Spur PRD+Spur SD+Mech PRD+Mech SD+Min PRD+Min
** *
**
***
ns
***
Figure 3.4: Irrigation and pruning effects on berry weight during the maturation period in season 2001-02. Significance of irrigation and pruning interactions were calculated by Fisher’s LSD and are represented on the
Chapter 3: Irrigation and pruning effects on yield 37
graph by LSD bars. Levels of significance are denoted by *** P<0.001, ** P<0.01, * P<0.05, ns = not significant.
Days after veraison
10 20 30 40
Mea
n Be
rry W
eigh
t (g)
0.6
0.8
1.0
1.2
1.4
1.6
1.8
2.0
SD+Spur PRD+Spur SD+Mech PRD+Mech SD+Min PRD+Min
ns
ns ** ** ***
***
**
***
Figure 3.5: Irrigation and pruning effects on berry weight during the maturation period in season 2002-03. Significance of irrigation and pruning interactions were calculated by Fisher’s LSD and are represented on the graph by LSD bars. Levels of significance are denoted by *** P<0.001, ** P<0.01, * P<0.05, ns = not significant.
Sugar Accumulation, season 2000-01
In season 2000-01, the pruning treatments had an overriding influence on sugar
accumulation, as a response to crop load (Figure 3.6). SPUR treatments reached maturity
first, followed by MECH and MIN treatments. SPUR pruning had a lower crop load than
MECH or MIN pruning in 2001. Thus the number of potential sink sites (bunches) for
carbohydrates produced by SPUR pruned vines was lower than higher yielding treatments.
Sugar Accumulation, season 2001-02
PRD irrigation influenced sugar accumulation in season 2001-02 (Figure 3.7). Berries from
vines irrigated by PRD had a greater initial sugar concentration than SD irrigated vines for
all pruning treatments. PRD + SPUR and PRD + MECH reached 24 °Brix 13 days earlier
than other treatments. SD + MIN had the lowest TSS levels throughout the ripening period
between veraison and harvest.
Chapter 3: Irrigation and pruning effects on yield 38
Figure 3.6: Irrigation and pruning effects on sugar (TSS) accumulation during the maturation period in season 2000-01. Significance of irrigation and pruning interactions were calculated by Fisher’s LSD and are represented on the graph by LSD bars. Levels of significance are denoted by *** P<0.001, ** P<0.01, * P<0.05, ns = not significant.
Days after veraison
10 20 30 40 50
Tota
l Sol
uble
Sol
ids
(o Brix
)
12
14
16
18
20
22
24
26
SD+Spur PRD+Spur SD+Mech PRD+Mech SD+Min PRD+Min
*
***
*
ns*
**
** **
Days after veraison
10 20 30 40 50
Tota
l Sol
uble
Sol
ids
(o Brix
)
12
14
16
18
20
22
24
26
28
SD+Spur PRD+Spur SD+Mech PRD+Mech SD+Min PRD+Min
ns
**
***
** * ns*
Figure 3.7: Irrigation and pruning effects on sugar (TSS) accumulation during the maturation period in season 2001-02. Significance of irrigation and pruning interactions were calculated by Fisher’s LSD and are represented on the graph by LSD bars. Levels of significance are denoted by *** P<0.001, ** P<0.01, * P<0.05, ns = not significant.
Chapter 3: Irrigation and pruning effects on yield 39
Sugar Accumulation, season 2002-03
The treatment differences in sugar accumulation were less apparent in 2002-03 (Figure 3.8).
PRD + MECH and SD + MIN reached 24 °Brix 10 days earlier than the other treatments.
This was the result of a rapid increase in sugar concentration in berries after a major rainfall
event 34 days after veraison.
Days after veraison
10 20 30 40
Tota
l Sol
uble
Sol
ids
(o Brix
)
14
16
18
20
22
24
26
SD+Spur PRD+Spur SD+Mech PRD+Mech SD+Min PRD+Min
ns
*
ns
ns ns
ns nsns
Figure 3.8: Irrigation and pruning effects on sugar (TSS) accumulation during the maturation period in season 2002-03. Significance of irrigation and pruning interactions were calculated by Fisher’s LSD and are represented on the graph by LSD bars. Levels of significance are denoted by *** P<0.001, ** P<0.01, * P<0.05, ns = not significant.
Sugar Accumulation Regression Models
Three linear regression models were fitted to the rate of TSS increase for each season to test
which model provided best representation of the treatment effects. The three linear
regression models tested were distinct regression lines for each treatment, parallel regression
lines for each treatment and a common regression line of all treatments. Equations of the
regression models and coefficients of determination (R2) for each regression line are
presented in Table 3.3. The rates of sugar accumulation for season 2000-01 and 2001-02
were best fitted to parallel regression lines for each of the six treatments (Figure 3.9 and
Chapter 3: Irrigation and pruning effects on yield 40
3.10, R2 values presented in Table 3.3). Therefore, the rates of sugar accumulation in berries
from all six treatments were consistent for each season but the start of sugar accumulation
(veraison) varied between treatments. The rate of sugar accumulation was greater in season
2001-02 than the previous season, since regression line slopes were 0.245 and 0.196
respectively. Sugar accumulation in season 2002-03 was best fitted to a common regression
line (R2 = 0.89), which suggests the rate of maturation and the start of veraison was similar
for all six treatments (Figure 3.11).
Table 3.3: Equations and coefficient of determination (R2) for parallel regression model of sugar accumulation for seasons 2000-01 and 2001-02 and common regression model of sugar accumulation for season 2002-03. Regression model Equations are Total Soluble Solids = constant + slope*Days After Veraison.
Treatment Rate of Sugar Accumulation 2001 Parallel Regression Constant Slope R2
SD + SPUR 14.30 0.196 0.96 PRD + SPUR 13.45 0.196 0.95 SD + MECH 12.91 0.196 0.95 PRD + MECH 14.17 0.196 0.95 SD + MIN 13.57 0.196 0.93 PRD + MIN 12.21 0.196 0.93 2002 Parallel Regression Constant Slope R2
SD + SPUR 12.85 0.246 0.93 PRD + SPUR 15.21 0.246 0.94 SD + MECH 12.55 0.246 0.87 PRD + MECH 14.20 0.246 0.98 SD + MIN 10.81 0.246 0.92 PRD + MIN 12.12 0.246 0.96 2003 Common Regression Constant Slope R2
All treatments (6) 15.412 0.218 0.89 Figure 3.9: Parallel regression model of sugar accumulation in berries on vines with integrated irrigation and pruning treatments for season 2000-01. Refer to Table 3.3 for equations.
12.00
14.00
16.00
18.00
20.00
22.00
24.00
74 79 84 89 94 99 104 109 114 119DAF
Tota
l Sol
uble
Sol
ids
(o Brix
)
SD+SpurPRD+SpurSD+MechPRD+MechSD+MinPRD+Min
Chapter 3: Irrigation and pruning effects on yield 41
Figure 3.10: Parallel regression model of sugar accumulation in berries from vines with integrated irrigation and pruning treatments for season 2001-02. Refer to Table 3.3 for equations.
12.00
14.00
16.00
18.00
20.00
22.00
24.00
26.00
76 81 86 91 96 101 106 111 116
DAF
Tota
l Sol
uble
Sol
ids
(o Brix
)
SD+SpurPRD+SpurSD+MechPRD+MechSD+MinPRD+Min
12.0
14.0
16.0
18.0
20.0
22.0
24.0
26.0
76 81 86 91 96 101 106 111 116
DAF
Tota
l Sol
uble
Sol
ids
(o Brix
)
SD+SpurPRD+SpurSD+MechPRD+MechSD+MinPRD+Min
Figure 3.11: Common regression model of sugar accumulation in berries from vines with integrated irrigation and pruning treatments for season 2002-03. Refer to Table 3.3 for equations.
Sugar Accumulation Rate
The rate of sugar accumulation (°Brix.day-1) varied between seasons (Table 3.4). The rate
was greater in seasons 2001-02 and 2002-03 compared to 2000-01. No difference in the rate
of sugar accumulation was observed between treatments in each season but PRD + SPUR
Chapter 3: Irrigation and pruning effects on yield 42
and PRD + MECH had a more rapid rate of sugar accumulation compared to other
treatments in season 2001-02.
Table 3.4: Integrated treatment effects on sugar accumulation rate (°Brix.day-1) for seasons 2000-01, 2001-02 and 2002-03. Different letters denote significant differences between seasonal means. *** indicates P<0.001.
Treatment Rate of Sugar Accumulation (°Brix.day-1) 2001 2002 2003 SD + SPUR 0.20 0.25 0.23 PRD + SPUR 0.20 0.29 0.24 SD + MECH 0.21 0.24 0.22 PRD + MECH 0.19 0.29 0.25 SD + MIN 0.18 0.24 0.27 PRD + MIN 0.21 0.23 0.25 Season Mean *** 0.20a 0.26b 0.24b
3.3.6 Bunch Number and Bunch Weight
Bunch Number.Vine-1
The level of pruning had a significant effect on bunch number.vine-1 but irrigation
treatments had no effect for the three experimental seasons (Table 3.5). Since irrigation did
not influence bunch number.vine-1, there were no significant interactions between irrigation
and pruning treatments. Seasonal variation had a large influence on bunch number.vine-1.
Bunch number.vine-1 for the two irrigation treatments and light pruning treatments (MECH
and MIN) were heavily reduced in season 2002-03 compared to the two previous seasons
due to poor bunch initiation.
The pruning effect on bunch number.vine-1 was large in seasons 2000-01 and 2001-02. A
2.0-fold increase in bunch number.vine-1 from SPUR to MECH and 4.2-fold from SPUR to
MIN was recorded for season 2000-01. Bunch number.vine-1 increased 2.5-fold from SPUR
vines to MECH vines and 4.6-fold from SPUR to MIN vines in season 2001-02. However,
the difference in bunch number.vine-1 between pruning treatments was significantly less in
2002-03. A 1.3-fold increased in bunch number.vine-1 was recorded from SPUR to MECH
and a 2.3-fold increase from SPUR to MIN. Light pruning treatments, MIN and MECH
were greatly affected by seasonal variation. Large reductions in bunch number.vine-1 were
found for both MIN and MECH in season 2002-03 compared to the previous seasons.
Chapter 3: Irrigation and pruning effects on yield 43
However, no year-to-year variation was recorded for SPUR because of the increased crop
control associated with severe pruning.
TABLE 3.5: Bunch number.vine-1 of vines with integrated irrigation and pruning treatments and seasonal means for 2000-01, 2001-02, 2002-03. Different letters denote significant differences between treatment means for each season (column) and across seasons (rows), as calculated by Fisher’s least significant difference (LSD 5% level). Significant differences between treatments are denoted by *** P<0.001, ** P<0.01, * P<0.05, ns= not significant.
Bunch Number.Vine-1
Treatment 2000-01 2001-02 2002-03 Grand Mean Season LSD
Seasonal Mean 330 379 159 290 *** 22.2 SD 349 348 150 280 PRD 312 370 169 283 Irrigation ns ns ns ns ** 63.9 SPUR 137a 140a 102a 126a MECH 275b 345b 137b 252b MIN 580c 641c 239c 478c Pruning *** *** *** *** *** 52.1 SD + SPUR 128 147 96 124 PRD + SPUR 144 132 108 127 SD + MECH 280 368 141 263 PRD + MECH 269 322 132 241 SD + MIN 637 618 212 473 PRD + MIN 523 657 267 482 Irrigation*Pruning ns ns ns ns ** 82.4
Mean Bunch Weight
Mean Bunch weight was also strongly affected by imposed pruning treatments and seasonal
variation (Table 3.6). The influence of pruning treatments on bunch weight was consistent
for the three experimental seasons; SPUR bunches > MECH bunches > MIN bunches.
Bunch weight was reduced by MECH by 35% compared to SPUR and a further 42%
reduction was recorded from MECH to MIN. Irrigation treatments only affected bunch
weight in season 2002-03 with PRD reducing bunch weight by 28% compared to SD
irrigation. As a consequence of the limited influence irrigation treatments imposed on mean
bunch weight, no significant interactions between irrigation and pruning were found for the
three experimental seasons.
A significant negative linear relationship was found between bunch number.vine-1 and mean
bunch weight across all treatments in each season. The greater the bunch number.vine-1, the
smaller the resultant bunch weights. The coefficient of determination and level of
significance for each season are presented in Table 3.7.
Chapter 3: Irrigation and pruning effects on yield 44
TABLE 3.6: Bunch weight (g) of vines with integrated irrigation and pruning treatments and seasonal means for 2000-01, 2001-02, 2002-03. Different letters denote significant differences between treatment means for each season (column) and across seasons (rows), as calculated by Fisher’s least significant difference (LSD 5% level). Significant differences between treatments are denoted by *** P<0.001, ** P<0.01, * P<0.05, ns= not significant.
Bunch Weight g
Treatment 2000-01 2001-02 2002-03 Grand Mean Season LSD
Season Mean 59.8 58.9 71.2 63.3 *** 4.1 SD 64.0 69.8 82.6b 72.2b PRD 55.7 52.2 59.7a 55.8a Irrigation ns ns ** * ** 12.9 SPUR 88.0c 100.3c 94.2c 94.1c MECH 59.1b 48.9b 74.4b 60.8b MIN 32.6a 26.6a 44.9a 35.1a Pruning *** *** *** *** *** 9.2 SD + SPUR 96.0 111.6 112.2 106.6 PRD + SPUR 80.1 89.0 76.2 81.6 SD + MECH 61.5 55.7 83.9 67.0 PRD + MECH 56.7 42.1 64.8 54.5 SD + MIN 34.7 28.3 51.7 39.5 PRD + MIN 30.4 25.4 38.1 31.3 Irrigation*Pruning ns ns ns ns ns 15.6
Table 3.7: Coefficient of determination (R2) and statistical significance level (P value) of the negative linear relationship between bunch number.vine-1 and bunch weight for all treatments in each season and over the 3 seasons. Significance level is denoted by ** P<0.01, * P<0.05.
Season R2 P value
2000-01 0.86 **
2001-02 0.82 **
2002-03 0.75 *
Mean 0.83 *
3.3.7 Yield
Yield was influenced by seasonal variation. A large decrease in yield was found in
association with the decrease in bunch number.vine-1 in season 2002-03 relative to the
preceding seasons. Irrigation influenced yield in seasons 2001-02 and 2002-03 and pruning
practices influenced yield in seasons 2000-01 and 2001-02 (Table 3.8). Combined irrigation
and pruning treatments did not have a significant effect on yield in any experimental season.
PRD irrigation reduced yield relative to SD irrigation in seasons 2001-02 and 2002-03 by
23% and 18% respectively. The lower yield in response to PRD corresponded to reductions
in berry weight (Refer to section 3.5.4). Pruning levels strongly influenced yield in the first
Chapter 3: Irrigation and pruning effects on yield 45
two experimental seasons, when bunch numbers were very different between treatments.
Yield was higher on lightly pruned treatments compared to SPUR pruning. The high yield
produced by MIN vines in season 2000-01 may be attributed to the retention of a high
number of nodes at winter pruning. Pruning level did not influence yield in season 2002-03,
when bunch numbers were relatively consistent between treatments.
There was no significant interactive effect of irrigation and pruning treatments on yield
because of the additive effects of SD irrigation and light pruning treatments. However,
interesting trends were observed in each season. PRD reduced yield by 28% when
combined with MIN in season 2000-01, whereas reductions in the following two seasons
were only 7% and 5%. However, the seasonal trend in yield reductions by PRD was
reversed for both SPUR and MECH vines. A small decrease by PRD was observed in
season 2000-01 for SPUR and MECH vines and large decreases were observed in the
subsequent seasons.
TABLE 3.8: Yield of vines with integrated irrigation and pruning treatments and seasonal means for 2000-01, 2001-02, 2002-03. Different letters denote significant differences between treatment means for each season (column) and across seasons (rows), as calculated by Fisher’s least significant difference (LSD 5% level). Significant differences between treatments are denoted by *** P<0.001, ** P<0.01, * P<0.05, ns= not significant.
Yield kg.vine-1
Treatment 2000-01 2001-02 2002-03 Grand Mean Season LSD
Season mean 15.6 16.1 10.1 14.0 *** 1.13 SD 17.1 17.9b 11.1b 15.2b PRD 14.2 13.8a 9.1a 12.4a Irrigation ns * * * * 3.08 SPUR 11.7a 13.9a 9.5 11.7a MECH 16.1b 16.7b 10.1 14.3b MIN 19.2c 16.7b 10.7 15.4b Pruning *** ** ns *** *** 2.40 SD + SPUR 12.2 16.1 10.7 13.0 PRD + SPUR 11.3 11.6 8.4 10.4 SD + MECH 16.9 19.9 11.6 16.1 PRD + MECH 15.3 13.6 8.6 12.5 SD + MIN 22.3 17.4 10.9 16.8 PRD + MIN 16.1 16.1 10.4 14.2 Irrigation*Pruning ns ns ns ns * 3.91
Chapter 3: Irrigation and pruning effects on yield 46
3.3.8 Berry Weight and Berry Number
Berry Weight
Both PRD irrigation and MIN pruning significantly reduced mean berry weight in each
season (Table 3.9). An interaction effect was found between irrigation and pruning
treatments for mean berry weight in season 2001-02. Also, seasonal variation influenced
berry weight; the largest berries developed in the first experimental season (2000-01) and
the smallest berries developed in the following season (2001-02).
Irrigation had a significant effect on berry weight for each season; PRD reduced berry
weight by 19% compared to SD. Pruning also had a significant effect on berry weight in all
seasons. SPUR produced the largest berries and MIN produced the smallest, possibly as a
response to bunch number.vine-1. No difference in berry weight was found for SPUR
between the three seasons. However, berry weight from MECH and MIN treatments were
influenced by seasonal variation.
There was a significant interaction between irrigation and pruning treatments for mean berry
weight in 2001-02. A large decrease (42%) was observed from the treatment with the
largest berries (SD + SPUR) to that with the smallest berries (PRD + MIN). PRD irrigation
resulted in reductions in berry weight when vines were SPUR (24%) or MECH (20%)
pruned. However, berry weight of MIN vines was not significantly reduced by PRD. There
was also a significant interaction for berry weight between irrigation and pruning treatments
in the three seasons. Berry size was reduced by PRD compared to SD when combined with
all pruning treatments but the magnitude of reduction by PRD was greater on SPUR and
MECH vines than MIN vines.
Berry Number.Bunch-1
Mean berry number.bunch-1 progressively increased over the experimental period, which
relates to flower number and fruit-set (Table 3.10). Pruning level had a significant effect on
berry number.bunch-1. However, neither irrigation nor the combination of irrigation and
pruning had any effect on berry number.bunch-1.
Chapter 3: Irrigation and pruning effects on yield 47
Berry number.bunch-1 was reduced from SPUR to MECH (31%) and from MECH to MIN
(30%) in the three seasons. The number of berries per bunch increased in 2002-03 for
MECH and MIN but decreased for SPUR compared to the previous two seasons. Therefore
a change in bunch architecture occurred in 2002-03 for MECH and MIN, i.e. more compact
bunches with more berries per bunch (Refer to section 6.3.5).
TABLE 3.9: Berry weight of vines with integrated irrigation and pruning treatments and seasonal means for 2000-01, 2001-02, 2002-03. Different letters denote significant differences between treatment means for each season (column) and across seasons (rows), as calculated by Fisher’s least significant difference (LSD 5% level). Significant differences between treatments are denoted by *** P<0.001, ** P<0.01, * P<0.05, ns= not significant.
Berry Weight (g)
Treatment 2000-01 2001-02 2002-03 Grand Mean Season LSD
Season Mean 1.21 1.01 1.14 1.12 *** 0.03 SD 1.32b 1.14b 1.26b 1.24b PRD 1.11a 0.91a 1.03a 1.01a Irrigation * ** ** ** ns 0.14 SPUR 1.30c 1.19c 1.25b 1.25b MECH 1.22b 1.01b 1.23b 1.15b MIN 1.12a 0.81a 0.95a 0.97a Pruning *** *** *** *** *** 0.06 SD + SPUR 1.43 1.35e 1.41 1.40c PRD + SPUR 1.17 1.02c 1.09 1.09b SD + MECH 1.33 1.12d 1.30 1.25c PRD + MECH 1.10 0.90b 1.15 1.05b SD + MIN 1.19 0.84a 1.05 1.05b PRD + MIN 1.05 0.79a 0.84 0.89a Irrigation*Pruning ns ** ns ** * 0.15
TABLE 3.10: Berry number.bunch-1 of vines with integrated irrigation and pruning treatments and seasonal means for 2000-01, 2001-02, 2002-03. Different letters denote significant differences between treatment means for each season (column) and across seasons (rows), as calculated by Fisher’s least significant difference (LSD 5% level). Significant differences between treatments are denoted by *** P<0.001, ** P<0.01, * P<0.05, ns= not significant.
Berry Number.Bunch-1
Treatment 2000-01 2001-02 2002-03 Grand Mean Season LSD
Season Mean 48.8 55.2 60.6 54.9 *** 3.2 SD 48.0 58.0 64.3 56.6 PRD 49.9 55.2 57.2 54.0 Irrigation ns ns ns ns * 6.7 SPUR 68.3c 84.5c 75.0c 75.8c MECH 49.3b 48.1b 60.1b 52.5b MIN 29.1a 32.9a 46.8a 36.5a Pruning *** *** *** *** *** 6.9 SD + SPUR 67.8 82.5 79.3 76.6 PRD + SPUR 68.9 86.6 70.7 75.1 SD + MECH 46.9 49.6 63.8 53.4 PRD + MECH 51.7 46.6 56.3 51.6 SD + MIN 29.3 33.9 49.0 37.8 PRD + MIN 29.0 32.2 44.7 35.3 Irrigation*Pruning ns ns ns ns ns 10.1
Chapter 3: Irrigation and pruning effects on yield 48
3.3.9 Vine Balance
Leaf Area: Fruit Ratio
The ratio of total leaf area.vine-1 and yield (LA:F) was used as an indication of vine balance
between vegetative and reproductive growth. No significant interaction or irrigation effects
were found. However, in general, LA:F was greater for PRD, as a response to lower yield.
A significant pruning effect was observed in 2000-01: MECH and MIN reduced the LA:F
ratio compared to SPUR (30% and 25% respectively) (Table 3.11). Therefore, less leaf area
was required to mature 1 g of fruit mass on MECH and MIN vines than on SPUR vines.
TABLE 3.11: Leaf area: fruit ratio of vines with integrated irrigation and pruning treatments and seasonal means for 2000-01, 2001-02, 2002-03. Different letters denote significant differences between treatment means for each season (column) and across seasons (rows), as calculated by Fisher’s least significant difference (LSD 5% level). Significant differences between treatments are denoted by *** P<0.001, ** P<0.01, * P<0.05, ns= not significant.
Leaf Area (cm2): Fruit (g) Ratio
Treatment 2000-01 2001-02 2002-03 Grand Mean Season LSD
Season Mean 18.8 16.4 19.2 18.1 ** 1.87 SD 17.9 14.8 16.8 16.3 PRD 19.2 18.3 22.3 19.9 Irrigation ns ns ns ns * 4.30 SPUR 21.6b 17.5 20.8 20.0b MECH 16.5a 15.0 17.4 16.3a MIN 17.6a 17.5 19.2 18.1ab Pruning * ns ns * ns 4.10 SD + SPUR 23.0 15.8 15.8 18.2 PRD + SPUR 20.1 19.3 25.9 21.9 SD + MECH 15.7 12.9 14.7 14.4 PRD + MECH 17.2 17.1 20.1 18.1 SD + MIN 15.0 16.1 17.5 16.2 PRD + MIN 20.2 18.3 21.0 19.8 Irrigation*Pruning ns ns ns ns ns 6.11
Water Use Efficiency
WUE (t.ML-1) was greater for each treatment in 2001-02 than in any other season because of
the higher yields recorded during this season. WUE was improved by PRD relative to SD by
1.4, 1.6, 1.3-fold in seasons 2000-01, 2001-02 and 2002-03, respectively. MIN and MECH
significantly improved WUE compared to SPUR in 2000-01 and 2001-02 but no pruning
effect was found in 2002-03 due to reduced yield. No significant interactions were observed
between irrigation and pruning treatments (Table 3.12). However, a 2-fold improvement in
Chapter 3: Irrigation and pruning effects on yield 49
WUE by PRD + MIN compared to SD + SPUR was recorded in 2000-01 and 2001-02, as a
response to lower irrigation inputs and higher yield.
TABLE 3.12: Water use efficiency of vines with integrated irrigation and pruning treatments and seasonal means for 2000-01, 2001-02, 2002-03. Different letters denote significant differences between treatment means for each season (column) and across seasons (rows), as calculated by Fisher’s least significant difference (LSD 5% level). Significant differences between treatments are denoted by *** P<0.001, ** P<0.01, * P<0.05, ns= not significant.
Water Use Efficiency (t.ML-1)
Treatment 2000-01 2001-02 2002-03 Grand Mean Season LSD
Season Mean 5.32 6.36 3.66 5.11 *** 0.44 SD 4.4a 4.9a 3.0a 4.0a PRD 6.3b 7.7b 4.3b 6.1b Irrigation * ** *** ** * 0.91 SPUR 4.1a 5.4a 3.3 4.3a MECH 5.5b 6.5b 3.4 5.2b MIN 6.4c 7.3b 3.6 5.8b Pruning *** ** ns *** * 0.91 SD + SPUR 3.1 4.4 2.8 3.5 PRD + SPUR 5.0 6.5 4.0 5.1 SD + MECH 4.3 5.5 3.1 4.3 PRD + MECH 6.8 7.5 4.1 6.1 SD + MIN 5.7 4.8 2.9 4.4 PRD + MIN 7.2 9.0 4.9 7.0 Irrigation*Pruning ns ns ns ns ns 1.34
3.4 DISCUSSION
3.4.1 Pruning and irrigation effects on canopy development
The level of pruning influenced canopy development, morphology, shoot growth, maximum
leaf area and consequently, the balance between reproductive and vegetative growth. MIN
changed the morphology of the Shiraz grapevine framework to produce large permanent
woody structures. In terms of total leaf area, pruning treatments had a significant effect on
canopy development from budburst to fruit-set, as a direct result of higher bud numbers
retained after winter pruning. MIN and MECH vines developed full canopies earlier in the
growing season than SPUR vines, as previously reported by Downton and Grant (1992) and
Sommer et al. (1993). Therefore net photosynthesis and subsequently, cumulative carbon
production may have been greater for MIN and MECH vines, having a beneficial effect on
growth and fruit development. Shoot growth and subsequently, canopy morphology was
altered by light pruning levels. MIN and MECH produced large numbers of smaller shoots
with shorter internode lengths and reduced node number, as a result of increased vegetative
Chapter 3: Irrigation and pruning effects on yield 50
sink competition and partitioning of carbohydrates. These results agree with reports by
Clingeleffer (1984) and McCarthy and Cirami (1990). Vegetative “vigour”, as determined
by pruning weights at the end of the growing seasons was increased by severe pruning
treatments compared to light pruning treatment because of rapid growth of 1-year old wood
on SPUR vines. As a consequence of shoot growth dominance of SPUR vines, the balance
between vegetative and reproductive growth was altered compared to lightly pruned
treatments. Summer pruning was imposed in December to achieve vine balance and allow
machinery access to the vineyard.
Canopy development was largely unaffected by irrigation treatments, since the majority of
vegetative growth occurred before irrigation was applied each season. However, total leaf
area of the vine was reduced by the application of PRD between late November and March.
The reduced total leaf area of PRD vines was consistent with reduced canopy biomass
reported for Cabernet Sauvignon in response to PRD (Loveys et al. 1998). The reduction in
canopy biomass caused by PRD may have been associated with reduced leaf size or
restricted development of lateral shoots, as a result of ABA synthesis in the dry rootzones.
A reduction in total leaf area after veraison may have negative repercussions on fruit
development and maturation, if net photosynthesis and subsequently carbon production is
sufficiently reduced. Alternatively, increased bunch exposure due to fewer leaves per vine
or smaller leaves may enhance fruit quality, in particular anthocyanin and phenolic
concentrations.
Surprisingly, PRD irrigation had no influence on pruning weight in this study, given results
from previous work (Dry and Loveys 1998; Loveys et al. 1998) and its effect on total leaf
area. PRD field and split-pot experiments conducted on Shiraz, Cabernet Sauvignon and
Riesling have demonstrated a reduction in pruning weight, as well as shoot growth rate and
leaf area in relation to the biochemical responses produced by PRD (Dry et al. 1996; Dry
and Loveys 1998, 1999). Since total leaf area was reduced but pruning weight was
unaffected in this study, this suggests that PRD had a greater affect on canopy biomass and
lateral growth than on primary shoot growth. The lack of influence of PRD on pruning
weight may be a consequence of the integration with pruning systems, particularly in the
first experimental season when pruning treatments had an overriding effect on canopy
development.
Chapter 3: Irrigation and pruning effects on yield 51
3.4.2 Treatment effects on berry development
Pruning and irrigation effects on berry weight were apparent at the onset of veraison in all
three seasons; MIN and PRD reduced berry weight prior to veraison compared to other
treatment combinations. Partitioning of carbon between more sinks per vine combined with
a PRD-induced hormonal (ABA) response during the initial phase of berry development
between flowering and veraison, may have caused the low initial berry weight of PRD +
MIN vines. It is well established that berry size is most influenced by stress factors between
flowering and veraison, which coincides with the phase of pericarp cell division (Hardie and
Considine 1976; Matthews et al. 1987; McCarthy 1997). It has previously been accepted
that early water deficits reduce the rate of cell division of the pericarp, which only occurs
during the initial stages of berry growth. However, Ojeda et al. (2001) used DNA extraction
profiles to show water deficits do not affect cell division of Syrah berries but rather cause a
reduction in pericarp volume. This suggests that water deficits or water deficit responses
induced by PRD may modify the structural properties of the cell components, such as
flexibility, thereby limiting cell enlargement.
The rate of berry weight increase between veraison and harvest occurred in two stages and
was constant between all pruning and irrigation treatments. Period 1 involved an initial rapid
increase in berry weight with cell expansion and water accumulation in the berry. This was
followed by a slow decline of berry weight (Period 2) due to differential water loss, a
phenomenon commonly associated with Shiraz (McCarthy 1999). These results suggest a
pre-veraison restriction in cell division and solvent accumulation (predominantly water) in
berries but cell expansion and solute accumulation (predominantly diffusible sugars) after
veraison was not affected by pruning or irrigation treatments. The restrictions on berry
expansion by MIN and PRD before veraison may be explained by increased carbohydrate
partitioning between greater numbers of sinks and decreased cell wall flexibility
respectively. The constancy in the rate of sugar accumulation after veraison is well
documented for various growing conditions and berry sizes (Coombe 1980, 1984; Coombe
and Phillips 1982; Coombe et al. 1987). Brown and Coombe (1984) have suggested that
sugar accumulation in grape berries is an increase in diffusible sugars and suggested the
primary control was unloading from the phloem into the apoplast. However, if phloem sap
in the berry has the same composition before and after veraison, the question remains as to
the factors that trigger the onset of veraison. ABA has been previously reported to play an
Chapter 3: Irrigation and pruning effects on yield 52
important role in triggering veraison (DaPeng et al. 1997); ABA is translocated pre-veraison
from grapevine leaves and accumulates in berries (Antolin et al. 2003). This suggests PRD
may encourage the onset of veraison by the induced synthesis of ABA in the dry rootzone.
Sugar maturation was delayed by MIN in 2000-01 probably because of strong sink
competition due to high crop levels. Other researchers have reported delays in fruit maturity
due to light pruning levels (Sommer and Clingeleffer 1993; Poni et al. 1994; Reynold and
Wardle 2001; Naor et al. 2002). Delays in veraison and maturation were also observed for
SD in 2001-02, which may be attributed to intensive vegetative growth of shoot apices
induced by high irrigation inputs, as was shown by Freeman et al. (1980), Bravdo et al.
(1985) and Dry et al. (1999). No treatment effects on sugar accumulation were observed in
2002-03 when yield was not significantly different between pruning treatments. Sugar
accumulation increased at a faster rate in seasons 2001-02 and 2002-03 compared to 2000-
01. This may be attributed to the reduced total leaf area in the first season, as a result of
very high temperatures in December 2001 causing severe leaf senescence at fruit-set. The
large leaf area reduction, which occurred prior to veraison, may have resulted in a source:
sink imbalance. It has been shown that a reduction in the source of assimilation (i.e. leaves)
can result in a delay of the onset of veraison and the rate of maturation (Howell 2001).
3.4.3 Pruning effect on yield components
The change in vine balance and increased sink size of light pruning levels had an important
role on determining yield, bunch weight, berry weight and berry number. The conversion of
pruning treatments from MECH to MIN and SPUR during winter dormancy in 2000 affected
bunch numbers on vines in the subsequent season. MIN increased the number of nodes by
retaining previous season’s canes and therefore increased number of bunches per vine. A
two-fold difference in bunch number.vine-1 was observed in season 2000-01 for MECH
relative to SPUR and a further two-fold difference for MIN to MECH. These results agree
with those reported for manually pruned, mechanically hedged and minimally pruned
Chancellor vines in British Colombia by Reynolds and Wardle (2001). The increased
reproductive sink size of MIN and MECH vines was counter-balanced by increased total
leaf area.vine-1 and reductions in bunch weight, berry weight and berry number.bunch-1.
Bunch weight and berry weight were significantly reduced by MIN and MECH pruning
Chapter 3: Irrigation and pruning effects on yield 53
treatments compared SPUR in response to high bunch numbers. As a consequence of the
reduced bunch and berry weights by MIN, there was no significant difference in the mean
yield with MECH and mean yield was only 24% lower for SPUR, despite a 74% reduction
in bunch number per vine. The reduction in reproductive growth of light pruning treatments
may be attributed to increased competition for photo-assimilates among reproductive sinks
(berries). Also reductions in flower numbers and/or fruit set may have contributed to the
lower bunch weights and berry number.bunch-1 found on MECH and MIN vines, however
these measurements were beyond the scope of this project.
Large seasonal variation in the number of bunches per vine was observed over the three
experimental seasons, which had direct repercussions on other yield components. Bunch
number.vine-1 was reduced for all treatments in 2002-03 compared to the first two seasons.
As a result of the low bunch number.vine-1 and consequently reduced carbohydrate
partitioning in the final experimental season, bunch weight and berry weight increased for
MIN and MECH vines relative to the previous seasons. Berry number.bunch-1 was also
increased in the final season. This suggests flower number and/or fruit set were greater,
which corresponds to favourable weather conditions at the appropriate reproductive
phenological stages (i.e. flowering and fruit set). Freeman et al. (1979) also reported greater
seasonal variation in fruitfulness (as determined by bunches per shoot) than treatment
response in irrigated and non-irrigated Shiraz vines of four different pruning levels.
3.4.4 PRD influence on yield components
The application of PRD irrigation restricted berry size and as a consequence, yield penalties
were incurred over the three experimental seasons. Previous studies on PRD have generally
shown no yield loss for both potted and field-grown vines compared to control irrigation
treatments, as vine water status is maintained by irrigating the wet side of the vine but a
biochemical response to water stress occurs (Dry et al. 1996, 1999; Loveys et al. 1998).
This would suggest PRD imposed a limitation in water availability during the phase of berry
expansion, particularly when combined with pruning treatments with high bunch numbers
(i.e. MECH and MIN). As a result, the biochemical synthesis of ABA triggered by PRD, in
response to water-stress would not have been separated from the physical effects of reduced
water availability. However, physiological data presented in Chapter 5 clearly shows leaf
Chapter 3: Irrigation and pruning effects on yield 54
water potential was maintained by PRD throughout the season. Therefore, PRD produced a
water-stress response whilst maintaining plant-water status compared to SD irrigation.
Alternatively, PRD could have induced a hormonal or chemical response to a pre-veraison
water deficit, which may have reduced pericarp volume and restricted berry expansion by
modifying the structural properties of cell components and limiting subsequent enlargement
of pericarp cells, as shown by Ojeda et al. (1999, 2001).
Over the three seasons, the only interactive effect between irrigation and pruning treatments
was on berry weight. The combination of PRD and MIN restricted berry size in each season
compared to the other combined irrigation and pruning treatments. This indicates the
combination of increased sink size, change in vine balance by early canopy development
and the water-stress response of PRD all culminated to result in severe berry size reductions.
However, SPUR vines were more sensitive to the application of PRD, as shown by the large
differences in berry size and final yield compared to SPUR vines irrigated by SD. The
sensitivity of SPUR vines to PRD may be related to the relatively large initial berry size and
high water demands for rapid vegetative and reproductive growth at flowering and fruit set
(refer to section 3.3.1). If PRD indeed reduces pericarp volume and modifies cell structural
properties, it would be expected that a more significant response would occur on rapidly
expanding berries with a greater surface area, as was the case for berries produced by SPUR
vines.
3.4.5 Treatment effects on vine balance
The balance between vegetative and reproductive growth of vines was assessed as a ratio of
total leaf area to fruit produced per vine. Total leaf area required to mature one gram of fruit
mass varied between pruning levels, as determined by leaf area index. MECH significantly
lowered LA:F compared to SPUR over the three seasons. Therefore, SPUR vines had
greater vegetative growth compared to reproductive growth, which may produce within-
canopy shading of fruit and consequently undesirable “vegetative” characteristics in the
wine (Allen et al. 1996). However, the low crop loads of SPUR vines may have also
influenced the higher LA:F than simply differences in canopy size between the pruning
systems. Interestingly, MIN vines produced an intermediate LA:F ratio. Thus, vegetative
and reproductive growth was greater on MIN vines compared to MECH vines. This may be
Chapter 3: Irrigation and pruning effects on yield 55
the result of maintaining wood at pruning on MIN vines to create a large permanent canopy
structure. Also, more vegetative growth and potentially greater photosynthetic capacity
may have been required to sustain and ripen the larger crop produced on MIN vines. Given
that fruit produced on MECH and MIN vines reached optimal sugar maturity (24 °Brix), the
smaller total leaf area was sufficient to produce sugar-ripe fruit. This suggests the reduced
total leaf area of MECH and MIN pruning systems was more efficient in carbohydrate
production for sugar accumulation in berries than the SPUR vines with larger total leaf area.
There were no irrigation effects on the ratio of vegetative growth to reproductive growth but
PRD generally increased LA:F relative to SD. This was an indication of the reduced yield on
PRD vines since total leaf area was less for PRD vines than SD vines. Hence the balance
between canopy and fruit of both PRD and SD was sufficient to maintain and ripen the crop
to an acceptable standard. No significant interactions were found for LA:F, and all
treatments produced grapes that met industry-recognised sugar concentrations despite LA:F
values ranging from 14.4 cm2.g (SD + MECH) to 21.9 cm2.g (PRD + SPUR). The large
range of LA:F for the different irrigation and pruning combinations suggests cv. Shiraz has
the capacity to synthesise sufficient carbohydrates or mobilise carbohydrates stored in wood
to ripen large cropping levels.
3.4.6 Improvements in water use efficiency caused by PRD
Water use efficiency was influenced by treatments that reduced water inputs (PRD) and
increased yield (MIN and MECH). WUE was significantly improved by PRD each season,
which agrees with previous studies (Dry et al. 1996; Düring et al. 1996). Loveys et al.
(2000) reported the WUE of PRD irrigated Cabernet Sauvignon, Shiraz and Riesling
varieties were doubled, in conjunction with no yield penalties relative to control treatments.
The large increase in WUE by PRD irrigation has major environmental and economic
benefits. Australia’s water resources are limited and currently restrictions on water use from
the River Murray for irrigation purposes are enforced to maintain water flow and reduce
environmental impact of soil salinisation. As a result, average vineyard irrigation costs have
increased and expansion capacity has reduced. Therefore the application of 50% of irrigation
water by PRD can potentially reduce production costs, reduce the impact of soil salinisation
Chapter 3: Irrigation and pruning effects on yield 56
by decreasing the amount of water percolating into the ground water table and allow for
further vineyard expansion.
3.5 CONCLUSIONS
a) The combination of PRD + MIN reduced the “source-sink” carbohydrate relationship by
increasing the number of potential sinks (bunches per vine) whilst maintaining the same
level of vegetative biomass as the other combined irrigation and pruning treatments.
b) Pruning level had an overriding effect on canopy development, shoot growth and
maximum leaf area. Canopies of MIN vines developed faster and reached maximum
size sooner than SPUR and MECH due to the higher bud numbers retained at winter
pruning.
c) PRD irrigation did not affect primary shoot growth but total leaf area.vine-1 was reduced
later in the growing season. This differs from previous PRD studies (Dry and Loveys
1998; Loveys et al. 1998) and suggests PRD had a transient effect rather than a
permanent effect on canopy development.
d) The combined treatments influenced cell division and water accumulation in berries
from fruit set through to veraison. PRD + MIN produced the smallest berries with the
lowest sugar concentrations on the same calendar day. However, treatments did not
have an effect on cell expansion and solute accumulation (predominantly diffusible
sugars) after veraison, since berry weight increments and rates of sugar accumulation
were consistent between treatments.
e) The yield response of Shiraz grapevines was dominated by bunch number.vine-1, which
was predetermined by pruning level and climatic conditions during bunch initiation.
The high node number retained on MIN vines at the pruning resulted in bunch numbers
4-fold greater than SPUR vines.
Chapter 3: Irrigation and pruning effects on yield 57
f) PRD reduced berry size, as determined prior to veraison. Since plant-water status was
maintained by PRD (refer to Chapter 5), the restriction in berry size was not due to a
limitation in water availability during cell division but possibly a hormonally-induced
reduction in pericarp volume and pericarp cell expansion.
g) Water use efficiency (t.ML-1) was doubled by the reduced water inputs of PRD and
increased yields of MIN and MECH relative to the low yielding, high water input
treatments (SD + SPUR).
h) MIN increased yield, whilst PRD induced a water-stress response that reduced total leaf
area. Therefore the hypothesis that “The combination of light pruning levels of minimal
pruning with PRD irrigation will improve the “source-sink” carbohydrate relationship
may be accepted.
Chapter 4: Irrigation and pruning effects on fruit and wine composition 58
4 IRRIGATION AND PRUNING EFFECTS ON FRUIT AND WINE COMPOSITION
4.1 INTRODUCTION AND EXPERIMENTAL AIMS
Optimisation of fruit and wine quality is important to sustain the competitiveness of the
Australian wine industry, but to maximise profitability quality must be balanced with yield
and production costs. The relationship between yield and quality is complex, since it
depends on the interactions between external climatic and cultural factors (Jackson and
Lombard 1993). The effects of viticultural management strategies on yield and fruit
composition have been extensively studied with diverse results, given the large variation in
climate, cultivars, irrigation regimes and canopy management (Freeman et al. 1983; Bravdo
et al. 1985a,b; Bravdo and Hepner 1987; Rojas-Lara and Morrison 1989; Sommer and
Clingeleffer 1993; Reynolds et al. 1994; Dry et al. 1996; Naor et al. 2002). Some
viticultural strategies employed to improve fruit and wine composition are associated with
yield reductions, e.g. regulated deficit irrigation (RDI) and bunch thinning. Yet, other
management strategies may increase or maintain yield with either no effect or improvements
on fruit specification, e.g. minimal pruning and partial rootzone drying (PRD). The
influence of viticultural management on resultant fruit composition is dependent on changes
in grapevine photosynthetic capacity (Smart and Coombe 1983; Matthews and Anderson
1988; Williams and Matthews 1990), berry size (Clingeleffer 1983; Bravdo et al. 1985b),
canopy microclimate (Smart and Robinson 1991; Allen et al. 1996) and/or vine vigour (Dry
1997).
The benefits of irrigation for fruit and wine quality have been questioned in the literature.
This has resulted in the lack of a uniform hypothesis because of the disparity in irrigation
regimes, irrigation application method, environment and cultivar (Hardie and Considine
1976; Freeman et al. 1983; van Zyl 1984). Irrigation primarily alters the water status and
photosynthetic capacity of vines, which may result in greater sugar accumulation in berries
(Matthews and Anderson 1988; Poni et al. 2000). Increased plant water status can stimulate
shoot vigour and alter canopy microclimate that in turn, leads to excessive shading of
bunches. This may have a negative influence on quality by lowering total soluble solids,
anthocyanin and phenolic concentrations in berries and produce ‘herbaceous’ characteristics
in wine (Smart and Robinson 1991; Allen et al. 1996; Esteban et al. 2001). However,
Chapter 4: Irrigation and pruning effects on fruit and wine composition 59
grapevine vigour has been controlled through the stimulus of a biochemical water stress
response by partially drying the rootzone (PRD) (Dry et al. 2000). Previous PRD pot and
field experiments on grapevines have shown no yield penalties because plant water status is
maintained by irrigating one half of the vine root system, while the other half dries out (Dry
et al. 1996; Dry 1997; Loveys et al. 1998). In addition, PRD may enhance anthocyanin
concentration by a reduction in bunch shading and/or by increasing the exocarp to juice ratio
(Dry 1997). The effect of PRD on wine quality requires evaluation, as it does not appear to
have been documented to date.
Similarly, the effects of canopy management on fruit and wine composition are varied in the
literature, given the range of pruning techniques, trellising, crop level, climate and cultivar
(Freeman and Kliewer 1983; Morris and Cawthon 1982; Poni et al. 2000; Sommer and
Clingeleffer 1993). Pruning level has a large effect on crop level and subsequently, fruit and
wine quality (Reynolds et al. 1994). Light pruning levels, as achieved by mechanical
hedging or minimal pruning, produce higher crop levels than severe pruning treatments,
such as spur pruning, since a greater number of nodes are retained at winter pruning.
Reynolds and Wardle (2001) showed light pruning levels reduced fruit quality by increasing
yield and pH and lowering sugar concentration and titratable acidity when compared to
severe pruning levels of Chancellor grapes. In contrast, light pruning by mechanical
hedging and minimal pruning has been found to improve fruit quality (tartrate to malate
ratio, phenolic and anthocyanin concentration) and wine spectral parameters by increased
bunch exposure and reduced berry size, when adequate sugar levels were reached in both hot
and cool climates (Clingeleffer 1992, 2001; Schultz et al. 2001).
Several researchers have investigated the effects of both irrigation and cropping level on
fruit and wine quality by using bi-factorial experiments (Neja et al. 1977; Freeman et al.
1980; Morris and Cawthon 1982; Freeman and Kliewer 1983; Kliewer et al. 1983; Bravdo et
al. 1985a,b;). Neja et al. (1977), Freeman et al. (1980) and Kliewer et al. (1983) reported
crop level had no influence on fruit and wine quality of Vitis vinifera but delays in sugar
accumulation were observed for high crop levels by Bravdo et al. (1985a,b). Water stress or
alternatively, excessive irrigation reduced sugar concentration and pH in the must (Neja et
al. 1977; Freeman et al. 1980). Morris and Cawthon (1982) also showed that irrigation
Chapter 4: Irrigation and pruning effects on fruit and wine composition 60
delayed sugar maturation of cv. Carignane but increased pH and colour compared to no
irrigation.
The aim of this study is to:
1. Determine irrigation and pruning effects on fruit composition, in respect to total
soluble solids, pH, titratable acidity, anthocyanin and phenolic concentration.
2. Evaluate effects of irrigation and pruning treatments on wine composition.
3. Assess the relationship between fruit and wine composition.
4. Assess the relationship between yield components, as discussed in the previous
chapter (refer to section 3.4.3), fruit and wine composition.
Given the potential for irrigation management and pruning techniques to improve fruit and
wine composition irrespective of yield, this study will test the following hypotheses:
a) The effects of irrigation and pruning treatments on fruit and wine composition of cv.
Shiraz will be minimal because vegetative and reproductive growth is balanced.
b) Small berry size will improve fruit and wine composition parameters, as a result of an
increase in exocarp to juice ratio and concentration of solutes in the mesocarp.
4.2 METHODOLOGY
4.2.1 Determination of fruit total soluble solids, pH and titratable acidity
Fruit composition was assessed at harvest on 10 bunches randomly sampled from each of
the harvest vines (see Chapter 3.2.3 for harvest details). All berries were plucked from the
rachis and one hundred berries were randomly selected and weighed; mean berry weight was
calculated. A further 100 berries were sampled and stored at –20°C for analysis of
anthocyanin and phenolic concentrations.
Chapter 4: Irrigation and pruning effects on fruit and wine composition 61
The 100-berry sub-sample was homogenised by hand using a mortar and pestle. Grape juice
was extracted through a 2mm gauge sieve, left to settle for 1 hour and a 1 mL sub-sample
was used for measurement of total soluble solids (TSS, °Brix) using a temperature
compensating PR-101 digital refractometer (Atago Co. Ltd., Tokyo, Japan). A further 30 mL
aliquot was centrifuged for 10 minutes at 3500 rpm and 10 mL of the remaining juice was
used for the measurement of juice pH and titratable acidity (TA) using VIT90 autotitrator
(Radiometer Co. Ltd., Brønshøj, Copenhagen). The pH electrode was calibrated against
buffers of pH 3 and 7 and titratable acidity was determined by titration to an end point of pH
8.3 with 0.100 M NaOH.
4.2.2 Determination of fruit anthocyanin and phenolic concentration
Anthocyanin and phenolic concentrations were determined using the methodology of Iland
(1996). At harvest, a 100-berry sub-sample was collected, its fresh weight recorded and it
was stored at –20°C until analysis. Berry samples were partially thawed at room
temperature 1 hour prior to maceration. Berries were macerated to a consistent mixture of
exocarp, mesocarp and seeds using a Barmix® handheld food blender. A sub-sample of
homogenate (ca. 1.0 g) was weighed, suspended in aqueous ethanol at pH 2 (50% v/v). The
supernatant was mixed by inversion four times during a 1-hour period and centrifuged at
3500 rpm for 10 minutes. An aliquot of supernatant (1.0 mL) was added to 10 mL of 1.0M
HCl, mixed thoroughly and incubated at room temperature for 3 hours. The volume of
remaining supernatant was recorded and added to the total amount.
Absorbance was measured through a cell with a path length of 50 mm at 520 nm (Abs520) for
anthocyanin concentration and 280 nm (Abs280) for phenolic concentration, employing a
Cintra 10e UV-visible spectrophometer (GBC Scientific Equipment Pty. Ltd., Victoria,
Australia). Formulae for the calculation and anthocyanin and phenolic concentrations are
presented in Appendix C.
4.2.3 Small-scale Wine Production
Two replicates of approximately 4 kg of fruit pooled from across the experimental site for
the six treatments were fermented at harvest, using a similar method to Becker and Kerridge
Chapter 4: Irrigation and pruning effects on fruit and wine composition 62
(1972). Grapes were cooled overnight at 4°C and returned to room temperature (20°C)
before being processed through a de-stemmer/crusher (Amos Ltd., Heilbronn, Germany).
The grapes were crushed into 10L polyethylene containers, and 0.1 g/L SO2 (10% w/v
sodium metabisulphite solution) and 0.75 g/L diammonium hydrogen orthophosphate (10%
w/v solution) were added. Tartaric acid was added as required to lower the pH of must to
between 3.40 - 3.55. Thiamine hydrochloride and re-hydrated Lalvin 254D yeast were also
added at a rate of 1 g/L and 0.2 g/L, respectively.
The must was fermented at 25°C for 3 days, plunged twice daily and then pressed by a 30 L
Willmes air-bag press (Willmes Ltd., Bensheim, Germany). The must was transferred to
CO2 filled glass bottles to continue fermenting at 25°C until less than 0.25% sugar remained.
The wine was racked, adjusted to 20 mg/L SO2 (using 10% w/v sodium metabisulphite) and
stored for 14 days at 15°C, after which a second racking occurred and SO2 re-adjustment
was made if required. The wine was cold stabilized for +30 days at 4°C and sterile-filtered
into 375 mL bottles.
4.2.4 Determination of Wine Composition
Wine pH and TA were assessed at bottling, approximately 6-8 weeks after pressing. A 25
mL sample of wine was degassed using a sonicator for 30 minutes from which a 10 mL sub-
sample was diluted with 40 mL distilled water. The pH and TA were measured using a 702
SM Titrino titrator (Metrohom Ltd. Herisau, Switzerland). The pH electrode was calibrated
against buffers of pH 3 and 7 and titratable acidity was determined by titration to an end-
point of pH 8.3 with 0.100 M NaOH. Spectral evaluation of the wine samples was
conducted according to Somers and Evans (1977) (refer to Appendix D) to measure colour
density, colour hue, total anthocyanin concentration, ionised anthocyanin, degree of
ionisation of anthocyanins (α) and total phenolic concentration. Ionised anthocyanins
represent the fraction of anthocyanins present in the coloured form and the degree of ionised
anthocyanins is the percentage of total anthocyanins present in the coloured form.
Chapter 4: Irrigation and pruning effects on fruit and wine composition 63
4.2.5 Statistical Analysis
Fruit and wine composition data were analysed by Analysis of Variance (ANOVA) using
GenStat® 6th Edition (Lawes Agricultural Trust, Rothamsted Experimental Station). All
interactions were balanced and analysed by general ANOVA (Refer to Appendix B for an
example of the ANOVA analysis). The treatment structure was analysed as
Irrigation*Pruning and the blocking structure was Row*Plot. Yield and fruit composition,
yield and wine composition and yield, fruit and wine composition were correlated using the
correlation coefficient (r) to find interrelationships at the 5% significance level. Correlations
were done on treatment means for each season and across all seasons.
4.3 RESULTS
4.3.1 Fruit Total Soluble Solid, pH and Titratable Acidity Results
Berry composition with respect to TSS, pH and TA was predominantly affected by pruning
treatments. As a consequence, the interactions between irrigation and pruning for fruit
analysis were generally insignificant.
Total Soluble Solids
Pruning level affected TSS concentration in seasons 2000-01 and 2002-03 (Table 4.1).
MECH and MIN had lower TSS concentrations overall compared to SPUR (3%). No
irrigation effects were observed. The interaction between irrigation and pruning was
significant for TSS in 2002-03, however the range of TSS concentrations was only 1 °Brix.
The variation between seasons was not a true representation because of the change in
harvest strategy from calendar date in 2000-01 to harvest by maturity level in 2001-02 and
2002-03.
Chapter 4: Irrigation and pruning effects on fruit and wine composition 64
TABLE 4.1: The total soluble solid concentration of berries from vines with integrated irrigation and pruning treatments and seasonal means for 2000-01, 2001-02, 2002-03. Different letters denote significant differences between treatment means for each season (column) and across seasons (rows), as calculated by Fisher’s least significant difference (LSD 5% level). Significant differences between treatments are denoted by *** P<0.001, ** P<0.01, * P<0.05, ns= not significant.
Total Soluble Solids (°Brix) Treatment 2000-01 2001-02 2002-03 Grand Mean Year LSD Season Mean 22.9 24.4 24.5 23.9 *** 0.24 SD 23.1 24.6 24.5 24.0b PRD 22.8 24.1 24.5 23.8a Irrigation ns ns ns ** ns 0.13 SPUR 23.7b 24.5 25.0b 24.4b MECH 22.7a 24.2 24.4a 23.7a MIN 22.4a 24.4 24.1a 23.7a Pruning *** ns *** *** *** 0.23 SD + SPUR 24.0 24.6 25.0bc 24.5e PRD + SPUR 23.5 24.3 25.1c 24.3d SD + MECH 23.0 24.4 24.7bc 24.0c PRD + MECH 22.4 24.0 24.0a 23.5a SD + MIN 22.3 24.7 23.8bc 23.6b PRD + MIN 22.6 24.1 24.4ab 23.7b Irrigation*Pruning ns ns ** * ns 0.55
pH
The difference in pH of berry juice between treatments was low. However, these
differences were significant because of the low level of variation. SPUR increased the pH
of berry juice relative to the other pruning treatments in each experimental season (Table
4.2). Irrigation had a minor effect in season 2002-03; PRD increased pH relative to SD by
1%. The interaction between irrigation and pruning had no significant effect on pH.
Titratable Acidity
The irrigation and pruning effects on juice TA were relatively small and the difference in
mean TA between combined treatments was only ± 0.18 g.L-1 (Table 4.3). However, MIN
increased TA compared to MECH and SPUR in seasons 2000-01 and 2002-03. The effect
of irrigation on TA was negligible. A significant interaction between irrigation and pruning
occurred in season 2001-02. PRD + MECH increased TA compared to all other treatment
combinations.
Chapter 4: Irrigation and pruning effects on fruit and wine composition 65
TABLE 4.2: The pH of berries from vines with integrated irrigation and pruning treatments and seasonal means for 2000-01, 2001-02, 2002-03. Different letters denote significant differences between treatment means for each season (column) and across seasons (rows), as calculated by Fisher’s least significant difference (LSD 5% level). Significant differences between treatments are denoted by *** P<0.001, ** P<0.01, * P<0.05, ns= not significant.
pH Treatment 2000-01 2001-02 2002-03 Grand Mean Season LSD Season Mean 4.00 3.61 3.65 3.75 *** 0.03 SD 3.98 3.64 3.62a 3.75 PRD 4.02 3.59 3.67b 3.76 Irrigation ns ns * ns *** 0.06 SPUR 4.09c 3.62b 3.70c 3.80b MECH 4.00b 3.57a 3.65bc 3.74a MIN 3.91a 3.66b 3.60ab 3.72a Pruning *** * ** ** *** 0.05 SD + SPUR 4.10 3.67 3.67 3.81 PRD + SPUR 4.07 3.56 3.72 3.79 SD + MECH 3.99 3.58 3.62 3.73 PRD + MECH 4.02 3.55 3.68 3.75 SD + MIN 3.84 3.67 3.57 3.69 PRD + MIN 3.96 3.66 3.62 3.75 Irrigation*Pruning ns ns ns ns ns 0.08
TABLE 4.3: The titratable acidity of berries from vines with integrated irrigation and pruning treatments and seasonal means for 2000-01, 2001-02, 2002-03. Different letters denote significant differences between treatment means for each season (column) and across seasons (rows), as calculated by Fisher’s least significant difference (LSD 5% level). Significant differences between treatments are denoted by *** P<0.001, ** P<0.01, * P<0.05, ns= not significant.
Titratable Acidity (g.L-1) Treatment 2000-01 2001-02 2002-03 Grand Mean Year LSD Mean 4.72 4.31 4.02 3.96 *** 0.10 SD 4.71 4.32 4.06 3.96 PRD 4.72 4.34 3.98 3.95 Irrigation ns ns ns ns ns 0.16 SPUR 4.63a 4.23a 3.83a 3.85a MECH 4.63a 4.64b 4.04b 4.05b MIN 4.90b 4.07a 4.18b 3.97b Pruning ** *** *** *** *** 0.17 SD + SPUR 4.63 4.37bc 3.90 3.92 PRD + SPUR 4.63 4.09a 3.76 3.78 SD + MECH 4.62 4.49c 4.08 4.01 PRD + MECH 4.63 4.78d 4.00 4.09 SD + MIN 4.89 3.98a 4.20 3.94 PRD + MIN 4.91 4.14ab 4.17 4.00 Irrigation*Pruning ns * ns ns ns 0.26
Chapter 4: Irrigation and pruning effects on fruit and wine composition 66
4.3.2 Fruit Anthocyanin and Phenolic Concentrations and Content
Anthocyanin and phenolic concentrations were improved by light pruning treatments but the
content of these compounds per berry was influenced by berry size. The combined
irrigation and pruning effects on anthocyanin and phenolic concentrations varied from
season to season.
Anthocyanin Concentration
Anthocyanin concentrations were much higher in 2001-02 than 2000-01 (105%) and 2002-
03 (51%) (Table 4.4 a). A significant difference between pruning technique occurred in
season 2001-02; MIN increased anthocyanin concentration by 8% compared to SPUR.
Irrigation method had no significant effect on anthocyanin concentration, nor did the
combination of irrigation and pruning.
Anthocyanin Content
Anthocyanin content per berry was influenced by the large difference in berry weight
between combined irrigation and pruning treatments (Table 4.4 b). Anthocyanin content
was highest on combined treatments with large berries (e.g. SD + SPUR) and lowest on
treatments with small berries (e.g. PRD + MIN). The reductions in anthocyanin content
associated with PRD were more pronounced when combined with SPUR and MECH.
Phenolic Concentration
Phenolic concentrations were also high in the cool season of 2001-02 (Table 4.5 a).
Differences between pruning treatments were significant in seasons 2001-02 and 2002-03.
MIN increased phenolic concentration relative to MECH (10%) and SPUR (15%) in season
2001-02. MIN and MECH both increased phenolic concentration relative to SPUR in
season 2002-03 by 11% and 6%, respectively. PRD increased phenolic concentration by
14% compared to SD in 2002-03 only. Combined irrigation and pruning treatments had a
significant effect on phenolic concentration in 2003 and over the three seasons. PRD + MIN
and PRD + MECH increased phenolic concentrations, while PRD + SPUR decreased
phenolic concentration.
Chapter 4: Irrigation and pruning effects on fruit and wine composition 67
TABLE 4.4: The anthocyanin a. concentration and b. content of berries from vines with integrated irrigation and pruning treatments and seasonal means for 2000-01, 2001-02, 2002-03. Different letters denote significant differences between treatment means for each season (column) and across seasons (rows), as calculated by Fisher’s least significant difference (LSD 5% level). Significant differences between treatments are denoted by *** P<0.001, ** P<0.01, * P<0.05, ns= not significant.
a. Anthocyanin concentration (mg Anthocyanin.berry mass-1 g) Treatment 2000-01 2001-02 2002-03 Grand Mean Season LSD Season Mean 0.94 1.93 1.42 1.43 *** 0.06 SD 0.93 1.85 1.39 1.39 PRD 0.97 2.00 1.46 1.47 Irrigation ns ns ns ns ns 0.18 SPUR 0.95 1.86a 1.39 1.40 MECH 0.94 1.93ab 1.42 1.43 MIN 0.95 2.01b 1.47 1.47 Pruning ns * ns ns ns 0.11 SD + SPUR 0.92 1.82 1.38 1.37 PRD + SPUR 0.98 1.89 1.41 1.42 SD + MECH 0.93 1.80 1.39 1.37 PRD + MECH 0.94 2.06 1.45 1.48 SD + MIN 0.93 1.96 1.41 1.43 PRD + MIN 0.97 2.04 1.52 1.51 Irrigation* Pruning
ns ns ns ns ns 0.20
b. Anthocyanin Content (mg Anthocyanin.berry-1) Treatment 2000-01 2001-02 2002-03 Grand Mean Season LSD Season Mean 1.14 1.92 1.62 1.56 *** 0.07 SD 1.22 2.07 1.75b 1.66b PRD 1.05 1.79 1.48a 1.45a Irrigation ns ns * * ns 0.16 SPUR 1.22 2.18c 1.73b 1.72c MECH 1.14 1.92b 1.73b 1.60b MIN 1.06 1.62a 1.38a 1.34a Pruning ns *** *** *** *** 0.12 SD + SPUR 1.31 2.43d 1.94 1.89d PRD + SPUR 1.12 1.92bc 1.52 1.53bc SD + MECH 1.24 2.00c 1.80 1.68c PRD + MECH 1.03 1.85bc 1.66 1.51b SD + MIN 1.11 1.63a 1.49 1.38ab PRD + MIN 1.02 1.61ab 1.28 1.30a Irrigation* Pruning
ns *** ns ** ns 0.20
Phenolic Content
Phenolic content was dominated by berry size: large berries produced on vines from the
combined treatment of SPUR and SD had the highest content of phenolics per berry.
Phenolic content was significantly affected by the combination of irrigation and pruning
treatments in 2001-02 and 2002-03 (Table 4.5 b). Treatments which produced the largest
berries had the highest level of phenolics per berry, namely SD + SPUR and SD + MECH.
Chapter 4: Irrigation and pruning effects on fruit and wine composition 68
TABLE 4.5: The a. concentration and b. content of berries from vines with integrated irrigation and pruning treatments and seasonal means for 2000-01, 2001-02, 2002-03. Different letters denote significant differences between treatment means for each season (column) and across seasons (rows), as calculated by Fisher’s least significant difference (LSD 5% level). Significant differences between treatments are denoted by *** P<0.001, ** P<0.01, * P<0.05, ns= not significant.
a. Phenolic Concentration (mg Phenolics.berry mass-1 g) Treatment 2000-01 201-02 2002-03 Grand Mean Season LSD Season Mean 1.04 1.60 1.36 1.33 *** 0.05 SD 1.01 1.54 1.27a 1.28 PRD 1.07 1.64 1.45b 1.38 Irrigation ns ns * ns * 0.19 SPUR 1.06 1.50a 1.21a 1.26a MECH 1.03 1.58a 1.41b 1.34b MIN 1.03 1.73b 1.46b 1.40b Pruning ns ** *** *** *** 0.09 SD + SPUR 1.06 1.53 1.23a 1.28a PRD + SPUR 1.06 1.47 1.19a 1.24a SD + MECH 1.03 1.51 1.29a 1.28a PRD + MECH 1.04 1.65 1.53b 1.41ab SD + MIN 0.96 1.61 1.29a 1.29a PRD + MIN 1.09 1.80 1.62b 1.51b Irrigation* Pruning
ns ns ** ** ns 0.20
b. Phenolic Content (mg Phenolics.berry-1) Treatment 2000-01 2001-02 2002-03 Grand Mean Season LSD Season Mean 1.26 1.59 1.53 1.46 *** 0.06 SD 1.34 1.73 1.59 1.55 PRD 1.17 1.47 1.46 1.37 Irrigation ns ns ns ns ns 0.18 SPUR 1.37b 1.77c 1.51b 1.55b MECH 1.26ab 1.58b 1.72c 1.52b MIN 1.14a 1.39a 1.36a 1.29a Pruning ** *** *** *** *** 0.11 SD + SPUR 1.51 2.05c 1.74b 1.76c PRD + SPUR 1.22 1.50ab 1.28a 1.33a SD + MECH 1.37 1.68b 1.67b 1.57b PRD + MECH 1.14 1.49ab 1.76b 1.46ab SD + MIN 1.14 1.35a 1.37a 1.28a PRD + MIN 1.14 1.42a 1.35a 1.31a Irrigation* Pruning
ns *** *** *** ** 0.20
4.3.3 Relationship between Fruit Anthocyanin Concentration and Temperature
The relationship between mean anthocyanin concentration of all treatments at harvest and
mean daily temperature for the months of December, January and February were examined
over the three experimental seasons. Significant negative correlations between anthocyanin
Chapter 4: Irrigation and pruning effects on fruit and wine composition 69
concentration and January and February mean daily temperatures were observed (Table 4.6).
When daily temperatures were lower than average during maturation period (January to
February), colour concentration in berries was higher.
Table 4.6: Correlation coefficients of mean anthocyanin concentration of all treatments with mean daily temperature for the months of December, January and February for the three experimental seasons, n=3. Bold script represents significance at 1% level, P<0.01.
R2
December Mean Temp (ºC)
January Mean Temp (ºC)
February Mean Temp (ºC)
Anthocyanin Concentration mg/g
-0.930
-0.994
-0.999
4.3.4 Wine pH and Titratable Acidity Results
The pH and TA of the wine produced was largely unaffected by either irrigation or pruning.
Large variation in pH and TA was observed in season 2001-02; wine was significantly
higher in TA and lower in pH than the other two experimental seasons.
Wine pH
A minor pruning effect on wine pH occurred in the first experimental season (Table 4.7).
Wine pH was lower for MIN compared to SPUR (4%) and MECH (4%). SD increased the
pH of the wine in 2001-02 by 2% but no other irrigation effects were recorded. No
interactions between irrigation and pruning treatments were observed.
Titratable Acidity
SD irrigation raised TA in season 2000-01 compared to PRD but no other significant effects
were recorded (Table 4.8) The lack of treatment difference between the wine TA was
expected, since the must was acid adjusted during the wine making process.
Chapter 4: Irrigation and pruning effects on fruit and wine composition 70
TABLE 4.7: The pH of wine from vines with integrated irrigation and pruning treatments and seasonal means for 2000-01, 2001-02, 2002-03. Different letters denote significant differences between treatment means for each season (column) and across seasons (rows), as calculated by Fisher’s least significant difference (LSD 5% level). Significant differences between treatments are denoted by *** P<0.001, ** P<0.01, * P<0.05, ns= not significant.
Wine pH Treatment 2000-01 2001-02 2002-03 Grand Mean Season LSD Season Mean 3.50 3.45 3.58 3.51 *** 0.05 SD 3.49 3.49b 3.58 3.52 PRD 3.52 3.41a 3.59 3.51 Irrigation ns * ns ns ns 0.07 SPUR 3.54b 3.49 3.57 3.53b MECH 3.55b 3.45 3.58 3.52ab MIN 3.41a 3.42 3.61 3.48a Pruning * ns ns * * 0.08 SD + SPUR 3.55 3.56 3.59 3.49 PRD + SPUR 3.54 3.42 3.56 3.52 SD + MECH 3.54 3.47 3.56 3.49 PRD + MECH 3.56 3.43 3.59 3.41 SD + MIN 3.37 3.44 3.59 3.58 PRD + MIN 3.46 3.40 3.63 3.59 Irrigation* Pruning ns ns ns ns ns 0.11
TABLE 4.8: The titratable acidity of wine from vines with integrated irrigation and pruning treatments and seasonal means for 2000-01, 2001-02, 2002-03. Different letters denote significant differences between treatment means for each season (column) and across seasons (rows), as calculated by Fisher’s least significant difference (LSD 5% level). Significant differences between treatments are denoted by *** P<0.001, ** P<0.01, * P<0.05, ns= not significant.
Wine Titratable Acidity (g.L-1) Treatment 2000-01 2001-02 2002-03 Grand Mean Season LSD Season Mean 7.25 8.26 7.77 7.76 *** 0.29 SD 7.61b 8.01 7.70 7.77 PRD 6.89a 8.50 7.83 7.74 Irrigation * ns ns ns ** 0.41 SPUR 7.48 8.17 7.63 7.76 MECH 7.01 8.01 7.86 7.63 MIN 7.25 8.60 7.81 7.89 Pruning ns ns ns ns ns 0.50 SD + SPUR 8.02 7.84 7.49 7.78 PRD + SPUR 6.94 8.50 7.77 7.74 SD + MECH 7.36 8.01 7.84 7.74 PRD + MECH 6.67 8.02 7.88 7.52 SD + MIN 7.45 8.19 7.78 7.80 PRD + MIN 7.06 9.00 7.85 7.97 Irrigation*
ns ns ns ns ns 0.71 Pruning
Chapter 4: Irrigation and pruning effects on fruit and wine composition 71
4.3.5 Wine Spectral Evaluation
Wine spectral parameters were strongly influenced by PRD irrigation. Improvements in
wine colour density, hue, colour and phenolics were generally associated with PRD. Large
seasonal variation was also observed for wine density and anthocyanin and phenolic
concentrations.
Wine Colour Density
Wine colour was significantly improved by PRD compared to SD, by 22% and by 31% in
seasons 2000-01 and 2001-02, respectively (Table 4.9). MECH significantly improved
colour density in 2002-03 relative to SPUR (17%) and MIN (15%). Interestingly, trends in
wine colour density for both irrigation and pruning were reversed in 2002-03 compared to
previous seasons as SD and MECH both significantly improved density. No interaction
effects on colour density were observed for combined irrigation and pruning treatments.
TABLE 4.9: The colour density of wine from integrated irrigation and pruning treatments for season 2000-01, 2001-02, 2002-03 and seasonal means. Different letters denote significant differences between treatment means for each season (column) and across seasons (rows), as calculated by Fisher’s least significant difference (LSD 5% level). Significant differences between treatments denoted by *** P<0.001, ** P<0.01, * P<0.05, ns = non significant.
Wine Colour Density (AU) Treatment 2000-01 2001-02 2002-03 Mean Season LSD Season Mean 8.75 10.36 8.07 9.06 *** 0.72 SD 7.90a 9.03a 8.60b 8.51a PRD 9.60b 11.70b 7.54a 9.61b Irrigation * ** * *** *** 1.02 SPUR 8.75 10.50 7.59a 8.95 MECH 8.05 9.34 8.90b 8.76 MIN 9.46 11.25 7.72a 9.48 Pruning ns ns * ns * 1.25 SD + SPUR 7.75 8.38 8.45 8.19 PRD + SPUR 9.74 12.62 6.74 9.70 SD + MECH 7.08 7.97 9.91 8.32 PRD + MECH 9.01 10.71 7.89 9.20 SD + MIN 8.88 10.73 7.44 9.02 PRD + MIN 10.05 11.77 7.99 9.94 Irrigation* Pruning ns ns ns ns * 1.77
Chapter 4: Irrigation and pruning effects on fruit and wine composition 72
Wine Hue
Wine hue is an indication of the red-brown colouration of the wine. Brighter and more red
coloured wines have lower hue values. On average, wines were brighter and redder in
seasons 2000-01 and 2001-02 compared to 2002-03, particularly for SPUR and MIN
treatments (Table 4.10). PRD irrigation reduced hue by 8% in 2001-02 and by 13% over the
three seasons compared to SD. A significant interaction between irrigation and pruning was
found in 2001-02: PRD reduced hue in wines produced from SPUR and MECH vines but
not from MIN vines.
TABLE 4.10: The colour hue of wine from integrated irrigation and pruning treatments for season 2000-01, 2001-02, 2002-03 and seasonal means. Different letters denote significant differences between treatment means for each season (column) and across seasons (rows), as calculated by Fisher’s least significant difference (LSD 5% level). Significant differences between treatments denoted by *** P<0.001, ** P<0.01, * P<0.05, ns = non significant.
Wine Colour Hue (AU) Treatment 2000-01 2001-02 2002-03 Mean Season LSD Season Mean 0.52 0.51 0.54 0.52 *** 0.01 SD 0.52 0.53b 0.55 0.53b PRD 0.52 0.49a 0.54 0.51a Irrigation ns ** ns *** ** 0.02 SPUR 0.53 0.51 0.56b 0.53 MECH 0.53 0.51 0.52a 0.52 MIN 0.50 0.51 0.55b 0.52 Pruning ns ns ** ns * 0.02 SD + SPUR 0.53 0.55b 0.57 0.55d PRD + SPUR 0.52 0.48a 0.54 0.51ab SD + MECH 0.53 0.54b 0.53 0.53cd PRD + MECH 0.52 0.48a 0.51 0.50a SD + MIN 0.49 0.51ab 0.55 0.51abc PRD + MIN 0.51 0.51ab 0.55 0.52bc Irrigation* Pruning ns * ns ** ns 0.03
Ionised Anthocyanins
The fraction of anthocyanins present in the coloured form was significantly higher in 2001-
02 and 2002-03 relative to 2001-02 (Table 4.11). Ionised anthocyanin content was not
affected by the interaction between irrigation and pruning. However, PRD increased it
compared to SD in 2000-01, 2001-02 and 2002-03 by 22%, 41% and 18% respectively.
MECH and MIN significantly improved ionised anthocyanin concentration in 2002-03
Chapter 4: Irrigation and pruning effects on fruit and wine composition 73
compared to SPUR and MIN had the highest level of ionised anthocyanins over the three
seasons.
TABLE 4.11: The ionised anthocyanin concentration of wine from integrated irrigation and pruning treatments for season 2000-01, 2001-02, 2002-03 and seasonal means. Different letters denote significant differences between treatment means for each season (column) and across seasons (rows), as calculated by Fisher’s least significant difference (LSD 5% level). Significant differences between treatments denoted by *** P<0.001, ** P<0.01, * P<0.05, ns = non significant.
Ionised Anthocyanins (mg.L-1) Treatment 2000-01 2001-02 2002-03 Grand Mean Season LSD Season Mean 83 100 95 93 ** 8.7 SD 75a 83a 87a 81a PRD 91b 117b 103b 104b Irrigation * ** ** *** ns 12.3 SPUR 80 100 78a 86a MECH 74 91 101b 89a MIN 95 109 106b 103b Pruning ns ns ** ** * 15.1 SD + SPUR 70 74 68 71 PRD + SPUR 90 126 89 101 SD + MECH 64 73 92 76 PRD + MECH 84 110 111 102 SD + MIN 90 102 101 98 PRD + MIN 100 115 111 109 Irrigation* Pruning ns ns ns ns ns 21.3
Total Anthocyanins
Total anthocyanin content of wine increased progressively over the three experimental
seasons (Table 4.12). The seasonal differences in total anthocyanin content of the wine
were greater than the irrigation and pruning effects. PRD consistently increased total
anthocyanin content of the wine compared to SD in 2000-01, 2001-02 and 2002-03 by 13%,
15% and 19%, respectively. A pruning effect was only observed in 2000-01: SPUR
improved total anthocyanin content compared to MECH and MIN. An irrigation and
pruning interaction was also observed in 2000-01: PRD significantly increased total
anthocyanin content of SPUR (14%) and MIN (24 %) vines but not of MECH vines.
Chapter 4: Irrigation and pruning effects on fruit and wine composition 74
TABLE 4.12: The total anthocyanin concentration of wine from integrated irrigation and pruning treatments for season 2000-01, 2001-02, 2002-03 and seasonal means. Different letters denote significant differences between treatment means for each season (column) and across seasons (rows), as calculated by Fisher’s least significant difference (LSD 5% level). Significant differences between treatments denoted by *** P<0.001, ** P<0.01, * P<0.05, ns = non significant.
b. Total Anthocyanins (mg.L-1) Treatment 2000-01 2001-02 2002-03 Grand Mean Season LSD Season Mean 458 731 966 719 *** 43.1 SD 430a 679a 883a 664a PRD 487b 784b 1049b 773b Irrigation *** * ** *** * 60.9 SPUR 490b 754 966 737 MECH 447a 704 960 704 MIN 438a 736 972 715 Pruning ** ns ns ns ns 74.6 SD + SPUR 458bc 675 840 658 PRD + SPUR 521d 833 1091 815 SD + MECH 441b 626 876 647 PRD + MECH 454bc 781 1044 760 SD + MIN 391a 736 934 687 PRD + MIN 485cd 737 1010 744 Irrigation* Pruning * ns ns ns ns 105.5
Degree of Ionisation of Anthocyanins (α)
The percentage of total anthocyanins present in the coloured form decreased progressively
over the three seasons as total anthocyanin concentration increased (Table 4.13). A pruning
effect was observed in 2000-01: MIN increased the degree of ionisation of anthocyanins
compared to SPUR and MECH. An irrigation effect occurred in 2001-02 as PRD increased
α compared to SD. No significant interactions between irrigation and pruning were found.
Total Phenolics
A progressive increase in mean total phenolic concentration occurred with each season
(Table 4.14). Irrigation and pruning treatments both had an effect on total phenolics of the
wine in seasons 2000-01 and 2002-03. PRD improved total phenolic concentration in the
wine compared to SD irrigation in both seasons. Whilst, total phenolics were increased by
SPUR relative to MIN and MECH in season 2000-01 and by MIN relative to SPUR and
MECH in season 2002-03. A significant interaction between irrigation and pruning was
observed in 2002-03: PRD increased phenolic concentrations in wine from all three pruning
treatments but to a lesser degree for MIN than SPUR or MECH.
Chapter 4: Irrigation and pruning effects on fruit and wine composition 75
TABLE 4.13: The degree of ionisation of anthocyanins of wine from integrated irrigation and pruning treatments for season 2000-01, 2001-02, 2002-03 and seasonal means. Different letters denote significant differences between treatment means for each season (column) and across seasons (rows), as calculated by Fisher’s least significant difference (LSD 5% level). Significant differences between treatments denoted by *** P<0.001, ** P<0.01, * P<0.05, ns = non significant.
Degree of ionisation of Anthocyanins (%) Treatment 2000-01 2001-02 2002-03 Grand Mean Season LSD Season Mean 18.2 13.5 9.9 13.9 *** 1.69 SD 17.6 12.1a 9.8 13.2a PRD 18.8 15.0b 9.9 14.6b Irrigation ns ** ns * ns 2.39 SPUR 16.3a 13.1 8.1 12.5a MECH 16.5a 12.8 10.6 13.3a MIN 21.8b 14.8 10.9 15.8b Pruning * ns ns ** ns 2.92 SD + SPUR 15.3 11.0 8.1 11.5 PRD + SPUR 17.2 15.1 8.0 13.5 SD + MECH 14.5 11.5 10.5 12.2 PRD + MECH 18.6 14.0 10.8 14.5 SD + MIN 23.1 13.9 10.9 15.9 PRD + MIN 20.5 15.8 11.0 15.8 Irrigation* Pruning ns ns ns ns ns 4.14
TABLE 4.14: total phenolic concentration of wine from integrated irrigation and pruning treatments for season 2000-01, 2001-02, 2002-03 and seasonal means. Different letters denote significant differences between treatment means for each season (column) and across seasons (rows), as calculated by Fisher’s least significant difference (LSD 5% level). Significant differences between treatments denoted by *** P<0.001, ** P<0.01, * P<0.05, ns = non significant.
Total Phenolics (mg.L-1) Treatment 2000-01 2001-02 2002-03 Grand Mean Season LSD Season Mean 44 61 78 61 *** 2.74 SD 42a 58 71a 57a PRD 46b 64 84b 65b Irrigation ** ns *** *** * 3.87 SPUR 47b 62 75a 62ab MECH 42a 57 78ab 59a MIN 43a 65 80b 63b Pruning * ns * * * 4.74 SD + SPUR 44 57 68a 56 PRD + SPUR 50 67 82c 66 SD + MECH 41 53 69a 54 PRD + MECH 43 61 86c 63 SD + MIN 40 64 77b 60 PRD + MIN 46 66 82c 65 Irrigation* Pruning ns ns ** ns ns 6.71
Chapter 4: Irrigation and pruning effects on fruit and wine composition 76
4.4 YIELD AND FRUIT COMPOSITION CORRELATIONS
Season 2000-01
Yield was strongly correlated with the number of bunches per vine in season 2000-01 (Table
4.15a). MIN produced high yield because of a high number of small bunches with less
berries of smaller mean size. The leaf area: fruit ratio (LA:F) was lower for MIN treatments
and water use efficiency (WUE) was greater because yield was higher. Berries were less
mature, TA was greater and pH was lower at harvest on high yielding treatments.
Anthocyanin concentration was negatively correlated with berry weight: smaller berries had
higher anthocyanin levels.
Season 2001-02
The correlation between bunch number and yield was weaker in 2001-02 than the previous
season, but bunch number was still negatively correlated with bunch weight and berry
number (Table 4.15b). Berry number and berry weight positively correlated with bunch
weight. As expected, LA:F was negatively correlated with yield, since yield was the
denominator in the leaf area to fruit ratio. The degree of maturation of berries was related to
WUE: low yielding treatments, such as SPUR had lower WUE and more mature berries at
harvest. Fruit TA and pH were not correlated with yield components. However,
anthocyanin concentration was greater in smaller berries. Anthocyanin and phenolic
concentrations were positively correlated, thus smaller berries should also have higher
phenolic concentrations.
Season 2002-03
Similarly, bunch number did not correlate with yield but negatively correlated with bunch
weight, berry number and berry weight in season 2002-03 (Table 4.15c). Also, berry
number and berry weight dominated bunch weight and there was a positive correlation
between berry number and berry weight. Pruning and irrigation treatments that produced
more bunches with fewer berries per bunch had higher levels of TA and lower pH levels.
Anthocyanin concentrations were higher in smaller berries and anthocyanins and phenolics
were interrelated.
Chapter 4: Irrigation and pruning effects on fruit and wine composition 77
Table 4.15: Correlation coefficients of mean yield components [yield, bunch number.vine-1 (Bunch No.), bunch weight (Bunch Wt.), berry number.bunch-1 (Berry No.), leaf area:fruit (LA:F), water use efficiency (WUE)] and fruit composition parameters[total soluble solids (TSS), pH, titratable acidity (TA), anthocyanin concentration (Antho.) and phenolic concentration (Phenol)] for seasons a. 2000-01, b. 2001-02, c. 2002-03, n=6. Bold script represents significance at 5% level.
a. Yield and Fruit Composition Parameters 2000-01
r Yield (kg)
Bunch No.
Bunch Wt. (g)
Berry No.
Berry Wt. (g)
LA:F (cm2/g)
WUE (t/ML)
TSS (°Brix)
pH TA (g/L)
Antho. (mg/g)
Phenol. (mg/g)
Yield 1.00 0.89 -0.79 -0.86 -0.22 -0.81 0.36 -0.78 -0.97 0.63 -0.14 -0.69
Bunch No. 1.00 -0.93 -0.96 -0.50 -0.57 0.60 -0.79 -0.95 0.91 0.24 -0.40
Bunch Wt. 1.00 0.96 0.71 0.61 -0.81 0.91 0.87 -0.82 -0.47 0.21
Berry No. 1.00 0.51 0.59 -0.65 0.83 0.91 -0.84 -0.28 0.25
Berry Wt. 1.00 0.23 -0.96 0.72 0.39 -0.56 -0.86 -0.14
LA:F 1.00 -0.34 0.77 0.77 -0.20 0.10 0.72
WUE 1.00 -0.83 -0.49 0.58 0.75 0.13
TSS 1.00 0.82 -0.57 -0.34 0.36
pH 1.00 -0.76 -0.08 0.63
TA 1.00 0.45 -0.14
Antho. 1.00 0.45
Phenolics 1.00
b. Yield and Fruit Composition Parameters 2001-02
r Yield (kg)
Bunch No.
Bunch Wt. (g)
Berry No.
Berry Wt. (g)
LA:F (cm2/g)
WUE (t/ML)
TSS (°Brix)
pH TA (g/L)
Antho. (mg/g)
Phenol. (mg/g)
Yield 1.00 0.47 -0.49 -0.29 0.12 -0.85 -0.36 0.43 0.42 0.00 -0.38 0.07
Bunch No. 1.00 -0.90 -0.94 -0.77 -0.02 0.36 0.01 0.48 -0.35 0.54 0.77
Bunch Wt. 0.28 1.00 0.96 0.90 -0.02 -0.51 -0.08 0.08 0.08 -0.69
Berry No. 0.16 1.00 0.76 0.17 -0.39 -0.25 0.02 -0.60 -0.75
Berry Wt. 0.27 1.00 -0.45 -0.65 0.37 0.02 -0.82 -0.69
LA:F 1.00 -0.38 0.31 0.55 -0.35 -0.05 0.58
WUE 1.00 -0.87 -0.26 0.13 0.76 0.73
TSS 1.00 0.62 -0.56 -0.59 -0.45
pH 1.00 -0.56 -0.03 0.36
TA 0.07 1.00 -0.03
Antho. 1.00 0.82
Phenolics 1.00
c. Yield and Fruit Composition Parameters 2002-03
r Yield (kg)
Bunch No.
Bunch Wt. (g)
WUE (t/ML)
pH Antho. (mg/g)
Berry No.
Berry Wt. (g)
LA:F (cm2/g)
TSS (°Brix)
TA (g/L)
Phenol. (mg/g)
Yield 1.00 0.10 0.24 -0.52 0.62 -0.11 0.32 -0.11 -0.83 -0.16 -0.77 -0.22
Bunch No. -0.58 1.00 -0.87 -0.91 -0.82 0.02 0.47 -0.72 0.82 0.76 0.66
Bunch Wt. 0.65 0.47 1.00 0.96 0.94 -0.36 -0.64 -0.63 -0.79 -0.68
Berry No. 1.00 -0.73 0.82 -0.09 -0.49 0.79 0.66 -0.82 -0.73
Berry Wt. 1.00 -0.58 -0.77 0.38 0.26 -0.41 -0.85 -0.61
LA:F 1.00 0.68 0.25 0.58 -0.49 0.41 0.09
WUE -0.01 0.25 0.03 1.00 0.91 0.73
TSS -0.79 -0.30 -0.51 1.00 0.70
pH 1.00 -0.94 -0.13 -0.23
TA 1.00 0.41 0.55
Antho. 1.00 0.88
Phenolics 1.00
Chapter 4: Irrigation and pruning effects on fruit and wine composition 78
Seasons 2001-2003
Treatment means were also pooled for the three seasons to assess the relationships between
yield components and fruit composition parameters (Table 4.16). Yield was strongly
correlated with bunch number and berry number. Treatments with highest bunch numbers
with fewer berries per bunch, such as MIN, produced the highest yield. High bunch number
was associated with low average bunch weight, low berry number per bunch and low
average berry weight. Improved WUE was associated with high bunch numbers and low
bunch and berry weights. Treatments that produced smaller berries as a result of higher crop
level (MIN) or reduced irrigation input (PRD) had lower pH levels and higher anthocyanin
and phenolic concentrations in berry juice. TSS content was correlated with the other fruit
composition parameters. Berries with high TSS invariably had low TA and high pH, high
anthocyanin concentrations and high phenolic concentrations.
Table 4.16: Correlation coefficients of mean yield components [yield, bunch number.vine-1 (Bunch No.), bunch weight (Bunch Wt.), berry number.bunch-1 (Berry No.), leaf area:fruit (LA:F), water use efficiency (WUE)] and fruit composition parameters[total soluble solids (TSS), pH, titratable acidity (TA), anthocyanin concentration (Antho.) and phenolic concentration (Phenol)] for seasons 2000-03, n=18. Bold script represents significance at 5% level.
Yield and Fruit Composition Parameters 2000-03
r Yield (kg)
Bunch No.
Bunch Wt. (g)
Berry No.
Berry Wt. (g)
LA:F (cm2/g)
WUE (t/ML)
TSS (°Brix)
pH TA (g/L)
Antho. (mg/g)
Phenol. (mg/g)
Yield (kg) 1.00 0.75 -0.43 -0.56 -0.06 -0.64 0.42 -0.48 0.14 0.01 0.00 -0.07
Bunch No. 1.00 -0.83 -0.91 -0.34 0.23 -0.61 0.48 -0.19 -0.22 0.08 0.17
Bunch Wt. (g) 1.00 0.95 0.71 0.27 -0.60 0.31 0.15 -0.06 -0.11 -0.16
Berry No. 1.00 0.47 0.27 -0.41 0.42 -0.04 0.08 0.10 0.02
Berry Wt. (g) -0.43 -0.62 -0.65 1.00 0.11 -0.77 -0.21 0.56
LA:F 1.00 -0.06 -0.04 0.50 -0.44 -0.32 -0.25
WUE 1.00 -0.16 -0.40 0.36 0.43 0.38
TSS (°Brix) 1.00 -0.64 0.63 0.80 0.79
pH 1.00 -0.91 -0.94 -0.87
TA 1.00 0.88 0.84
Antho. (mg/g)
1.00 0.98
Phenolics (mg/g)
1.00
Chapter 4: Irrigation and pruning effects on fruit and wine composition 79
4.5 YIELD, FRUIT AND WINE COMPOSITION CORRELATIONS
Season 2000-01
During 2000-01, treatments with high yield and bunch numbers produced more acidic wine
(i.e. wine with a lower pH) as a response to more acidic juice. As a result, less tartaric acid
adjustment was required during the winemaking phase (Table 4.17a). The amount of tartaric
acid added increased with bunch weight, berry weight and ripeness of the berries (TSS).
Small berries produced wine with higher density and ionised anthocyanins. Reductions in
yield by PRD were associated with increased total anthocyanins in the wine.
Season 2001-02
The ratio of LA:F was highly correlated with wine quality in season 2001-02 (Table 4.17b).
High LA:F was associated with high wine density, total anthocyanins, ionised anthocyanins,
phenolics and degree of ionisation of anthocyanins. Total anthocyanin content was
negatively correlated with yield. Again, the reduction in yield by PRD was positively
correlated with colour and flavour components of the wine produced. Larger berries were
associated with higher wine pH.
Season 2002-03
Yield correlated with the amount of tartaric acid added to the wine in season 2002-03. The
higher the yield, the less tartaric acid that was required to increase TA of the wine (Table
4.17c). Berry anthocyanin and phenolics concentrations were positively correlated with wine
pH, probably as a response to bunch number and berry size. Pruning treatments that
produced more bunches consisting of smaller berries had higher anthocyanin and phenolic
concentrations in the berries and also higher wine pH. Wine total anthocyanins and
phenolics were greater on low yielding treatments, e.g. PRD. PRD decreased berry size and
ultimately yield in 2002-03 with all pruning systems. As a result, colour and phenolics of
the fruit was intensified. The reduced volume of water applied by PRD also improved
WUE. Subsequently, WUE was positively correlated with total anthocyanins, ionised
anthocyanins and total phenolics of the wine. Wine ionised anthocyanin concentration was
correlated with berry anthocyanin and total phenolic concentrations. High degrees of
ionisation of anthocyanins were associated with low berry numbers per bunch, low TSS and
high juice TA, as found for MIN vines.
Chapter 4: Irrigation and pruning effects on fruit and wine composition 80
Table 4.17: Correlation coefficients of mean yield components [yield, bunch number.vine-1 (Bunch No.), bunch weight (Bunch Wt.), berry number.bunch-1 (Berry No.), leaf area:fruit (LA:F), water use efficiency (WUE) and fruit parameters [total soluble solids (TSS), pH, titratable acidity (TA) anthocyanin concentration (Antho.) and phenolic concentration (Phenol.) and wine parameters [tartaric acid addition (TA added), wine pH, wine titratable acidity (TA), colour density, hue, total anthocyanin concentration (Total Antho.), ionised anthocyanin (Ionised Antho.), phenolic concentration (Phenolics), degree of ionisation (alpha)] for season a. 2000-01, b. 2001-02 and 3. 2002-03, n=6. Bold script represents significance at 5% level. r Yield and Fruit Composition Parameters 2000-01
Wine Parameters
Yield kg
Bunch No.
Bunch Wt. g
Berry No.
Berry Wt. g
LA:F cm2/g
WUE t/ML
TSS °Brix
pH TA g/L
Antho. mg/g
Phenol. mg/g
TA added -0.67 -0.78 0.96 0.76 -0.65 0.91 0.78 0.86 0.65 -0.91 -0.54 0.27
Wine pH -0.82 -0.92 0.74 0.79 0.35 0.44 -0.37 0.58 0.90 -0.90 -0.14 0.55
Wine TA 0.03 -0.09 0.41 0.16 0.84 0.31 -0.78 0.57 0.09 -0.05 -0.74 -0.15
Density -0.07 0.32 -0.43 -0.86 -0.24 0.19 0.73 -0.33 -0.14 0.56 0.87 0.26
Hue -0.69 -0.80 0.67 0.63 0.53 0.43 -0.49 0.62 0.80 -0.80 -0.26 0.60 Total Antho. -0.85 0.04 0.48 -0.58 0.39 0.53 -0.22 0.67 0.71 -0.26 0.62 0.75
Ionised Antho. 0.16 0.54 -0.60 -0.45 -0.87 0.05 0.78 -0.48 -0.37 0.74 0.81 0.12
Phenolics -0.76 -0.44 0.32 0.47 -0.29 0.66 0.07 0.44 0.58 -0.08 0.67 0.60
Alpha 0.67 0.86 -0.79 -0.73 -0.68 -0.37 0.69 -0.73 -0.79 0.86 0.38 -0.39
r b. Yield and Fruit Composition Parameters 2001-02
Wine Parameters
Yield kg
Bunch No.
Bunch Wt. g
Berry No.
Berry Wt. g
LA:F cm2/g
WUE t/ML
TSS °Brix
pH TA g/L
Antho. mg/g
Phenol. mg/g
TA added -0.41 -0.61 0.65 0.71 0.43 0.20 -0.68 0.59 -0.01 -0.34 -0.45 -0.75
Wine pH 0.29 -0.53 0.72 0.51 0.91 -0.53 -0.74 0.52 0.31 0.26 -0.67 -0.48
Wine TA -0.24 0.51 -0.45 -0.32 -0.66 0.65 0.76 -0.38 0.14 -0.54 0.51 0.61
Density -0.73 0.19 -0.29 -0.06 -0.69 0.93 0.60 -0.37 -0.16 -0.45 0.64 0.33
Hue 0.80 0.02 0.28 0.03 0.62 -0.76 -0.54 0.54 0.55 0.02 -0.65 -0.15
Total Antho. -0.92 -0.14 -0.05 0.19 -0.47 0.91 0.43 -0.38 -0.36 -0.21 0.56 0.09
Ionised Antho. 0.91 0.65 -0.46 -0.76 0.17 -0.32 -0.08 -0.71 -0.26 -0.33 0.69 0.34
Phenolics -0.65 0.27 -0.27 -0.08 -0.65 0.92 0.46 -0.14 0.12 -0.62 0.61 0.37
Alpha -0.56 0.41 -0.52 -0.30 -0.39 0.76 -0.83 0.84 0.77 -0.49 -0.13 0.54
r c. Yield and Fruit Composition Parameters 2002-03
Wine Parameters
Yield kg
Bunch No.
Bunch Wt. g
Berry No.
Berry Wt. g
LA:F cm2/g
WUE t/ML
TSS °Brix
pH TA g/L
Antho. mg/g
Phenol. mg/g
TA added -0.84 -0.42 -0.01 0.09 -0.01 0.52 0.44 0.06 0.70 -0.48 0.14 0.25
Wine pH 0.11 0.76 -0.57 -0.64 -0.59 -0.01 0.57 -0.42 0.84 -0.36 0.57 0.84 Wine TA -0.21 0.46 -0.75 -0.72 -0.61 0.30 0.55 -0.47 -0.21 0.41 0.51 0.55
Density 0.50 -0.19 0.41 0.25 0.51 -0.63 -0.16 0.27 -0.05 0.11 -0.15 0.10
Hue 0.10 -0.19 0.49 0.55 0.21 0.04 0.06 0.75 0.37 -0.44 0.00 -0.20
Total Antho. -0.84 -0.08 -0.27 -0.05 -0.43 0.85 0.82 0.30 0.70 -0.48 0.50 0.35
Ionised Antho. -0.33 0.55 0.81 -0.09 -0.77 -0.75 -0.69 0.35 -0.46 0.39 0.81 0.86
Phenolics -0.82 0.06 -0.39 0.58 -0.22 -0.50 0.76 0.88 0.08 -0.30 0.65 0.57
Alpha 0.30 0.74 -0.75 -0.90 0.72 -0.50 -0.27 0.26 -0.85 -0.73 0.90 0.53
Chapter 4: Irrigation and pruning effects on fruit and wine composition 81
Seasons 2001-2003
Yield was not significantly correlated with wine quality parameters over the three seasons.
However, berry weight was strongly correlated with most of the measured wine quality
parameters (Table 4.18). Small berries resulted in wine with lower pH and hue, higher wine
density, high total and ionised anthocyanins and higher total phenolic concentration.
Treatments with higher WUE improved wine colour (ionised anthocyanins), density, hue
and reduced pH. Fruit composition was strongly associated with wine quality over the three
seasons. The TSS of berry juice was positively correlated with total anthocyanins and
phenolics and negatively correlated with α. Thus more mature berries at harvest were
correlated with higher total anthocyanin and phenolic concentrations in the wine. Fruit pH
correlated with all wine components with the exception of wine hue. A negative
relationship was found between fruit pH and wine TA, total anthocyanins, ionised
anthocyanins and phenolics. In comparison, a positive relationship was found between fruit
TA and wine TA, total anthocyanins and phenolics. Anthocyanin and phenolics
concentration in the berries was positively correlated with wine TA and negatively
correlated with the amount of TA adjustment required by the must. Berry anthocyanin and
total phenolic concentration also correlated highly with total anthocyanins, ionised
anthocyanins and total phenolics in the wine.
r Yield and Fruit Composition Parameters
Table 4.18: Correlation coefficients of mean yield components [yield, bunch number.vine-1 (Bunch No.), bunch weight (Bunch Wt.), berry number.bunch-1 (Berry No.), leaf area:fruit (LA:F), water use efficiency (WUE) and fruit parameters [total soluble solids (TSS), pH, titratable acidity (TA) anthocyanin concentration (Antho.) and phenolic concentration (Phenol.) and wine parameters [tartaric acid addition (TA added), wine pH, wine titratable acidity (TA), colour density, hue, total anthocyanin concentration (Total Antho.), ionised anthocyanin (Ionised Antho.), phenolic concentration (Phenolics), degree of ionisation (alpha)] for seasons 2000-03, n=18. Bold script represents significance at 5% level.
Wine Parameters
Yield Bunch No.
Bunch Wt. g
Berry No.
Berry Wt. g
LA: F WUE °Brix pH TA Antho. mg/g
Phenol. mg/g
TA added -0.30 -0.80 -0.81 -0.85 -0.48 0.46 0.32 0.70 0.48 -0.67 -0.43 0.79 Wine pH -0.40 -0.71 0.65 0.50 0.68 0.22 -0.58 -0.03 0.58 -0.38 -0.44 -0.40
Wine TA -0.03 0.22 0.75 -0.71 0.58 -0.06 0.07 -0.43 -0.02 0.23 0.79 0.81 Density -0.33 0.25 -0.30 -0.02 -0.81 0.25 0.68 0.28 -0.51 0.33 0.57 0.55
Hue 0.14 -0.27 0.39 0.17 0.58 -0.14 -0.53 0.12 0.35 -0.20 -0.25 -0.17
Total Antho. g/L -0.08 0.38 -0.28 -0.01 0.01 0.26 -0.63 0.79 -0.86 0.78 0.95 0.91
Ionised Antho. g/L -0.27 0.31 0.19 -0.37 -0.09 -0.81 0.23 0.72 -0.52 0.35 0.54 0.52
Phenolics g/L -0.27 0.10 -0.05 0.20 -0.68 -0.03 0.40 0.79 -0.80 0.69 0.93 0.91
Alpha 0.20 0.39 -0.43 -0.43 -0.04 0.25 0.27 -0.85 0.51 -0.59 -0.64 -0.63
Chapter 4: Irrigation and pruning effects on fruit and wine composition 82
4.6 DISCUSSION
4.7.1 Pruning Effects on Fruit and Wine Composition
Winter pruning affected fruit yield, as a result of the number of nodes retained per vine at
pruning, but fruit and wine quality were largely unaffected. A significant 3.8-fold increase
in bunch number per vine and 1.3-fold increase in yield were observed through the retention
of nodes by light pruning (MIN) compared to severe pruning (SPUR). However, the effects
of pruning level on fruit composition (i.e. sugar concentration, pH, TA, colour and flavour
concentrations) and wine composition (i.e. pH, TA, colour density, hue, anthocyanin and
phenolic concentrations) were minimal. Pruning had a minor effect on sugar concentration
(TSS) in the first experimental season when vines were harvested by calendar date; berries
from lightly pruned treatments, MIN and MECH, had slightly lower sugar concentrations
than berries from SPUR. Since the rate of sugar accumulation was not significantly
different between pruning treatments (refer to section 3.4.2), this suggests that the initiation
of veraison was delayed by MIN and MECH. Also, the partitioning of carbohydrates
between sinks (berries) was greater for MIN and MECH compared to SPUR since crop
levels were higher. Reynolds and Wardle (2001) also observed delayed fruit maturity and
reduced °Brix in berries from minimally pruned Chancellor vines and attributed this to
greater crop stress due to higher crop levels.
Severe pruning and its associated larger berry size and higher canopy density influenced the
pH and TA of berry juice: SPUR produced berries with higher pH and lower TA compared
to MIN and MECH. This suggests that larger berries had a relatively greater solvent (water)
to solute (sugars and organic acids) ratio, thus greater dilution of solutes per berry. Fruit
from dense, shaded canopies, as found on SPUR vines, have relatively higher K+ juice
concentrations and pH (Botting et al. 1996; Smart 1992). The degree of increase in berry pH
by SPUR compared to MIN (0.08 units) and MECH (0.06 units) was comparable to studies
on ‘Sunbelt” grapes (Striegler et al. 2002) but was unlikely to be of viticultural significance.
The pruning effects on anthocyanin and phenolic concentrations and content were also
associated with berry size. The small berries produced on MIN vines had higher
concentrations of secondary metabolites (anthocyanins and phenolics) than those produced
on SPUR and MECH vines, which may be attributed to an increased surface area to volume
ratio. Increased anthocyanin concentration of berries on MIN vines may also be linked to
Chapter 4: Irrigation and pruning effects on fruit and wine composition 83
improved microclimate and subsequently, greater bunch exposure (Sommer and Clingeleffer
1993). Levels of anthocyanin and phenolics have been positively correlated with the degree
of bunch exposure for grapevines, particularly on field-grown cv. Cabernet Sauvignon
(Carbonneau 1985; Crippen and Morrison 1986; Rojas-Lara and Morrison 1989; Gao and
Cahoon 1994). The results from this study agree with research on cv. Shiraz that showed
high levels of colour and phenolics were associated with small bunches consisting of smaller
berries and higher levels of ripeness (Holzapfel et al. 1999). However, Reynolds and
Wardle (2001) found minimally pruned Chancellor grapevines produced berries with lower
anthocyanin concentration than hand-pruned vines. When secondary metabolite content was
determined on a per berry basis, SPUR had the highest levels because of the larger berry
size. Iland et al. (1996) showed some viticultural management treatments that promote
anthocyanin and phenolic accumulation per berry often increase berry size, thus lower the
surface area to volume ratio and concentration of secondary metabolites.
As expected, the minor pruning effect on wine composition can be directly associated with
those observed on fruit composition. Wine pH and TA were largely unaffected by the level
of pruning and wine spectral parameters reflected the berry anthocyanin and phenolic
concentrations. Wine colour density and colour hue results are comparable to studies on cv.
Shiraz and cv. Cabernet Sauvignon grown in Coonawarra, South Australia (Clingeleffer
1992). However, wine ionised anthocyanin concentration and the percentage of
anthocyanins present in the coloured form (α) were slightly improved by MIN and can be
attributed to the higher anthocyanin concentration in the smaller berries on MIN vines.
Therefore, light-pruning levels produced higher yields and improved wine spectral
parameters (colour and brightness).
4.7.2 Irrigation Effects on Fruit and Wine Composition
Interestingly, PRD had a minor effect on fruit composition but strong effect on wine colour
and flavour parameters. Fruit pH, TA, anthocyanin and phenolic concentration, and phenolic
content were not significantly affected by the irrigation method applied. However,
anthocyanin concentration in the fruit tended to increase with PRD irrigation. This increase
in anthocyanin concentration may have been due to the increase in exocarp to juice ratio of
smaller berry size associated with PRD. This explanation is supported by the fact that
Chapter 4: Irrigation and pruning effects on fruit and wine composition 84
anthocyanin content was lower in berries from PRD irrigated vines, thus it was a
concentrating effect rather than an actual increase in anthocyanins per berry. Bravdo et al.
(1985a), Hepner et al. (1985), Matthews et al. (1990) and Iland (2000) have shown induced
water stress results in decreased berry size, increased berry colour and phenolic
concentration and/or wine colour density and total phenolics. Also, the higher concentration
of anthocyanins in the berries on PRD irrigated vines may be partly associated with
improved bunch exposure, as a result of reduced leaf area (refer to section 3.3.2).
PRD positively affected wine quality, in particular the spectral parameters associated with
colour and flavour. Wine density, total anthocyanin concentration, ionised anthocyanin and
total phenolic concentration of the wine were all improved by PRD. The slightly raised
anthocyanin levels in the smaller berries produced by PRD and increased exocarp tissue
concentration in fermenting must may partially account for the higher concentration in the
wine. However, similar trends in spectral parameters were not observed in wine produced
from the small berries of MIN vines. This suggest small berry size alone, is not a precursor
to improved wine spectral parameters. The question arises as to why large differences in
spectral properties of wine produced from PRD grapes were observed when no significant
irrigation differences in fruit analysis occurred. A previous study on cv. Cabernet Sauvignon
has shown irrigation treatment effects on concentration of anthocyanin and proanthocyanin
in wines were about 50% of those in berries (Kennedy et al. 2002). The difference between
wine spectral parameters and fruit colour and phenolic concentrations may be due to the
poor extraction of anthocyanins and phenolics from berries, co-pigmentation of
anthocyanins or synthesis of anthocyanin compounds in response to PRD. The extraction
and consequently, determination of anthocyanin and phenolic concentration in berry exocarp
and mesocarp can be influenced by the degree and method of maceration of berries, storage
time, defrosting temperature and exposure to oxygen (P. Petrie and N. Cooley, pers. comm.).
Singleton (1972) found extraction efficiency of phenolic compounds from grape exocarp
decreases as juice volume of berries decreases (i.e. small berries). However, no differences
between fruit analysis and wine spectral properties were found for pruning treatments that
also produced small berries (MIN and MECH). This suggest colour and phenolic extraction
from berry exocarp was reflective of concentrations found in the wine. Alternatively, co-
pigmentation of anthocyanins in wine produced from PRD vines may have induced greater
absorbance of coloured pigments (hyperchromic shift) and possibly, a shift in the
wavelength of maximum absorbance (bathochromic shift), producing blue-purple tones in
Chapter 4: Irrigation and pruning effects on fruit and wine composition 85
the wine. Co-pigmentation is due to molecular associations between colour pigments and
co-pigment cofactors (usually non-coloured organic compounds) in solution. Co-
pigmentation accounts for 30% to 50% of the colour of young red wines (Neri and Boulton
1996) and can be influenced by variety and cultural practices (Boulton 2001). Wines made
from different cultivars have specific patterns of cofactors and cofactor concentrations
(Vaadia 1997). Levengood (1996) also found substantial variation in co-pigmentation levels
in Cabernet Sauvignon wine from different vineyard sites subjected to various cultural
practices. This study shows the potential of cultural practices that influence berry size and
flavonoid synthesis, such as irrigation and crop level, to encourage co-pigmentation of the
wine. Further comprehensive studies are required to investigate the effects of cultural
practices on the concentration of co-pigmentation in fruit and wine.
Unfortunately, spectrophotometric assays of anthocyanin content in red wine do not account
for co-pigmentation (Boulton 2001). Colour measurements of wine were conducted using
the methodology of Somers and Evans (1977) in this experiment, which involved bleaching
and ionisation of anthocyanins to estimate total anthocyanin content, degree of ionisation of
anthocyanins and chemical age (ratio between monomeric anthocyanins and polymeric
pigments). Bleaching in the assay for free sulphur dioxide may result in an overestimated
anthocyanin content due to enhanced colour released from the co-pigmented forms
compared to other colour determination techniques (HPLC) (Bakker et al. 1986). Somers
and Evans (1977) acknowledged the existence of co-pigmentation, however its contribution
is omitted from anthocyanin readings in several equations. Further investigation into
anthocyanin separation, identification and quantification is required using HPLC, NMR or
circular dichroism (CD) to determine the contribution of co-pigmentation to total
anthocyanin colour and concentrations and ratios of the major anthocyanin pigments (i.e.
delphinidin, cyanidin, petunidin, peonidin and malvidin), as described by Esteban et al.
(2001).
4.7.3 Irrigation and Pruning Effects on Fruit and Wine Composition
The combination of irrigation technique with pruning level had minor effects on fruit and
wine analysis. SPUR and MECH pruning treatments were more sensitive to PRD irrigation
than MIN, in terms of fruit sugar and secondary metabolite concentrations, and wine spectral
Chapter 4: Irrigation and pruning effects on fruit and wine composition 86
parameters. This was associated with the greater reduction in berry size by PRD on SPUR
and MECH vines relative to MIN vines. Fruit and wine pH and TA levels were not
significantly altered by the interaction between irrigation and pruning treatments, which
agrees with previous bi-factorial studies (Freeman et al. 1980).
Fruit maturity, as determined by TSS concentration chronologically, was slightly reduced by
high crop levels and PRD irrigation, which may have been due to increased partitioning of
carbohydrates between more sinks (bunches) and an insufficient rate of carbon fixation by
photosynthesis over time to allow fruit to ripen. Bravdo et al. (1985a, 1986) have shown
high crop levels can delay ripening of fruit as a result of greater sink demands. However,
previous irrigation studies of vines have also shown a reduction in TSS concentration by
irrigation when berry growth is faster than the increase in sugar accumulation in the berry
and dilution occurs (Freeman et al. 1980; McCarthy et al. 1983; Smart and Coombe 1983;
Bravdo et al. 1985b; van Zyl 1984; Bravdo and Hepner 1987).
Anthocyanin and phenolic concentrations in the berries were much greater in 2001-02 for all
combined treatments than other seasons. This may be due to slow accumulation under mild
summer climatic conditions, as shown by the strong negative correlation with mean daily
December to February temperatures. Kliewer (1970) and Hale and Buttrose (1974) showed
similar negative correlations between anthocyanin concentration in grapes and temperature.
No significant treatment effects were found for anthocyanin concentration of the berries but
phenolic concentration was improved by the combination of PRD and MIN. The increased
exocarp to juice ratio of small berries may explain the increased levels of phenolics.
Anthocyanin and phenolic content were dependent on berry weight: treatments that reduced
berry size (i.e. PRD and MIN) had less secondary metabolites per berry. However, light-
pruning treatments (MIN and MECH) produced more bunches and consequently, more
berries per vine than SPUR. Thus secondary metabolite content was greater for light
pruning treatments when calculated on a per vine basis (data not shown).
When the effects of irrigation and pruning on wine quality were evaluated, it was apparent
that like fruit quality, the treatments had very minimal effect. Wine pH, TA, colour density,
ionised anthocyanin concentration and percentage of anthocyanins present in the coloured
form (α) were not significantly influenced by the interactions between irrigation and
Chapter 4: Irrigation and pruning effects on fruit and wine composition 87
pruning, which agrees with previous findings (Freeman et al. 1980; Bravdo et al. 1985b).
The lack of significant interactions may be attributed to the additive effect of PRD combined
with MIN to improve wine quality, in terms of colour and flavour properties. Wine hue and
total anthocyanin concentrations of the PRD + MIN were better than the other combined
treatments. However, PRD improved both the brightness and total anthocyanin
concentration of SPUR and MECH treatments compared to SD irrigated vines. This may be
the result of co-pigmentation in the wine induced by PRD, as explained in section 4.7.2.
Improvement to canopy microclimate due to decreased shoot vigour by PRD (Dry 1997), in
conjunction with increased bunch exposure by MIN (Sommer and Clingeleffer 1993), may
have also contributed to greater colour and brightness in these wines.
Sensory analysis of the wine produced from each treatment was not included because of the
difficultly involved with quantification due to the subjective nature of the definition of wine
quality. An objective measure of wine quality is required before quantification can occur.
4.7.4 Influence of Yield on Fruit and Wine Composition
Yield has the potential to affect fruit and wine quality directly by crop level, vine balance
and berry size, and indirectly, by rate of ripening and bunch exposure, as reviewed by
Jackson and Lombard (1993). Bunch number was positively correlated with yield and
negatively correlated with each of its components (i.e. bunch weight, berry weight and berry
number). However, bunch number or yield was not significantly correlated with fruit or
wine quality. These findings support other studies conducted on cv. Shiraz, which have
shown poor correlation between yield and fruit quality (Clingeleffer 1992, 1993; Johnstone
et al. 1996; Gray et al. 1997; Holzapfel et al. 1999). Gray et al. (1997) found no
relationship between yield and the value of the commercial wine, however berry colour and
phenolic concentration were negatively correlated with berry size. This suggests the
photosynthetic capacity and subsequent carbohydrate production of cv. Shiraz is sufficient
to adequately ripen and maintain fruit quality at high crop levels, as achieved on minimal
pruned vines. This has important economic implications for grapegrowers, since cv. Shiraz
could sustain greater tonnages of fruit with no apparent wine quality penalties and, in the
case of PRD + MIN treatments, possibly improve colour concentration.
Chapter 4: Irrigation and pruning effects on fruit and wine composition 88
4.7.5 Influence of Berry Size and TSS on Fruit and Wine Composition
The correlation between berry size and both fruit and wine composition was more
significant than that found for yield. Berry size alters the surface to volume ratio, which
consequently affects the balance of extractable exocarp contents (i.e. secondary metabolites)
to mesocarp contents (i.e. water and sugars) (Dry et al. 1999). The size of a berry also
determines the degree of dilution of solutes (sugars and organic acids) to solvent (water) in
the mesocarp of the grape. Therefore, small berries produced by PRD and MIN were
expected to contain higher concentrations of sugar and organic acids. Berry size also
correlated positively with wine quality: small berries were associated with wine that was
more acidic, brighter and had higher colour density and greater anthocyanin (total and
ionised) and phenolic concentration. However, the integrated results showed that PRD had a
greater influence on wine spectral properties than light pruning levels, which suggests small
berry size is an associated response with improved spectral characteristics of wine rather
than a causative effect, as previously reported (Clingeleffer, 1983). As an alternative, PRD
may have induced a biochemical reaction in the wine, such as co-pigmentation, to increase
absorbance of colour pigments and shift maximum absorbance, as discussed in section 4.7.2.
The concentration of sugar (TSS) in berries was strongly correlated with other fruit
compositional parameters: TA, pH and anthocyanin and phenolic concentrations. This
suggests sugar maturity is important to the production of high quality fruit. Holzapfel et al.
(1999) showed similar interactions between TSS and anthocyanin concentrations for cv.
Shiraz grown in a hot climate. Gladstones (1992) suggested that the duration of ripening
might also influence the compositional balance of grapes through the loss of aromatics.
Botting et al. (1996) found lower concentrations of anthocyanins and glycosyl-glucose [G-
G] in berries from vineyards with delayed maturation. Treatments that increase the rate of
ripening may have a greater photosynthetic capacity to synthesise more carbohydrates and
secondary metabolites. In addition, berry anthocyanin and phenolic concentrations
correlated well with total anthocyanins, ionised anthocyanins and total phenolics in the
wine. This is important to Australia’s wine industry, as several leading wine companies have
recently included berry anthocyanin concentration as a payment parameter, as well as TSS
and yield.
Chapter 4: Irrigation and pruning effects on fruit and wine composition 89
4.7 CONCLUSIONS
a) The combined effects of irrigation and pruning treatments on fruit and wine
composition of cv. Shiraz were unlikely to be of viticultural significance. SPUR and
MECH vines were more responsive to PRD than MIN, in terms of fruit sugar and
secondary metabolite concentrations, and wine spectral parameters. This was associated
with the relative berry size reduction by PRD on SPUR and MECH compared to MIN.
b) Light pruning (MIN and MECH) resulted in minor increases in anthocyanin and
phenolic concentrations of fruit and wine compared to severe pruning (SPUR).
c) PRD did not significantly affect fruit composition, however PRD had a strong effect on
wine spectral properties: density, total anthocyanin concentration, ionised anthocyanin
and total phenolic concentration relative to SD. This may be attributed to co-
pigmentation in the wine.
d) Bunch number or yield did not significantly correlate with fruit or wine quality,
however berry size was strongly correlated with fruit and wine quality.
e) Small berries were associated with low pH and high anthocyanin and phenolic
concentrations and wine that was more acidic, brighter and had high colour density and
anthocyanin (total and ionised) and phenolic concentrations.
f) High berry TSS concentration was also correlated with improved fruit TA, pH and
anthocyanin and phenolic concentrations. This indicates high sugar maturity of berries
is important in the production of high quality fruit.
g) The hypothesis that “irrigation and pruning effects on fruit and wine composition will
be minimal because vegetative and reproductive growth was balanced” is accepted. All
treatments reached optimal sugar maturity, which suggests vine photosynthetic capacity
Chapter 4: Irrigation and pruning effects on fruit and wine composition 90
was sufficient to ripen fruit, despite large differences in bunch number and yield
between treatments.
h) The hypothesis that “small berry size will improve fruit and wine composition
parameters, as a result of an increase in exocarp to juice ratio and concentration of
solutes in the mesocarp” is rejected. Integrated data clearly showed that PRD produced
wine spectral changes in association with small berries (possibly due to co-
pigmentation). However small berries produced on MIN vines did not replicate these
improvements in wine spectral properties.
Chapter 5: Physiological response to irrigation and pruning treatments 91
5 PHYSIOLOGICAL RESPONSE TO IRRIGATION AND PRUNING TREATMENTS
5.1 INTRODUCTION AND EXPERIMENTAL AIMS
Sugar accumulation in the berry is an important determinant of fruit quality in cv. Shiraz and
is affected by the photosynthetic capacity of the grapevine. Photosynthesis is controlled by
the degree of opening of stomatal aperture and subsequent uptake of CO2. Photosynthesis
and other gas exchange parameters (stomatal conductance, transpiration and internal leaf
CO2 concentration) are affected by environmental and internal factors, such as light
intensity, vapour pressure deficit, plant water status, cultivar, carboxylation efficiency, crop
load and water deficits (Chaves and Rodrigues 1987; Schultz 2003). Stomatal conductance
is sensitive to changes in plant water status, as determined by leaf or xylem water potential
(Lui et al. 1978; Naor et al. 1994). Osmoregulation of grapevine leaves is an alternate
mechanism to maintain high water status and high rates of leaf gas exchange, associated
with decreasing plant available water (PAW) (Düring 1984; Rodrigues et al. 1993; Schultz
and Matthews 1993). The degree of solute accumulation in leaves can be dependent on
climatic conditions and grapevine variety (Düring and Loveys 1982) and may affect the
stomatal conductance-leaf water potential relationship.
Irrigation can influence both soil water content and plant water status and can result in
drought conditions if insufficient. As a drought response, water-stressed vines close stomata
to regulate transpiration so that sufficient carbon is gained while plant water status is
maintained (Kriedemann and Smart 1971; Naor et al. 1994; Schultz 2003). Long-term or
intensive water deficits can reduce photosynthetic capacity of grapevines, as a consequence
of decreased ribulose biphosphate synthesis, Rubsico activity and carboxylation efficiency
(Escalona et al. 1999). Several studies have indicated an association between abscisic acid
(ABA) and the regulation of stomatal conductance in response to decreasing soil water
content (Zhang and Davies 1989a, 1989b, 1990, 1991; Gowing et al. 1990). Reduction of
water-stress by stomatal closure has the potential to affect carbohydrate production and
sugar accumulation in berries. Partial rootzone drying (PRD) can induce a drought response
by reducing stomatal conductance in a variety of crops, by drying half the rootzone but
maintains plant water status by irrigating the alternate half of the rootzone (Dry and Loveys
1998; Kang et al. 2001; Liu et al. 2001). Since plant water status is maintained by PRD,
Chapter 5: Physiological response to irrigation and pruning treatments 92
typical physical drought stress responses, such as reduced photosynthesis, crop load loss and
delayed sugar accumulation, should be minimised. Recent studies by dos Santos et al.
(2003) and de Souza et al. (2003) showed PRD irrigation (50% of crop evapotranspiration)
of field-grown grapevines generally maintained plant water status close to a fully irrigated
control treatment (100% crop evapotranspiration) but increased water use efficiency, due to
decreased stomatal conductance and maintained carbon assimilation and crop production.
The presence of fruit activates photosynthesis and stomatal conductance in grapevines
(Kriedemann 1971; Chaves 1984; Downton et al. 1987). Manipulation of crop level by
pruning (Sommer and Clingeleffer 1993; Poni et al. 2000; Intrieri et al. 2001) and fruit
thinning (Wünsche et al. 2000; Petrie 2002) can lead to an increase in photosynthetic rate as
source:sink ratios decrease. However the photosynthetic response of grapevine leaves to
crop management does not appear to be consistent in the literature. Poni et al. (1994) found
no significant effects of crop level on gas exchange or plant water use on field-grown
Concord vines and Chaumont et al. (1994) reported no photosynthetic response to changes
in crop load on potted vines. Crop manipulation by winter pruning affects canopy structure
and total leaf area, subsequently altering the source:sink ratio (Sommer and Clingeleffer
1993). If grapevines are near the critical source:sink ratio because of high crop levels, then
the vines may be more susceptible to external stress, such as drought, which can reduce leaf
and vine photosynthesis (Düring and Loveys 1982; van Zyl 1987; Downton et al. 1988).
Alternatively, when crop level is low due to fruit removal or severe pruning, photosynthesis
can be increased by the demands of other sinks, such as rapidly growing shoot tips (Edson
and Howell 1993).
Grapevine photosynthetic capacity can be determined on a single-leaf or whole-canopy
scale. Single-leaf photosynthetic responses do not always reflect those of the whole canopy,
as leaf responses vary with age, position and orientation (Intrieri et al. 1997). However,
assessments of single-leaf photosynthesis have been used extensively for comparative
studies of treatment effects (Naor and Wample 1994; Poni et al. 1994; Gomez-del-Campo et
al. 2002). The environmental and internal factors that affect grapevine stomatal
conductance and photosynthetic capacity also affect the ratio of intercellular CO2 (Ci) and
atmospheric CO2 (Ca) partial pressures. In C3 plants, the ratio between Ci and Ca is related
to discrimination against naturally occurring stable isotope 13C (Farquhar et al. 1982).
Chapter 5: Physiological response to irrigation and pruning treatments 93
Carbon isotope discrimination has been shown to vary between genotypes and water-
stressed grapevines in pot and field trials (Iacono et al. 1993; Gibberd et al. 2002).
Differences in carbon isotope discrimination can arise from changes in the balance between
stomatal conductance and photosynthetic capacity. If a change in carbon isotope
discrimination were due to a variation in photosynthetic capacity per unit area of leaf, a
negative relationship with yield would be expected, as shown in peanuts by Wright et al.
(1994). However, positive relationships between carbon isotope discrimination and yield
have been found for cereal crops (Condon et al. 1987). This indicates that a variation in
stomatal conductance may influence carbon isotope discrimination. As a result, WUE is
increased because the stomatal limitation on transpiration is higher than on photosynthesis.
If carbon isotope discrimination is lowered by increasing photosynthetic capacity whilst
maintaining stomatal conductance, no loss in yield would be expected and WUE would be
improved, as has been also been shown with peanuts (Nageswara Rao and Wright 1994).
The physiological effects of combined irrigation and pruning on cv. Shiraz will be evaluated
in this study to test the following hypothesis:
a) The physiological response of cv. Shiraz will be negatively affected by the interaction
between PRD and light pruning levels, as it nears the critical ‘source:sink’ relationship.
The aims of this study are to:
1. Assess the effects of PRD integrated with three pruning levels on midday leaf gas
exchange and carbon isotope discrimination of cv. Shiraz.
2. Investigate the diurnal response of field grown cv. Shiraz vines irrigated by PRD to
increasing vapour pressure deficit (VPD) under warm climate conditions.
5.2 METHODOLOGY
5.2.1 Midday Leaf Gas Exchange
Ambient leaf gas exchange measurements were conducted on all irrigation by pruning
combinations at midday (1100-1400 h) on cloudless days when air temperature was ≥25°C.
Weather conditions (temperature, °C, relative humidity, % and VPD, kPa) and volumetric
Chapter 5: Physiological response to irrigation and pruning treatments 94
soil water content (θv, %) were determined at midday (12:00 AEDT) for each of the six
midday gas exchange experimental days in 2002 and 2003.
Net photosynthesis (Α), stomatal conductance (gs), transpiration (Τ), internal leaf carbon
dioxide (Ci) and atmospheric CO2 (Ca) were measured using a portable open infrared gas
analyser (CIRAS; PP System, Hitchin, Herts, UK) and fitted to a Parkinson leaf cuvette
operated at 300 mL.min-1. Readings were taken on a leaf area of 2.5 cm2 when steady state
conditions in gas exchange were achieved (approximately 2 minutes). The CO2
concentration (400 µmol.mol-1), solar radiation, temperature and evaporative demand inside
the leaf cuvette were controlled by the CIRAS at ambient conditions. Carbon dioxide and
water vapour concentration differences between inlet and outlet gas circulating through the
leaf chamber and leaf temperature obtained from energy balance equations were used to
calculate leaf area based rates of Α, gs and Τ using the equation of von Caemmerer and
Farquhar (1981). Transpiration efficiency (Α/Τ) was calculated as the ratio of net A to T.
Vapour Pressure Deficit (VPD) was calculated by the Penman equation (Penman 1955),
using relative humidity and air temperature recorded by the weather station.
Eight fully expanded (i.e. the fifth leaf from the shoot tip), sun exposed leaves of close
proximity and similar age, size and thickness were randomly selected on four replicate vines
per treatment, n=32 vines. Midday leaf gas exchange measurements were conducted on 18
and 23 February 2002 and 13, 14 and 16 January and 17 February 2003 and converted to
days after flowering (DAF). Carbon isotope discrimination analysis was determined on
leaves selected for gas exchange measurements, as described in section 5.2.2.
5.2.2 Carbon Isotope Discrimination
The discrimination against 13C (∆) is an indicator of the ratio between intercellular and
atmospheric partial pressure of CO2 (Ci/Ca) and water-use efficiency (WUE) if VPD
between the leaf and surrounding air is constant (Farquhar et al. 1982, 1989; Hubick and
Farquhar 1989). The ∆ of oven dried (80°C for at least 4 days), finely ground (<100 µm)
leaf laminae samples was determined by mass spectrometry. A standard of known carbon
isotope composition was used relative to Pee Dee Belemnite (PDB). ∆ was calculated as
Chapter 5: Physiological response to irrigation and pruning treatments 95
described by Farquhar and Richards (1984), assuming an isotopic composition of air of
7.6% relative to PDB.
5.2.3 PRD vine response to increasing vapour pressure deficit
PRD vine response to increasing VPD throughout the day was assessed on 4 cloudless days
between veraison and harvest when resource (water and carbohydrate) demands were
greatest due to crop production and high VPD. Diurnal gas exchange (Α, gs, T, Ci, Ca, A/T),
leaf water potential (Ψl) and osmotic potential (Ψs) measurements were taken hourly
between 6:00 and 14:00 AEDT on 24 and 25 January and 26 February 2002 and between
6:00 and 18:00 AEDT on 14 February 2003. Gas exchange measurements were conducted
using the CIRAS-1 under ambient conditions as described in section 5.2.1, on four randomly
selected sun exposed, fully expanded leaves from MIN vines irrigated by PRD or SD. MIN
vines were chosen as they had shown the greatest photosynthetic sensitivity to PRD in initial
experiments in season 2000-01.
Immediately following gas exchange measurements, the selected leaf blade was sealed in a
small polyethylene bag to reduce transpiration and the petioles were excised with a razor
blade. Leaf water potential (ΨL) was determined by placing the leaf blade in a pressure
chamber (Soil Moisture Equipment Corp., Santa Barbara, California, USA) and the petiole
was sealed in a silicone gasket, as described by Turner (1988). After ΨL was measured, leaf
blades were wrapped in aluminium foil and stored on dry ice. Leaf osmotic potential (Ψs)
was determined using a vapour pressure Osmometer 5500 (Wescor, Logan, Utah, USA), as
described by Düring (1984).
5.2.4 Statistical Analysis
The main effects and treatment interactions between irrigation and pruning for midday gas
exchange measurements were analysed using generalised analysis of variance (ANOVA) in
the GENSTAT® statistical package. Pruning effects on leaf development were analysed
over the growing period using repeated measures, analysis of variance (ANOVA) in the
GENSTAT® statistical package.
Chapter 5: Physiological response to irrigation and pruning treatments 96
5.3 RESULTS OF IRRIGATION AND PRUNING EFFECTS ON MIDDAY LEAF GAS EXCHANGE
5.3.1 Midday Leaf Gas Exchange for 2002 and 2003 Growing Seasons
Vine physiology at midday was strongly influenced by the application of PRD in both 2001-
02 and 2002-03. PRD reduced gs by 17% and 9 %, Α by 12% and 6% and Τ by 16% and
15% in 2001-02 and 2002-03, respectively. As Ci was not significantly affected by PRD in
either growing season, the sub-stomatal concentration of CO2 may not have been altered by
the reduction in stomatal aperture. Α/Τ was improved by PRD as a direct response to a
greater reduction in Τ rate relative to Α.
Pruning had a minor effect on midday leaf gas exchange. Stomatal conductance (gs), Α and
Τ were higher for MIN compared to MECH or SPUR in 2001-02. No significant differences
were found between pruning treatments in 2002-03 for the measured gas exchange
parameters. Pruning had no effect on Ci or Α/Τ in either season.
Midday gas exchange data was averaged over each season (2 days in 2001-02 and 4 days in
2002-03) to evaluate the effects of the treatments on gs (Table 5.1), Α (Table 5.2), Τ (Table
5.3) and Α/Τ (Table 5.5). Gas exchange was dominated by the reduction in gs by PRD in
both seasons (Table 5.1). MIN increased gs slightly in the first season and, as a result,
significant interactions were found between irrigation and pruning. The rates of gas
exchange were higher in 2002-03, which may be attributed to the timing of measurements
and soil water content.
The interaction between irrigation and pruning had a significant effect on gs, Α and Τ.
SPUR and MECH treatments showed a large response to PRD with reductions in gs, Α and
Τ. Similarly, MECH was influenced by PRD with large reductions in gs and Α in season
2002-03. However, no gas exchange differences were found between SD + SPUR and PRD
+ SPUR in 2002-03. Ci was not affected by imposed treatments for either season, although
the mean results showed a significant reduction by PRD irrigated vines when they were spur
pruned (Table 5.4). Α/Τ was not affected by the interaction between irrigation and pruning
Chapter 5: Physiological response to irrigation and pruning treatments 97
in 2001-02 but it was improved by PRD compared to SD, particularly combined with SPUR
in 2002-03.
gs (mmol.m-2.s-1)
Table 5.1: Mean midday leaf stomatal conductance (gs) of vines with integrated irrigation and pruning treatments and seasonal means for 2001-02, 2002-03. Different letters denote significant differences between treatment means for each season (column) and across seasons (rows), as calculated by Fisher’s least significant difference (LSD 5% level). Significant differences between treatments are denoted by *** P<0.001, ** P<0.01, * P<0.05, ns= not significant.
Treatment 2001-02 2002-03 Mean Season LSD Season Mean 226 351 320 *** 15.7 SD 247b 368b 338b PRD 204a 334a 301a Irrigation *** *** *** ns 22.2 SPUR 215a 364 327 MECH 220a 346 314 MIN 242b 344 319 Pruning * ns ns ns 27.2 SD + SPUR 255b 345 375 PRD + SPUR 176a 352 308 SD + MECH 237b 377 342 PRD + MECH 203a 314 286 SD + MIN 251b 353 327 PRD + MIN 234b 335 310 Irrigation*Pruning ** ns ns ns 38.5
Table 5.2: Mean midday photosynthesis (Α) of vines with integrated irrigation and pruning treatments and seasonal means for 2001-02, 2002-03. Different letters denote significant differences between treatment means for each season (column) and across seasons (rows), as calculated by Fisher’s least significant difference (LSD 5% level). Significant differences between treatments are denoted by *** P<0.001, ** P<0.01, * P<0.05, ns= not significant.
Α (µmol.m-2.s-1) Treatment 2001-02 2002-03 Mean Season LSD Season Mean 13.5 17.3 16.4 *** 0.47 SD 14.4b 17.8b 17.0b PRD 12.7a 16.8a 15.8a Irrigation *** *** *** ns 0.66 SPUR 13.1ab 17.5 16.4 MECH 13.1a 17.2 16.2 MIN 14.4c 17.2 16.5 Pruning ** ns ns * 0.81 SD + SPUR 14.6b 17.5b 16.8cd PRD + SPUR 11.5a 17.5b 16.0b SD + MECH 13.9b 18.5c 17.4d PRD + MECH 12.3a 15.8a 15.0a SD + MIN 14.7b 17.4b 16.7cd PRD + MIN 14.2b 17.0b 16.3bc Irrigation*Pruning ** *** *** *** 1.15
Chapter 5: Physiological response to irrigation and pruning treatments 98
Table 5.3: Mean midday Transpiration (Τ) of vines with integrated irrigation and pruning treatments and seasonal means for 2001-02, 2002-03. Different letters denote significant differences between treatment means for each season (column) and across seasons (rows), as calculated by Fisher’s least significant difference (LSD 5% level). Significant differences between treatments are denoted by *** P<0.001, ** P<0.01, * P<0.05, ns= not significant.
Τ (mmol.m-2.s-1) Treatment 2001-02 2002-03 Mean Season LSD Season Mean 5.70 7.62 7.14 *** 0.26 SD 6.19b 8.24b 7.72b PRD 5.21a 7.01a 6.56a Irrigation *** *** *** ns 0.36 SPUR 5.49a 7.64 7.11 MECH 5.61a 7.56 7.07 MIN 5.99b 7.67 7.25 Pruning * ns ns ns 0.44 SD + SPUR 6.31d 8.23 7.75 PRD + SPUR 4.68a 7.05 6.46 SD + MECH 5.99cd 8.34 7.75 PRD + MECH 5.23b 6.78 6.39 SD + MIN 6.27d 8.14 7.67 PRD + MIN 5.71c 7.19 6.82 Irrigation*Pruning *** ns ns ns 0.63
Table 5.4: Mean midday intercellular CO2 concentration (CI) of vines with integrated irrigation and pruning treatments and seasonal means for 2001-02, 2002-03. Different letters denote significant differences between treatment means for each season (column) and across seasons (rows), as calculated by Fisher’s least significant difference (LSD 5% level). Significant differences between treatments are denoted by *** P<0.001, ** P<0.01, * P<0.05, ns= not significant.
CI (mmol.mol-1) Treatment 2001-02 2002-03 Mean Season LSD Season Mean 228 241 238 *** 2.47 SD 230 242 239 PRD 226 241 237 Irrigation ns ns ns ns 3.50 SPUR 226 243 239 MECH 228 241 237 MIN 229 240 237 Pruning ns ns ns ns 4.28 SD + SPUR 231 245 241b PRD + SPUR 222 240 236a SD + MECH 229 241 238ab PRD + MECH 226 241 237a SD + MIN 229 239 237a PRD + MIN 228 240 237a Irrigation*Pruning ns ns * ns 6.05
Chapter 5: Physiological response to irrigation and pruning treatments 99
Table 5.5: Mean midday transpiration efficiency (Α/Τ) of vines with integrated irrigation and pruning treatments and seasonal means for 2001-02, 2002-03. Different letters denote significant differences between treatment means for each season (column) and across seasons (rows), as calculated by Fisher’s least significant difference (LSD 5% level). Significant differences between treatments are denoted by *** P<0.001, ** P<0.01, * P<0.05, ns= not significant.
Α/Τ (µmol.mmol-1) Treatment 2001-02 2002-03 Mean Season LSD Season Mean 2.41 2.33 2.35 * 0.06 SD 2.34a 2.21a 2.24a PRD 2.48b 2.45b 2.46b Irrigation * *** *** ns 0.09 SPUR 2.42 2.35 2.37 MECH 2.38 2.33 2.34 MIN 2.43 2.32 2.35 Pruning ns ns ns ns 0.11 SD + SPUR 2.33 2.17a 2.21a PRD + SPUR 2.50 2.53c 2.52c SD + MECH 2.34 2.26a 2.28a PRD + MECH 2.42 2.39b 2.40b SD + MIN 2.35 2.21a 2.24a PRD + MIN 2.50 2.43bc 2.45bc Irrigation*Pruning ns * * ns 0.16
A strong curvilinear relationship (R2 = 0.7553, P<0.01) was found between midday Α and gs
for all treatments. Therefore, leaf photosynthetic rate is likely to be a direct response to gs
and thus stomatal aperture size in this experiment (Figure 5.1).
Stomatal Conductance mmo
0 100 200 300 400 500 600 700
Pho
tosy
nthe
sis
umol
m2 s-1
0
5
10
15
20
25
30
y = 7.8881Ln(x) - 28.625R2 = 0.7553
l m-2 -1s
Figure 5.1: Curvilinear relationship between photosynthesis and stomatal conductance for midday measurements of all treatments (R2 = 0.748), P<0.001
Chapter 5: Physiological response to irrigation and pruning treatments 100
5.3.2 Vapour Pressure Deficit and Soil Water Content
Irrigation
Midday temperature of the gas exchange experimental days ranged from 27.8°C (57 DAF)
to 34.6°C (56 DAF) and relative humidity ranged from 27% (56 DAF) to 40% (100 DAF)
(Table 5.6). As a result of high temperatures and low relative humidity, the VPD at 56 DAF
was very high (4 kPa). VPD was calculated to be between 2.5 and 2.6 kPa on all other days
except at 59 DAF when midday temperature was slightly higher. Days after irrigation (DAI)
and days after rainfall (DAR) were calculated for each scheduled experimental day, as these
parameters may have affected θv. Irrigation occurred between three and six days prior to gas
exchange measurements, and irrigation amounts ranged between 18 and 21 mm for SD and
10 and 12 mm for PRD through either the northern or southern drip line. Rainfall was
expected to have a large effect on θv, particularly of the subsoil on 56, 57 and 59 DAF, as 58
mm of rain fell at 43 DAF, which completely refilled the soil profile. However, no more rain
was recorded until late February. Thus, measurements at 91 DAF would not have been
influenced by rain.
Table 5.6: Midday climatic conditions: temperature (T), relative humidity (RH) and vapour pressure deficit (VPD), number of days after an irrigation event (DAI), corresponding amounts of irrigation water applied to SD and PRD treatments, and number of days after a rainfall event (DAR) and amount of rain (mm) for each of the midday gas exchange measurements.
DAF Midday Rainfall T °C %RH VPD DAI SD mm PRD mm DAR mm
56 34.6 27.2 4.0 3 18.0 10.3N 13 58.0 57 27.8 14 33.0 2.5 4 18.0 10.3N 58.0 59 31.9 31.4 3.2 6 18.0 10.3N 16 58.0 91 28.3 35.8 2.5 5 21.0 12.1N 47 58.0 95 29.8 37.4 2.6 6 21.0 12.1S 1 0.2 100 29.4 40.0 2.5 4 21 12.1N 6 0.2
The θv of the surface soil was not influenced by irrigation treatments, prior irrigation or
rainfall events. This may have been due to higher levels of soil evaporation, plant water use
in the upper 20 cm of soil and the predominantly sandy loam soil type. There was little
difference between the surface soil θv of the SD and PRD irrigation treatments, which
ranged from 19 to 20% for SD and 19 to 21% for PRD. Previous irrigation and rainfall
events did not influence the θv of the surface soil (Table 5.7). Water uptake by vine roots in
the surface soil, soil evaporation and infiltration to subsurface soil was high after an
Chapter 5: Physiological response to irrigation and pruning treatments 101
irrigation event, as was demonstrated by the rapid decrease in surface soil θv on the TDR
graphs for both SD and PRD after an irrigation event (refer to section 2.2.3).
DAF
The θv of the subsurface soil (50-70 cm) was affected by irrigation treatment and prior
rainfall events. The subsurface θv was greater for SD irrigation than PRD irrigation. The
range of θv for the subsoil of the SD irrigated rows was 31 to 40%, whereas PRD reduced θv
to a range between 26 to 34%. The subsurface soil was affected by the large rainfall event
(58 mm in 24 hours) on the 31 December 2002, which completely refilled the soil profile.
As a consequence, θv of SD subsurface soil increased to 40% on 56 DAF and proceeded to
decrease until the next irrigation event. The next rainfall event occurred in late February
2002, thus the remaining experimental days were not influenced by rain. The θv of PRD
subsurface soil was also influenced by the large rainfall event on 43 DAF. However, the
increase was not as substantial because the soil profile under PRD irrigation was drier prior
to the rain event.
Table 5.7: Midday volumetric soil water content (θv %) of SD and PRD (north and south side of the vine) of surface (20-40 cm) and subsurface soil (50-70 cm) as measured hourly by TDR probes located adjacent to vines.
Soil Depth SD PRD cm North South
56 20-40 cm 19.8 21.2 20.4 50-70 cm 40.2 33.8 29.7 57 20-40 cm 19.2 20.7 20.4 50-70 cm 37.9 30.8 29.7 59 20-40 cm 18.9 20.2 19.9 50-70 cm 34.4 27.3 28.5 91 20-40 cm 18.9 20.0 19.7 50-70 cm 37.8 26.1 29.8 95 20-40 cm 19.0 19.7 19.4 50-70 cm 30.5 26.3 30.4 100 20-40 cm 18.9 19.7 19.0 50-70 cm 30.5 28.0 27.6
5.3.2 Phenological Effect on Midday Leaf Gas Exchange
The midday photosynthetic capacity (gs, Α, and Τ) of vines was higher at post-veraison (56,
57 and 59 DAF) than a month later at pre-harvest.
Chapter 5: Physiological response to irrigation and pruning treatments 102
Stomatal Conductance
The rate of gs was greater at post-veraison, particularly 59 DAF, than pre-harvest. No
significant differences between irrigation treatments were recorded early in the season,
however PRD decreased gs significantly from 59 DAF through to harvest (Fig 5.2a). Pruning
had minimal effect on gs through out the ripening phase of berry development. However,
MIN reduced gs at 57 and 91 DAF (Figure 5.2b). The interaction between irrigation and
pruning had a significant effect on gs at 57, 91, 95 DAF (Fig 5.2c). At 57 DAF, SD +
MECH had the highest rates of gs, which indicates this treatment was functioning at a higher
rate than all other treatments. Integrated irrigation and pruning treatments did not influence
gs at 59 DAF, since all SD irrigated treatments had higher rates of gs compared to PRD and
pruning had no effect. A large reduction in gs was measured 91 DAF and SD + SPUR and
SD + MECH had a significantly greater rate of gs compared to all other treatments. The
combination of PRD + SPUR and PRD + MECH lowered the gs of compared to all other
treatments at pre-harvest (95 DAF). A similar physiological response was observed 100
days after flowering but the interaction between irrigation and pruning did not significantly
affect gs.
*****
***
***
ns
ns
150
200
250
300
350
400
450
500
550
56 57 59 91 95 100
DAF
g s (m
mol
/m2 /s
)
Post-veraison Pre-harvest
Figure 5.2a: Midday stomatal conductance (gs) of SD ( ) and PRD ( ) irrigation treatments measured on six days between veraison and harvest in seasons 2001-02 and 2002-03. Significant differences at each measurement day are represented by ***P>0.001, **P>0.01, *P>0.05, ns = non significant.
Chapter 5: Physiological response to irrigation and pruning treatments 103
Net leaf photosynthesis (A) steadily decreased from the maximum rate at 59 DAF to harvest.
No irrigation effects were found at 56 or 57 DAF but PRD decreased A from 59 DAF
onwards relative to SD (Figure 5.3a). The photosynthetic response to PRD reflects the
decrease in gs. However, the degree of difference in A between PRD and SD was only small
relative to that of gs. Significant pruning effects occurred at 56, 59 and 95 DAF (Figure
5.3b). MIN had a higher rate of A at 56 and 95 DAF compared to SPUR and MECH. Yet
nsns***
ns
*
ns
150
200
250
300
350
400
450
500
550
56 57 59 91 95 100
DAF
g s (m
mol
/m2 /s
)
Post-veraison Pre-harvest
Figure 5.2b: Midday stomatal conductance (gs) of SPUR ( ), MECH ( ) and MIN ( ) pruning treatments measured on six days between veraison and harvest in seasons 2001-02 and 2002-03. Significant differences at each measurement day are represented by ***P>0.001, **P>0.01, *P>0.05, ns = non significant.
*
ns
ns
**
ns
*
150
200
250
300
350
400
450
500
550
56 57 59 91 95 100
DAF
g s (m
mol
/m2 /s
)
SD+SpurPRD+SpurSD+MechPRD+MechSD+MinPRD+Min
Post-veraison Pre-Harvest
Figure 5.2c: Midday stomatal conductance (gs) of integrated irrigation and pruning treatments measured on six days between veraison and harvest in seasons 2001-02 and 2002-03. Significant differences at each measurement day are represented by ***P>0.001, **P>0.01, *P>0.05, ns = non significant.
Photosynthesis
Chapter 5: Physiological response to irrigation and pruning treatments 104
SPUR had the highest level of A at 59 DAF. The interaction between irrigation and pruning
significantly affected Α after veraison to 91 DAF (Figure 5.3c). The rate of A was generally
reduced by PRD + MECH and PRD + MIN at post-veraison, relative to the other treatments.
SD + SPUR and SD + MECH had amongst the highest rates of Α, which indicates these
treatment were functioning at a higher rate than all other treatments. No significant
treatment effects were observed at 95 and 100 DAF (i.e. pre-harvest).
*****
**
***ns
ns
5
10
15
20
25
56 57 59 91 95 100
DAF
A ( µ
mol
/ m
2 /s)
Post-veraison Pre-Harvest
Figure 5.3a: Midday leaf photosynthesis (A) of SD ( ) and PRD ( ) irrigation treatments measured on six days between veraison and harvest in seasons 2001-02 and 2002-03. Significant differences at each measurement day are represented by ***P>0.001, **P>0.01, *P>0.05, ns = non significant.
ns**ns
*ns*
5
10
15
20
25
56 57 59 91 95 100
DAF
A ( µ
mol
/ m
2 /s)
Post-veraison Pre-harvest
A (µ
mol
/ m2 /s
)
Figure 5.3b: Midday leaf photosynthesis (A) of SPUR ( ), MECH ( ) and MIN ( ) pruning treatments measured on six days between veraison and harvest in seasons 2001-02 and 2002-03. Significant differences at each measurement day are represented by ***P>0.001, **P>0.01, *P>0.05, ns = non significant.
Chapter 5: Physiological response to irrigation and pruning treatments 105
ns ns
***** *
*
5
10
15
20
25
56 57 59 91 95 100
DAF
A ( µ
mol
/ m
2 /s)
SD+SpurPRD+SpurSD+MechPRD+MechSD+MinPRD+Min
Post-Veraison Pre-Harvest
A (µ
mol
/ m2 /s
)
Figure 5.3c: Midday leaf photosynthesis (A) of integrated irrigation and pruning treatments measured on six days between veraison and harvest in seasons 2001-02 and 2002-03. Significant differences at each measurement day are represented by ***P>0.001, **P>0.01, *P>0.05, ns = non significant.
Transpiration
Transpiration decreased progressively from veraison to harvest, with the exception of 59
DAF. PRD reduced T compared to SD from 57 DAF to 100 DAF, with the greatest
reduction occurring at 59 DAF when T rates were highest (Figure 5.4a). By reducing
stomatal aperture and the conductance of CO2 into the leaf and H2O and O2 out of the leaf,
the rate of Α and Τ was reduced by PRD in conjunction with gs. Pruning treatments had
little affect on T from 56 to 91 DAF but MIN increased T slightly relative to SPUR and
MECH at 95 and 100 DAF (Figure 5.4b).
The rate of T was not significantly altered by the integration of irrigation and pruning
treatments at 56 or 59 DAF (Figure 5.4c). The strongest combined treatment effect occurred
at 57 DAF. SD + MECH had the highest rates of Τ, which indicates this treatment was
functioning at a higher rate than all other treatments. No treatment effect was found on 59
DAF because of the dominant irrigation effect (i.e. T was reduced by PRD). A large
reduction in T was measured at 91 DAF for all treatments, particularly those irrigated by
PRD. The interaction between irrigation and pruning lowered the T of PRD + SPUR and
PRD + MECH compared to all other treatments at pre-harvest (95 and 100 DAF). The
reduction in gs had a direct effect on Τ.
Chapter 5: Physiological response to irrigation and pruning treatments 106
Figure 5.4a: Midday transpiration (T) of SD ( ) and PRD ( ) irrigation treatments measured on six days between veraison and harvest in seasons 2001-02 and 2002-03. Significant differences at each measurement day are represented by ***P>0.001, **P>0.01, *P>0.05, ns = non significant
ns
*** ******
***
***
0
2
4
6
8
10
12
56 57 59 91 95 100
DAF
T (m
mol
/ m
2 /s)
Post-veraison Pre-harvest
**
ns
ns
nsns
0
2
4
6
8
10
12
56 57 59 91 95 100
DAF
T (m
mol
/ m
2 /s)
Post-veraison Pre-harvest
Figure 5.4b: Midday transpiration (T) of SPUR ( ), MECH ( ) and MIN ( ) pruning treatments measured on six days between veraison and harvest in seasons 2001-02 and 2002-03. Significant differences at each measurement day are represented by ***P>0.001, **P>0.01, *P>0.05, ns = non significant.
*
ns ***
ns
* ***
0
2
4
6
8
10
12
56 57 59 91 95 100
DAF
T (m
mol
/ m
2 /s)
SD+SpurPRD+SpurSD+MechPRD+MechSD+MinPRD+Min
Post-veraison Pre-harvest
Figure 5.4c: Midday transpiration (T) of integrated irrigation and pruning treatments measured on six days between veraison and harvest in seasons 2001-02 and 2002-03. Significant differences at each measurement day are represented by ***P>0.001, **P>0.01, *P>0.05, ns = non significant.
Chapter 5: Physiological response to irrigation and pruning treatments 107
Internal CO2 Partial Pressure
The Ci simulated the trend in gs from post veraison to harvest. Irrigation had no significant
affect on Ci levels from 56 to 59 DAF but PRD reduced Ci at 91 and 100 DAF relative to SD
(Figure 5.5a). Pruning level had an influence on Ci at 56, 57 and 91 DAF (Figure 5.5b).
SPUR had the highest Ci at 56 and 57 DAF and MECH had the highest level of Ci at 91
DAF. MIN generally had the lowest Ci relative to the other pruning treatments. The
combination of irrigation treatment and pruning level had a significant affect on Ci early in
the ripening phase of berry development but no affect on Ci in the latter part of berry
ripening (Figure 5.5c). SD + MIN lowered Ci at 56 and 57 DAF compared to SD + SPUR
and PRD + SPUR lowered Ci at 59 DAF compared to PRD + MECH.
Figure 5.5a: Midday internal CO2 concentration (Ci) of SD ( ) and PRD ( ) irrigation treatments measured on six days between veraison and harvest in seasons 2001-02 and 2002-03. Significant differences at each measurement day are represented by ***P>0.001, **P>0.01, *P>0.05, ns = non significant.
*******
nsns
ns
200210220230240250260270280290300
56 57 59 91 95 100
DAF
Ci (
mm
ol /m
2 /s)
Post-veraison Pre-harvest
nsns**
ns
*****
200210220230240250260270280290300
56 57 59 91 95 100
DAF
Ci (
mm
ol /m
2 /s)
Post-veraison Pre-harvest
Figure 5.5b: Midday internal CO2 concentration (Ci) of SPUR ( ), MECH ( ) and MIN ( ) pruning treatments measured on six days between veraison and harvest in seasons 2001-02 and 2002-03. Significant differences at each measurement day are represented by ***P>0.001, **P>0.01, *P>0.05, ns = non significant.
Chapter 5: Physiological response to irrigation and pruning treatments 108
Figure 5.5c: Midday internal CO2 concentration (Ci) of integrated irrigation and pruning treatments measured on six days between veraison and harvest in seasons 2001-02 and 2002-03. Significant differences at each measurement day are represented by ***P>0.001, **P>0.01, *P>0.05, ns = non significant.
**nsns
**
ns
200210220230240250260270280290300
56 57 59 91 95 100
DAF
Ci (
mm
ol /m
2 /s)
SD+SpurPRD+SpurSD+MechPRD+MechSD+MinPRD+Min
Post-veraison Pre-harvest
Transpiration Efficiency
The phenological effect on transpiration efficiency (A/T) was minimal throughout the
ripening phase of berry development and did not reflect the negative trend with time of the
other physiological parameters. A/T ranged between 1.6 and 3.1 µmol.mol-1. PRD increased
A/T at 57, 59, 91 and 100 DAF because of the reduction in transpiration by restriction of
stomatal conductance (Figure 5.6a). Pruning effects on A/T were shown after veraison,
although no consistent trends were found (Figure 5.6b). MIN, MECH and SPUR each
increased A/T at 56, 57 and 59 DAF, respectively. The integration of irrigation and pruning
also affected A/T after veraison (Figure 5.6c). SD irrigation combined with SPUR, MECH
and MIN each reduced A/T relative to the other treatments between 56 and 59 DAF.
ns***
***
***
ns
***
0
0.5
1
1.5
2
2.5
3
3.5
4
56 57 59 91 95 100
DAF
A/T
(m
ol /m
mol)
Post-veraison Pre-harvest
Figure 5.6a: Midday transpiration efficiency (A/T) of SD ( ) and PRD ( ) irrigation treatments measured on six days between veraison and harvest in seasons 2001-02 and 2002-03. Significant differences at each measurement day are represented by ***P>0.001, **P>0.01, *P>0.05, ns = non significant.
Chapter 5: Physiological response to irrigation and pruning treatments 109
***
***
ns
ns
ns
0
0.5
1
1.5
2
2.5
3
3.5
4
56 57 59 91 95 100
DAF
A/T
( µm
ol /m
mol
)
Post-veraison Pre-harvest
Figure 5.6b: Midday internal CO2 concentration (Ci) of SPUR ( ), MECH ( ) and MIN ( ) pruning treatments measured on six days between veraison and harvest in seasons 2001-02 and 2002-03. Significant differences at each measurement day are represented by ***P>0.001, **P>0.01, *P>0.05, ns = non significant.
Figure 5.6c: Midday transpiration efficiency (A/T) of integrated irrigation and pruning treatments measured on six days between veraison and harvest in seasons 2001-02 and 2002-03. Significant differences at each measurement day are represented by ***P>0.001, **P>0.01, *P>0.05, ns = non significant.
ns
***
ns
** ns**
0
0.5
1
1.5
2
2.5
3
3.5
4
56 57 59 91 95 100
DAF
A/T
(m
ol /m
mol)
SD+SpurPRD+SpurSD+MechPRD+MechSD+MinPRD+Min
Post-veraison Pre-harvest
5. 4 IRRIGATION AND PRUNING EFFECTS ON CARBON ISOTOPE DISCRIMINATION
The determination of ∆ was influenced by seasonal variation, PRD irrigation and MIN
pruning as a response to stomatal limitation (Table 5.8). PRD irrigation reduced ∆ in 2000-
01, 2001-02 and 2002-3 by 2%, 3% and 3% respectively, presumably as a result of increases
in stomatal limitation. Pruning had no direct effect on ∆ in 2000-01. However, MIN
reduced ∆ in the two following seasons. The interaction between irrigation and pruning had
an effect on ∆ in 2003. Carbon isotope discrimination was reduced by PRD when combined
Chapter 5: Physiological response to irrigation and pruning treatments 110
with SPUR or MECH. However, PRD had no effect on the ∆ of MIN leaves. This
interaction response was similar to the midday transpiration response in 2002-03.
Table 5.8: Mean Carbon Isotope Discrimination (∆) of vines with integrated irrigation and pruning treatments and seasonal means for 2000-01, 2001-02, 2002-03. Different letters denote significant differences between treatment means for each season (column) and across seasons (rows), as calculated by Fisher’s least significant difference (LSD 5% level). Significant differences between treatments are denoted by *** P<0.001, ** P<0.01, * P<0.05, ns= not significant.
∆ Treatment 2000-01 2001-02 2002-03 Mean Year LSD Seasonal Mean 21.1 19.4 19.7 19.6 ** 0.20 SD 21.3b 19.7b 20.0b 19.9b PRD 20.8a 19.2a 19.5a 19.4a Irrigation *** *** *** *** ns 0.28 SPUR 21.2 19.5b 20.1b 19.8b MECH 21.0 19.6b 19.6a 19.6b MIN 21.0 19.2a 19.5a 19.4a Pruning ns ** ** *** ns 0.34 SD + SPUR 21.4 19.7 20.5c 20.2 PRD + SPUR 20.9 19.3 19.6ab 19.5 SD + MECH 21.2 19.9 19.9b 19.9 PRD + MECH 20.9 19.4 19.4a 19.4 SD + MIN 21.2 19.5 19.6ab 19.5 PRD + MIN 20.8 18.8 19.5ab 19.2 Irrigation*Pruning ns ns * ns ns 0.48
The relationship between ∆ and yield was evaluated to determine if stomatal limitation or
increased photosynthetic capacity influenced treatment physiological responses. When all
data was pooled over the three seasons, no significant relationship was found between yield
and ∆ (R2 = 0.07).
5.5 PRD VINE PHYSIOLOGICAL RESPONSE TO INCREASING VAPOUR PRESSURE DEFICIT
5.5.1 Diurnal Increase in Vapour Pressure Deficit
The diurnal physiological response of PRD irrigated vines to increasing VPD was measured
between veraison and harvest in seasons 2001-02 and 2002-03. Climatic data for diurnal
measurement days are presented in Table 5.9 and volumetric soil water content is presented
in Table 5.10. VPD was plotted against time for the four measurement days (Figure 5.7).
Chapter 5: Physiological response to irrigation and pruning treatments 111
Table 5.9: Hourly climatic conditions (Temperature °C, Relative Humidity % and Vapour Pressure Deficit kPa) for each of the diurnal measurement days.
Time 24/1/02 25/1/02 26/2/02 14/2/03 AEDT T °C %RH VPD T °C %RH VPD T °C %RH VPD T °C %RH VPD
6:00 15.9 55.7 0.8 10.4 79.8 0.3 15.3 95.0 0.1 15.9 61.8 0.7
7:00 14.5 62.1 0.6 10.2 81.3 0.2 19.2 89.1 0.2 65.1 14.4 0.6
8:00 16.8 57.9 0.8 14.5 83.9 0.3 23.0 73.8 0.7 18.1 59.3 0.8
9:00 19.1 53.2 1.0 21.9 58.8 1.1 25.9 63.5 1.2 22.1 48.1 1.4
10:00 22.6 28.1 56.9 1.6 47.1 1.4 27.3 44.0 2.0 25.8 40.9 2.0
11:00 26.1 33.6 39.8 2.0 31.6 32.7 3.1 29.4 50.2 2.0 29.7 2.8
12:00 29.3 34.5 2.7 34.5 26.3 4.0 31.0 42.3 2.6 33.3 27.5 3.7
13:00 32.0 29.0 3.4 19.6 32.4 3.1 4.4 36.9 5.0 35.7 35.2 23.4
14:00 33.5 25.3 3.9 38.1 17.4 5.5 33.6 33.2 3.5 35.8 21.4 4.6
15:00 - - - - - - - - - 35.5 21.1 4.6
16:00 - - - 35.5 4.5 - - - - - - 21.9
17:00 - - - 33.8 4.1 - - - - - - 22.2
18:00 - - 24.0 - - - - - - - 31.7 3.6
Table 5.10: Average volumetric soil water contents (θv %) of diurnal measurement days for SD and PRD (north and south side of the vine) of surface (20-40 cm) and subsurface soil (50-70 cm) as measured hourly by TDR probes located adjacent to vines. Diurnal Soil Depth SD PRD cm North South
24/1/02 20-40 cm 20.6 22.4 19.1
50-70 cm 36.7 36.5 29.3
25/1/02 20-40 cm 20.4 20.1 20.8
50-70 cm 34.0 28.7 31.8
26/2/02 20-40 cm 21.9 19.7 25.0
50-70 cm 32.2 26.9 36.3
14/2//03 20-40 cm 32.6 20.0 34.9
50-70 cm 38.3 26.7 34.1
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
5.0
5.5
6.0
6:00 7:00 8:00 9:00 10:00 11:00 12:00 13:00 14:00 15:00 16:00 17:00 18:00
Time AEDT
VP
D K
Pa
24/01/2002
25/01/2002
26/02/200214/02/2003
Figure 5.7: Diurnal change in vapour pressure deficit (VPD, kPa) for four diurnal measurement days.
Chapter 5: Physiological response to irrigation and pruning treatments 112
5.5.2 Diurnal Response of PRD Vines
The photosynthetic capacity of the vines increased rapidly from dawn to between 8:00 and
9:00 AEDT when photosynthetically active radiation (PAR) was >1200 µmol.s-1.m-2. A
rapid increase in Α and gs occurred in the morning and then stabilised (as VPD increased
between 11:00 and 2:00 AEDT) with a tendency to decline slightly in the late afternoon.
The increase in Τ was more gradual throughout the day. However, the rate declined in the
afternoon. The rates of gs, Α and Τ were all reduced by the application of PRD. Ci decreased
rapidly as plants began to transpire in the early morning and stabilised at approximately
10:00 AEDT at a CO2 concentration of 200-250 µmol.mol-1. PRD also lowered the initial Ci
within the leaf but reached equilibrium at the same concentration as the SD vines after 10:00
AEDT. ΨL was measured in conjunction with gas exchange measurements. No irrigation
treatment differences in ΨL were measured throughout the day, although ΨL decreased
(became more negative) as VPD increased during the day. Interestingly, A was maintained
at a maximal rate despite the large reduction of ΨL to values of <-1.5 Mpa during the diurnal
measurement period. Ψs and cell turgor also decreased (became more negative) as VPD
increased during the day. Ψs and turgor were dependent on soil water content. Ψs was lower
and turgidity was greater on PRD vines when soil water content was high (recently
irrigated).
Diurnal measurements conducted on 24 January 2002
Gas exchange measurements were conducted on an hourly basis between 6:00 and 14:00
AEDT on the 24 January 2002. PRD significantly reduced gs throughout the day, with the
exception of measurements taken at 9:00, 10:00 and 13:00 AEDT (Figure 5.8a). Net A and
Τ were also reduced by PRD throughout the day (Figures 5.8b and c). Minimal variability
was recorded for Τ measurements. Thus, treatment differences were observed. Irrigation
strategy did not influence Α, except at 13:00 AEDT when PRD was slightly greater than SD.
Α/Τ was improved by PRD during the morning when VPD was low, as a response to
reduced Τ by PRD (Figure 5.8d). Ci was slightly lower for PRD compared to SD at several
time points throughout the day (Figure 5. 8e).
Chapter 5: Physiological response to irrigation and pruning treatments 113
Pre-dawn ΨL was slightly lower for PRD irrigated vines (-0.75 MPa) compared to SD
irrigated vines (-0.60 MPa) (Figure 5.8f). ΨL declined steadily throughout the day for both
treatments as VPD increased. The imposition of PRD did not affect ΨL, except at 14:00
AEDT when SD vines demonstrated earlier recovery. PRD lowered ΨS but the treatment
difference was predominantly insignificant (Figure 5.8g). The ΨS of the vine leaves
decreased (i.e. became more negative) as VPD increased. As a result of maintained ΨL and
decreased ΨS by PRD, an increase in cell turgor was observed from 8:00 AEDT onwards
(Figure 5.8h).
Figure 5.8a: Diurnal response of PRD on stomatal conductance (gs) on 24 January 2002, ± SEM.
0
50
100
150
200
250
300
350
400
6:00 7:00 8:00 9:00 10:00 11:00 12:00 13:00 14:00
Time AEDT
SD
PRD
Time AEDT
g s m
mol
.m-2.s
-1
0
5
10
15
20
25
6:00 7:00 8:00 9:00 10:00 11:00 12:00 13:00 14:00
Time AEDT
A m
mol
m-2
s-1
SD
PRD
A µm
ol.m
-2.s
-1
Time AEDT
Figure 5.8b: Diurnal response of PRD on photosynthesis (A) on 24 January 2002, ± SEM.
Chapter 5: Physiological response to irrigation and pruning treatments 114
Fi
gure 5.8c: Diurnal response of PRD on transpiration (T) on 24 January 2002, ± SEM.
Figure 5.8d: Diurnal response of PRD on transpiration efficiency (A/T) on 24 January 2002, ± SEM.
0
1
2
3
4
5
6
7
8
9
10
6:00 7:00 8:00 9:00 10:00 11:00 12:00 13:00 14:00
Time AEDT
µ
SD
PRD
0
50
100
150
200
250
300
350
400
6:00 7:00 8:00 9:00 10:00 11:00 12:00 13:00 14:00
Time AEDT
Ci m
mol
mol
-1
SD
PRD
Ci µ
mol
.mol
-1
0
2
4
6
8
10
12
6:00 7:00 8:00 9:00 10:00 11:00 12:00 13:00 14:00
Time AEDT
SD
PRD
Time AEDT
Time AEDT
Time AEDT
T µm
ol.m
-2.s
-1A/
T µm
ol.m
mol
-1
Figure 5.8e: Diurnal response of PRD on intercellular CO2 partial pressure (Ci) on 24 January 2002, ± SEM.
Chapter 5: Physiological response to irrigation and pruning treatments 115
Fi
Figure 5.8f: Diurnal response of PRD on leaf water potential (ΨL) on 24 January 2002, ± SEM.
-2.00
-1.80
-1.60
-1.40
-1.20
-1.00
-0.80
-0.60
-0.40
-0.20
0.00
6:00 7:00 8:00 9:00 10:00 11:00 12:00 13:00 14:00
Time AEDT
Ψ
SD
PRD
-2.00
-1.80
-1.60
-1.40
-1.20
-1.00
-0.80
-0.60
-0.40
-0.20
0.00
6:00 7:00 8:00 9:00 10:00 11:00 12:00 13:00 14:00
Time AEDT
Ψ
SD
PRD
ψs
MPa
ψ
L M
Pa
Time AEDT
gure 5.8g: Diurnal response of PRD on osmotic potential (ΨS) on 24 January 2002, ± SEM.
Figure 5.8h: Diurnal response of PRD on turgor on 24 January 2002, ± SEM.
0.00
0.20
0.40
0.60
0.80
1.00
1.20
6:00 7:00 8:00 9:00 10:00 11:00 12:00 13:00 14:00
Time AEDT
SD
PRD
Time AEDT
MPa
Chapter 5: Physiological response to irrigation and pruning treatments 116
Diurnal measurements conducted on 25 January 2002
VPD was low between 6:00 and 8:00 AEDT on the 25 January 2002. A decrease in gs was
observed for both treatments between 8:00 and 9:00 AEDT. gs then increased to a
maximum rate at 12:00 AEDT, followed by a steady decline as VPD increased (Figure
5.9a). Photosynthesis and Τ were delayed (Figure 5.9b and 5.9c) compared to 24 January
2002, particularly for PRD irrigated vines. The reduction in Α and Τ rates was associated
with lower gs. Α/Τ was relatively low throughout the day with no treatment differences due
to the reduction in Τ by PRD (Figure 5.9d). Ci decreased as gs, Α and Τ increased.
Equilibrium was reached at 10:00 AEDT at a Ci concentration of approximately 230
µmol.mol-1 (Figure 5.9e).
Figure 5.9a: Diurnal response of PRD on stomatal conductance (gs) on 25 January 2002, ± SEM.
Pre-dawn ΨL was slightly higher than for the previous day (-0.5 to –0.6 MPa) due to the
higher relative humidity and lower temperatures at this time (Figure 5.9f). ΨL decreased for
both irrigation treatments as VPD increased during the day. PRD was lower (more negative)
at 11:00 AEDT but no other treatment differences were recorded throughout the day.
Similarly ΨS decreased as VPD increased, with no treatment differences recorded (Figure
5.9g). Turgor increased at 7:00 AEDT due to an increase in ΨL, with PRD irrigated vines
having slightly more turgidity than SD (Figure 5.9h).
0
50
100
150
200
250
300
350
400
6:00 7:00 8:00 9:00 10:00 11:00 12:00 13:00 14:00
Time AEDT
SD
PRD
Time AEDT
g s m
mol
.m-2.s
-1
Chapter 5: Physiological response to irrigation and pruning treatments 117
Figure 5.9b: Diurnal response of PRD on photosynthesis (A) on 25 January 2002, ± SEM.
Figure 5.9c: Diurnal response of PRD on transpiration (T) on 25 January 2002, ± SEM.
0
1
2
3
4
5
6
7
8
9
10
6:00 7:00 8:00 9:00 10:00 11:00 12:00 13:00 14:00
Time AEDT
µ
SD
PRD
0
5
10
15
20
25
6:00 7:00 8:00 9:00 10:00 11:00 12:00 13:00 14:00
Time AEDT
µ
SD
PRD
0
2
4
6
8
10
12
6:00 7:00 8:00 9:00 10:00 11:00 12:00 13:00 14:00
Time AEDT
SD
PRD
Time AEDT
Time AEDT
Time AEDT
A µm
ol.m
-2.s
-1A/
T µm
ol.m
mol
-1T
µmol
.m-2.s
-1
Figure 5.9d: Diurnal response of PRD on transpiration efficiency (A/T) on 25 January 2002, ± SEM.
Chapter 5: Physiological response to irrigation and pruning treatments 118
Figure 5.9e: Diurnal response of PRD on intercellular CO2 partial pressure (Ci) on 25 January 2002, ± SEM. Figure 5.9f: Diurnal response of PRD on leaf water potential (ΨL) on 25 January 2002, ± SEM.
-2.00
-1.80
-1.60
-1.40
-1.20
-1.00
-0.80
-0.60
-0.40
-0.20
0.00
6:00 7:00 8:00 9:00 10:00 11:00 12:00 13:00 14:00
Time AEDT
Ψ
SD
PRD
0
50
100
150
200
250
300
350
400
6:00 7:00 8:00 9:00 10:00 11:00 12:00 13:00 14:00
Time AEDT
µ SD
PRD
-2.00
-1.80
-1.60
-1.40
-1.20
-1.00
-0.80
-0.60
-0.40
-0.20
0.006:00 7:00 8:00 9:00 10:00 11:00 12:00 13:00 14:00
Time AEDT
ΨS M
Pa
SD
PRD
Time AEDT
Time AEDT
Time AEDT
C
i µm
ol.m
ol-1
ψ
s M
Pa
ψL
MPa
Figure 5.9g: Diurnal response of PRD on osmotic potential (ΨS) on 25 January 2002, ± SEM
Chapter 5: Physiological response to irrigation and pruning treatments 119
Diurnal measurements conducted on 26 February 2002
The volumetric soil water content of the subsurface soil was slightly lower on the 26
February 2002 compared to previous measurements, as the preceding irrigation event
occurred 96 hours prior to measurements (refer to Figures 2.5a, b and c). However, VPD
was also lower than the previous diurnal (refer to Figures 5.7). The rate of gs was lower than
for previous diurnals (Figure 5.10a). PRD had lowered gs between 10:00 and 13:00 AEDT
and this lowered Α and Τ (Figures 5.10b and c). The rate of gs increased more for PRD
than SD as VPD increased. Thus, at 13:00 the gs of PRD irrigated vines surpassed SD
irrigated vines and Α and Τ were greater for PRD in the afternoon. SD had a greater Α/Τ in
the morning due to higher A (Figure 5.10d). However by mid-morning, no treatment
differences were observed. No significant differences in Ci were observed between PRD
and SD (Figure 5.10e).
0.00
0.20
0.40
0.60
0.80
1.00
1.20
6:00 7:00 8:00 9:00 10:00 11:00 12:00 13:00 14:00
Time AEDT
SD
PRD
Time AEDT
MPa
Figure 5.9h: Diurnal response of PRD on turgor on 25 January 2002, ± SEM
Pre-dawn ΨL was higher (less negative) than diurnals conducted in January. No treatment
differences were found in the morning for ΨL until VPD reached 1.6 kPa, when PRD had
lowered ΨL (Figure 5.10f). ΨS was not influenced by the imposition of PRD but it was
lower than for previous diurnals (Figure 5.10g). However, cell turgor in the leaves was
reduced by PRD irrigation (Figure 5.10h).
Chapter 5: Physiological response to irrigation and pruning treatments 120
Figure 5.10a: Diurnal response of PRD on stomatal conductance (gs) on 26 February 2002, ± SEM. Figure 5.10b: Diurnal response of PRD on photosynthesis (A) on 26 February 2002, ± SEM.
0
50
100
150
200
250
300
350
400
6:00 7:00 8:00 9:00 10:00 11:00 12:00 13:00 14:00
Time AEDT
SD
PRD
0
5
10
15
20
25
6:00 7:00 8:00 9:00 10:00 11:00 12:00 13:00 14:00
Time AEDT
µ
SD
PRD
g s m
mol
.m-2.s
-1A
µmol
.m-2.s
-1
Time AEDT
0
2
4
6
8
10
12
6:00 7:00 8:00 9:00 10:00 11:00 12:00 13:00 14:00
Time AEDT
SD
PRD
T µm
ol.m
-2.s
-1
Time AEDT
Time AEDT
Figure 5.10c: Diurnal response of PRD on transpiration (T) on 26 February 2002, ± SEM.
Chapter 5: Physiological response to irrigation and pruning treatments 121
Figure 5.10d: Diurnal response of PRD on transpiration efficiency (A/T) on 26 February 2002, ± SEM.
Figure 5.10e: Diurnal response of PRD on intercellular CO2 partial pressure (Ci) on 26 February 2002, ± SEM.
-2.00
-1.80
-1.60
-1.40
-1.20
-1.00
-0.80
-0.60
-0.40
-0.20
0.00
6:00 7:00 8:00 9:00 10:00 11:00 12:00 13:00 14:00
Time AEDT
Ψ
SD
PRD
ψL
MPa
0
1
2
3
4
5
6
7
8
9
10
6:00 7:00 8:00 9:00 10:00 11:00 12:00 13:00 14:00
Time AEDT
µ
SD
PRD
0
50
100
150
200
250
300
350
400
6:00 7:00 8:00 9:00 10:00 11:00 12:00 13:00 14:00
Time AEDT
µ
SD
PRD
Time AEDT
Time AEDT
Time AEDT
A/T
µmol
.mm
ol-1
Ci µ
mol
.mol
-1
Figure 5.10f: Diurnal response of PRD on leaf water potential (ΨL) on 26 February 2002, ± SEM.
Chapter 5: Physiological response to irrigation and pruning treatments 122
-2.00
-1.80
-1.60
-1.40
-1.20
-1.00
-0.80
-0.60
-0.40
-0.20
0.00
6:00 7:00 8:00 9:00 10:00 11:00 12:00 13:00 14:00
Time AEDT
Ψ SD
PRD
ψs
MPa
Time AEDT
Figure 5.10g: Diurnal response of PRD on osmotic potential (ΨS) on 26 February 2002, ± SEM.
Figure 5.10h: Diurnal response of PRD on turgor on 26 February 2002, ± SEM.
0.00
0.20
0.40
0.60
0.80
1.00
1.20
6:00 7:00 8:00 9:00 10:00 11:00 12:00 13:00 14:00
Time AEDT
SD
PRD
Time AEDT
MPa
Diurnal measurements conducted on 14 February 2003
A 13 hour diurnal (dawn to dusk) was conducted on 14 February 2003 to assess the
physiological response of PRD irrigated vines as VPD increased during the day and
decreased during late afternoon. Stomatal conductance (gs) followed a similar trend to VPD
throughout the day. It increased in the morning, stabilised at midday and decreased in the
afternoon (Figure 5.11a). Α and Τ responded to the decrease in gs by PRD (Figures 5.11b
and c). However Α decreased at 16:00 AEDT for SD vines which, may have been due to
photoinhibition as no corresponding decrease in gs was observed. Α/Τ was relatively
improved in the morning by PRD, although no treatment effects were found after 11:00
Chapter 5: Physiological response to irrigation and pruning treatments 123
AEDT (Figure 5.11d). A large difference in Ci was observed at pre-dawn between PRD and
SD vines (Figure 5.11e). Ci stabilised at a concentration of approximately 230 µmol.mol-1.
Pre-dawn ΨL was –0.42 MPa for both treatments and ΨL decreased as VPD increased
(Figure 5.11f). ΨS followed a similar trend and decreased as VPD increased (Figure 5.11g).
In the absence of treatment differences in ΨL and ΨS, cell turgidity was unaffected by the
treatments (Figure 5.11h).
0
50
100
150
200
250
300
350
400
6.00 8.00 10.00 12.00 14.00 16.00 18.00
Time AEDT
SD
PRD
Time AEDT
g s m
mol
.m-2.s
-1
Figure 5.11a: Diurnal response of PRD on stomatal conductance (gs) on 14 February 2003, ± SEM.
0
5
10
15
20
25
6.00 8.00 10.00 12.00 14.00 16.00 18.00
Time AEDT
µ
SD
PRD
A µm
ol.m
-2.s
-1
Time AEDT
Figure 5.11b: Diurnal response of PRD on photosynthesis (A) on 14 February 2003, ± SEM.
Chapter 5: Physiological response to irrigation and pruning treatments 124
Figure 5.11c: Diurnal response of PRD on transpiration (T) on 14 February 2003, ± SEM. Figure 5.11d: Diurnal response of PRD on transpiration efficiency (A/T) on 14 February 2003, ± SEM.
0
50
100
150
200
250
300
350
400
6.00 8.00 10.00 12.00 14.00 16.00 18.00
Time AEDT
µ
SD
PRD
0
2
4
6
8
10
12
6.00 8.00 10.00 12.00 14.00 16.00 18.00
Time AEDT
SD
PRD
0
1
2
3
4
5
6
7
8
9
10
6.00 8.00 10.00 12.00 14.00 16.00 18.00
Time AEDT
µ
SD
PRD
Time AEDT
Time AEDT
Time AEDT
T µm
ol.m
-2.s
-1C
i µm
ol.m
ol-1
A/T
µmol
.mm
ol-1
Figure 5.11e: Diurnal response of PRD on intercellular CO2 partial pressure (Ci) on 14 February 2003, ± SEM.
Chapter 5: Physiological response to irrigation and pruning treatments 125
Figure 5.11f: Diurnal response of PRD on leaf water potential (Ψ ) on 14 February 2003, ± SEM.
L
Figure 5.11g: Diurnal response of PRD on osmotic potential (ΨS) on 14 February 2003, ± SEM
Figure 5.11h: Diurnal response of PRD on turgor on 14 February 2003, ± SEM.
-2.00
-1.80
-1.60
-1.40
-1.20
-1.00
-0.80
-0.60
-0.40
-0.20
0.00
6:00 7:00 8:00 9:00 10:00 11:00 12:00 13:00 14:00 15:00 16:00 17:00 18:00
Time AEDT
Ψ SD
PRD
-2.00
-1.80
-1.60
-1.40
-1.20
-1.00
-0.80
-0.60
-0.40
-0.20
0.00
6.00 8.00 10.00 12.00 14.00 16.00 18.00
Time AEDT
⎝
SD
PRD
0.00
0.20
0.40
0.60
0.80
1.00
1.20
6:00 7:00 8:00 9:00 10:00 11:00 12:00 13:00 14:00 15:00 16:00 17:00 18:00
Time AEDT
SD
PRD
Time AEDT
Time AEDT
Time AEDT
ψs
MPa
M
Pa
ψL
MPa
Chapter 5: Physiological response to irrigation and pruning treatments 126
5.6 DISCUSSION
5.6.1 Irrigation Effect on Leaf Gas Exchange
Partial rootzone drying reduced mean (ca. veraison to harvest) gs, A and T compared to
standard drip irrigation in seasons 2001-02 and 2002-03. The mean gs, A, T rates between
veraison and harvest for both seasons were comparable to previous studies conducted on
Vitis vinifera in semi-arid climates (Winkel and Rambal 1993; Naor and Wample 1994;
Correia et al. 1995). However, actual values were greater in the second season, particularly
for SD. This may be attributed to relatively high soil water content in January 2003 due to a
large rainfall event (58 mm) on 31 December 2002. The absolute reduction in gs by PRD
was 43 and 34 mmol.m-2.s-1 for seasons 2001-02 and 2002-03, respectively. These
reductions are similar to absolute differences reported by Dry (1995) for partial rootzone
drying of field-grown Cabernet Sauvignon vines. The reductions in A and T may be
attributed directly to stomatal limitation, as the decrease trends in gs by PRD relative to SD
in 2001-02 and 2002-03 were similar. There was a curvilinear relationship found between gs
and A (R2 = 0.748, p<0.001). Also, the rates of A and T were greater in season 2002-03
compared to the previous season, which corresponded to increases in gs. The percent
decrease of A relative to T was less for both seasons for PRD compared to SD. As a result,
carbon fixation per unit of water transpired was improved by PRD relative to SD. Improved
A/T of grapevines is important for the sustainability of Australia’s wine-grape industry, as
water is a limited resource because of water restrictions being imposed on the River Murray.
Ci was not influenced by irrigation practice when seasonal results were pooled. This may
suggest that stomatal limitation was not the only factor contributing to the reduction of A by
PRD. Stomatal closure and reduction in mesophyll CO2 availability have been shown to be
the main factors responsible for reductions in A as soil water content decreases (Chaumont
et al. 1997; Correia et al. 1995). However, other studies indicate that non-stomatal
limitations can also reduce A, including photoinhibition (Powles 1984), photoinactivation of
photosystem II (PSII) (Flexas et al. 2001) and inhibition of CO2 metabolism by reduction in
ATP production and ribulose-1,5-bisphosphate (RuBP) regeneration (Maroco et al. 2002).
The summer midday PAR of the Sunraysia region is often > 1800 µmol.m-2.sec-1, therefore
photoinhibition may be expected as grapevines are illuminated with more light than can be
safely dissipated by photo-chemical and non-radiative mechanisms. Given that the summer
Chapter 5: Physiological response to irrigation and pruning treatments 127
conditions of the Sunraysia region would be similar to those reported by Flexas et al. (1999),
photoinactivation of approximately 40-50% of total PSII could be expected during the
course of a 15-hour illumination day (Flexas et al. 2001).
5.6.2 Pruning Effect on Leaf Gas Exchange
5.6.3 Irrigation and Pruning Effect on Leaf Gas Exchange
The influence of pruning treatments on leaf gas exchange was minor compared to the effect
of irrigation method on gs, A and T. MIN increased the rate of gs, A and T in season 2002
relative to SPUR and MECH. The increased photosynthetic capacity of MIN vines may be
associated with the increased crop load in 2001-02 (refer to section 3.3.4). To sustain the
higher yield and produce sufficient photoassimilates to ripen the crop, MIN vines may have
increased the rate of A by increasing gs and internal CO2 metabolism. Wünche et al. (2000)
showed that a positive linear trend existed between whole canopy gas exchange per unit leaf
area and crop load for ‘Braeburn’ apples. However, Poni et al. (1994) found no effect of
crop load on leaf gas exchange of field grown Concord grapevines.
Pruning treatments had no effect on leaf gas exchange in the following season (2002-03).
These results support previous studies, which have shown no statistical differences in
seasonal leaf gas exchange between SPUR and MIN grapevines (Downton and Grant 1992;
Sommer and Clingeleffer 1993; Lakso et al. 1996; Poni et al. 2000; Intrieri et al. 2001).
Downton and Grant (1992) and Poni et al. (2000) found that leaf gas exchange for MIN
vines was higher between budburst and flowering when canopies developed rapidly
compared to SPUR vines, but after flowering, vines of both treatments had similar
photosynthetic rates. Sommer and Clingeleffer (1993) suggested that the higher yield levels
of MIN vines relative to MECH and cane pruned vines were the result of larger canopy size
and therefore, higher net photosynthetic capacity rather than increased photosynthetic
capacity per unit leaf area.
Midday leaf gas exchange was affected by the interaction between irrigation and pruning
treatments, in conjunction with seasonal variation. In season 2001-02, an interesting
integrated response was observed on gs. PRD irrigation significantly decreased the rate of
Chapter 5: Physiological response to irrigation and pruning treatments 128
gs, A and T on SPUR and MECH vines but had no significant effect on MIN vines. This
suggests that SPUR and MECH vines were more sensitive to the water stress induced by the
dry rootzone of PRD and thus decreased the rate of gs to minimise water loss by T. The
increased physiological sensitivity of severely pruned vines, in response to PRD contrasts to
results from previous studies conducted by Lasko et al. (1994), who found no interaction
between crop level and late season water stress on vine physiology (gs, A and ΨL). However,
they did observe a reduction in gs and A by applying a late season water deficit.
Stomatal conductance was not significantly affected by the interaction between irrigation
and pruning in the following season (2002-03). However, a large decrease in photosynthetic
capacity was observed on PRD + MECH vines because of the large reduction in gs relative
to the other PRD treatments. The stomatal limitation by PRD on transpiration was greater
than on photosynthesis, particularly when combined with SPUR vines and as a result,
transpiration efficiency was improved. Again, this may have been in response to the greater
physiological sensitivity of SPUR vines to the decreased water inputs of PRD. Ci was also
reduced by PRD + SPUR, which corresponds to the greater stomatal limitation observed for
this treatment.
The greater stomatal sensitivity of SPUR and MECH vines to PRD relative to MIN vines
may be associated with canopy morphology (Downton and Grant 1992; Sommer et al. 1993;
Intrieri et al. 2001), leaf morphology (Sommer and Clingeleffer 1993; Syvertsen et al. 1995;
Palliotti et al. 2000; Poni et al. 2000) and leaf age (Patakas and Noitsakis 2001). Higher
whole canopy photosynthesis and respiration of MIN compared to SPUR pruned ‘Concord’
grapevines have been attributed to the early spring development of MIN canopies (Lasko et
al. 1996). Also, the ratio of exposed to shaded leaves may be greater on MIN vines due to
restricted growth (Sommer and Clingeleffer 1993), which has positive implications for
whole canopy physiology because sun-lit leaves have greater photosynthetic capacity
(Palliotti et al. 2000). The larger leaves of the SPUR vines may have required a higher plant
water status to maintain cell turgor and consequently gs. Whilst, leaves from MIN vines
may have been better adapted to water-stress, in terms of partitioning carbohydrates between
more sinks, small leaf area, increased leaf thickness and/or reduced susceptibility to
photoinhibition due to a higher relative leaf age (Bertamini et al. 2003). Relative leaf age is
greater on MIN than SPUR vines, as a result of the earlier spring canopy and leaf
Chapter 5: Physiological response to irrigation and pruning treatments 129
development (Intrieri et al. 2001). Patakas and Noitsakis (2001) found mature leaves of
potted Vitis vinifera were less susceptible to water stress than immature leaves, in terms of
the photosynthetic rate. When PRD was applied in late November of each growing season,
the relative age of leaves on SPUR vines was less than those on MIN vines due to delayed
canopy development and therefore possibly more sensitive to reduced water inputs.
However, other studies on field grown vines have shown photosynthetic capacity may
decrease with increased leaf age (Kriedemann 1968; Schultz 1996; Zuffery et al. 2000),
which may suggest leaf morphology may have had a greater influence on stomatal
sensitivity than leaf age in this study.
5.6.4 Leaf Gas Exchange at Different Phenological Stages
Grapevine photosynthetic capacity was assessed at midday between veraison and harvest to
determine the integrated effects of PRD irrigation with the three pruning treatments, SPUR,
MECH and MIN. VPD ranged between 2.5 and 4 kPa. Relative gas exchange results were
not affected by variation in VPD but a large rainfall event (58 mm) occurred at veraison
2003 and increased the subsurface volumetric soil water content. This may have accounted
for the higher rates of gas exchange at 56, 57 and 59 DAF. Subsurface volumetric soil water
content was also increased by the higher irrigation inputs of SD compared to PRD.
Differences in the physiological response and plant water status were expected given the
difference in soil water content between irrigation strategies.
The photosynthetic capacity of the vines, as determined by gas exchange, was greater at
post-veraison than at harvest. The higher rates of gs, A and T may be attributed to leaf
ontogeny, vine phenology or subsurface volumetric soil water content. Poni et al. (2001)
showed a decline in A associated with increased leaf age. However, the effects of leaf
ontogeny on grapevine photosynthesis do not appear to be consistent. Patakas and Noitsakis
(2001) reported higher rates of A for mature leaves under both well-watered and water-
stressed conditions. The phenological stage of berry development may also affect
carbohydrate production by photosynthesis. At veraison and harvest, berries are the
predominant sinks for carbohydrates and increased photosynthesis may be associated with
rapid rates of sugar accumulation. Alternatively, the increased subsurface soil water content
may have increased plant water status and consequently increased gs, A and T. Several
Chapter 5: Physiological response to irrigation and pruning treatments 130
studies have attributed decreased rates of gs, A and T to reduced soil water content and
water-stress (Naor and Wample 1994; Poni et al. 1994; McCarthy 1995).
The application of PRD did not influence gs, A or T at post-veraison when subsurface soil
water content was relatively high as a result of the rainfall event 11 days prior to
measurements. The high soil water content may have increased plant water status of both
SD and PRD irrigated vines and increased photosynthetic activity at a leaf level in response
to greater gs. Subsequent drying of the subsurface soil profile at around 59 days after
flowering caused PRD to have lower gas exchange. The corresponding decrease in A and T
might have been associated with partial stomata closure. The stomatal limitation on T was
greater than on A. As a result, A/T was improved for PRD irrigated vines. PRD continued
to have a large effect on gas exchange until harvest, reducing gs, A and T and increasing
A/T. The decrease in gs, A and T with PRD irrigated vines 95 DAF was associated with an
increase in Ci. This suggests that there was partial closure of stomata and a build-up of
intercellular CO2. Water-stress may have affected measurements just prior to harvest, as all
gas exchange parameters were reduced by PRD, resulting in a reduction in photosynthetic
activity.
The effects of pruning practice on leaf gas exchange between post-veraison and harvest were
inconsistent. MIN increased the rate of A and subsequently transpiration efficiency on days
56 and 95 after flowering with no associated changes in gs, T or Ci. This suggests that there
was an increase in photosynthetic activity (i.e. increased CO2 metabolism). Similarly, SPUR
increased A and A/T at 59 DAF, probably as a result of increased photosynthetic activity.
These results indicate that pruning has an influence on the carboxylation efficiency of the
leaf as opposed to the stomatal effects observed by the imposition of PRD. Carboxylation
efficiency may have been increased by greater mesophyll CO2 availability due to different
leaf anatomy, increased CO2 metabolism and resistance or tolerance to photoinhibition
(Powles 1984; Maroco et al. 2002).
The effects of the interaction between irrigation and pruning on leaf gas exchange were
influenced by the stomatal limitations of PRD and carboxylation efficiency of the three
pruning treatments from veraison through to harvest. As a result of the variation in pruning
treatment effects on measurement days, no integrated trends were apparent. Stomatal
Chapter 5: Physiological response to irrigation and pruning treatments 131
conductance was significantly affected (P<0.05) by the irrigation and pruning interaction on
57, 91, 95 DAF. PRD reduced gs, relative to SD irrigated treatments, and the pruning
treatment effects on gs correspond to those explained in the previous paragraph. The
reduction of gs by PRD may have been triggered by an ABA response to decreasing soil
water content in the dry half of the rootzone (Loveys 1984). The rates of A and T were not
directly associated with gs, probably as a consequence of the difference in carboxylation
efficiency of the pruning treatments.
5.6.5 Irrigation and Pruning Effects on Carbon Isotope Discrimination
MIN reduced ∆ in seasons 2001-02 and 2002-03. Hence, this treatment reduced the
photosynthetic capacity of the vines at a leaf level. This may be attributed to greater
partitioning of photoassimilates between a greater number of leaves, differences in leaf
morphology and/or leaf ontogeny. Downton and Grant (1992) observed that MIN vines had
greater photosynthetic rates than SPUR vines between budburst and flowering when
canopies develop rapidly due to retention of high bud numbers at winter pruning. However,
after flowering there were no differences in photosynthetic rates and at harvest, SPUR
pruned vines had greater photosynthetic capacity at the leaf level. This reduction in
photosynthetic capacity by MIN vines as the season progressed may explain the reduction in
∆ observed in this study.
Carbon isotope discrimination (∆) has been used as an indirect measure of plant
photosynthetic capacity on a range of crops in response to the ratio between intercellular
CO2 and atmospheric CO2 partial pressures (Farquhar et al. 1982, 1989). PRD reduced ∆ in
the three experimental seasons by 2-3%, which suggests a minor decrease in CO2 fixation
due to either increased stomatal limitation or decreased carboxylation efficiency of PRD
irrigated vines. However reduced ∆ is associated with improved water use efficiency in
grapevines, as a result of greater stomatal limitation on T than on A (Gibberd et al. 2002).
Therefore, PRD improved the water use efficiency of Shiraz grapevines in the Sunraysia
region, as determined by both ∆ and leaf gas exchange.
Chapter 5: Physiological response to irrigation and pruning treatments 132
The reduction in ∆ by PRD dominated the interaction between irrigation and pruning in
seasons 2000-01 and 2001-02. However, SPUR and MECH vines were more sensitive than
MIN to PRD in 2002-03. As a result, greater reductions in ∆ and leaf gas exchange were
found for SPUR and MECH when irrigated by PRD. No relationships were found between
yield and ∆ when treatment means were pooled. This suggests that carbon isotope
discrimination may have been lowered by increasing photosynthetic capacity whilst
maintaining stomatal conductance on treatments with higher crop loads, as has been shown
in peanuts (Nageswara Rao and Wright 1994). Alternatively, the reduction of yield
associated with PRD would have produced a positive relationship between yield and ∆,
whereas the high yields produced in conjunction with MIN may have resulted in a negative
relationship between yield and ∆. As a consequence, when integrated treatment yields were
pooled and plotted against ∆, the two opposing relationships may have cancelled each other
out.
5.6.6 Diurnal response of PRD vines to increasing vapour pressure deficit
VPD is determined by temperature and relative humidity and given the low variation in
humidity during summer in the Sunraysia region (see section 2.3); VPD was dominated by
diurnal increases in temperature. Stomata opened early in the morning as PAR approached
1200 µmol.s-1.m-2 as shown by a rapid increase in gs and A. The rate of gs and A stabilised
mid morning (approximately 11:00 AEDT) as VPD reached its maximum and then slowly
declined as VPD decreased in the late afternoon (17:00 AEDT). Similarly, T was reduced in
conjunction with VPD, gs and A in the late afternoon. However, the diurnal increase of T to
the maximum rate was more gradual than the increase of gs or A. An initial decrease in Ci
was associated with the opening of stomatal aperture and loss of CO2 stored in the
mesophyll tissue to atmosphere. Levels of Ci then stabilised for SD and PRD irrigation
treatments between 200-250 µmol.mol-1. Leaf water potential is accepted as an indicator of
plant water status (Kramer 1983) and has been used extensively in viticultural research
(Smart and Coombe 1983). A maximum ΨL was observed at pre-dawn as it approached
equilibrium with soil water potential, then decreased rapidly to a minimum after midday
followed by a gradual recovery during the late afternoon. The diurnal fluctuation of ΨL in
response to VPD agrees with previous diurnal studies conducted on grapevines (Smart and
Coombe 1983; van Zyl 1987; Dry 1997). Interestingly, whilst diurnal leaf water potential
Chapter 5: Physiological response to irrigation and pruning treatments 133
decreased to very low levels as VPD increased (-1.8 MPa on the 24/1/02), assimilation rates
remained relatively high (>15 µmol.m-2.s-1). Schultz (2003) has shown significant reductions
in gas exchange as leaf water potential decreases for cv. Shiraz of mesic origin. However,
grapevine physiological experimentation conducted on V. vinifera cv. Cabernet sauvignon
also at the Deakin Estate vineyard has produced comparable leaf water potentials and
assimilation rates under similar VPD conditions (N. Cooley, pers. comm.). The high
photosynthetic capacity of the experimental grapevines, which are of a more xeric origin
may be associated with the high levels of PAR and sunlight hours of the experimental site
with combined with irrigation. The Shiraz grapevines of this study also have large canopies
relative to grapevines of mesic or hydric origins, thus net photosynthetic capacity is
expected to be greater.
Diurnally, PRD reduced gs compared to SD irrigation, particularly as VPD increased. As a
result, PRD applied a stomatal limitation by partial stomata closure on A and T during the
day. The relationship between gs and A was established in section 5.3.1 and agrees with
previous work conducted on field-grown grapevines under a range of climatic conditions
(Jacobs et al. 1996). These results suggest that the reduction in A and T may be influenced
by partial stomatal closure. However, a recent study by de Souza et al. (2003) has also
highlighted the importance of decreased carboxylation efficiency (electron transport rate and
triose-phosphate utilization) to leaf gas exchange reduction by PRD when compared to full
irrigation. In addition to the reduction in gs of PRD irrigated vines in this study, PRD
maintained ΨL and ΨS compared to SD irrigated vines. The lack of difference in ΨL
between PRD and SD and the absence of osmotic adjustment by PRD irrigated vines may be
attributed to irrigation of the wet half of the rootzone.
Given that PRD applied only 50% of the amount of irrigation water compared to SD over
the season, yet plant water status was maintained, suggests vines were not displaying a
physiological stress response. This differentiates PRD from deficit irrigation practices, such
as reduced deficit irrigation (RDI) because the latter typically results in stomatal limitation
as well as reduced plant water status (de Souza et al. 2003; McCarthy 1997a). Since plant
water status was not altered by PRD, no yield loss should be expected. However, an average
18% decrease in yield, as a result of reduced berry size associated with PRD was observed
over the three seasons in the warm region of Sunraysia (section 3.3.3). The reduced
Chapter 5: Physiological response to irrigation and pruning treatments 134
irrigation inputs of PRD compared to SD may have imposed a water stress during the critical
stages of berry development, when ΨL was not measured. The effects of post-flowering
water stress on berry size is well established (Goodwin and Jerie 1992; Poni et al. 1993;
McCarthy 1997a). However, PRD successfully maintained hydraulic water status throughout
the remainder of the growing season and no significant differences in soil moisture content
between irrigation treatments during berry development were observed. This suggests that
an alternative mechanism for berry reduction by PRD may have occurred pre-veraison. PRD
may have induced a pre-veraison hormonal and/or chemical response early berry
development, possibly ABA. The induced hormonal/chemical synthesis may have reduced
pericarp volume and restricted berry expansion by limiting flexibility and enlargement of
pericarp cells, as previously shown by Ojeda et al. (1999, 2001).
5.6.7 Proposed mechanisms for Stomatal Closure by PRD
The closure of stomata under water deficit conditions is controlled by hydraulic and/or non-
hydraulic (chemical signalling) mechanisms. Hydraulic signalling occurs by changes in
xylem sap tension to reduce plant water status and stomatal conductance in response to soil
water deficits (Dodd et al. 1996). However, if plant water status is maintained and stomatal
conductance is lowered by partial closure of stomata, then it is likely that synthesis of
inhibitory chemical signals activates the movement of solutes out of guard cells and the
subsequent loss of turgor to close stomata. The partial stomatal closure associated with PRD
irrigation coincides with drying of the soil around part of the root system and maintenance
of leaf water potential (Dry and Loveys 1999; Lovisolo et al. 2002; Stoll et al. 2000). This
suggests drying roots produce a “positive” signal, such as abscisic acid (ABA), which
increases in concentration in the xylem sap as the soil dries. Root tips can detect small
changes in soil water content and generate ABA, which acts as a growth inhibitor and stress
indicator (Zhang and Davis 1991). Accumulation of ABA in the leaves has the capacity to
trigger the exodus of potassium ions (K+) and osmotic loss of water from the guard cells.
The guard cells than become flaccid and reduce the stomatal aperture, subsequently
restricting stomatal conductance and water loss through transpiration. Dry (1997) showed
that a reduction in gs in response to partial drying of the root system of grapevines was
associated with an increase in the concentration of ABA in xylem sap.
Chapter 5: Physiological response to irrigation and pruning treatments 135
5.6.8 Single Leaf Gas Exchange Measurements
The determination of the photosynthetic capacity of a vine can be conducted on a leaf or
whole vine scale. Single-leaf photosynthetic response does not always reflect the response
of the whole canopy, as leaf responses vary with age, position and orientation. Intrieri et al.
(1997) found that whole canopy net A was one third that of an individual leaf under
saturating light intensity. Hence, single-leaf A measurements are not indicative of whole
canopy responses and calculations of vine A on a leaf area basis should consider the
phenology of the vine because carbon assimilation varies throughout the growing season
(Howell 2001). However, assessments of single-leaf A have been used extensively for
comparative studies of relative treatment values (Naor and Wample 1994; Poni et al. 1994;
Gomez-del-Campo et al. 2002); because the determination of whole-vine canopy responses
using canopy chambers can be very difficult.
5.7 CONCLUSIONS
a)
b)
PRD irrigation reduced leaf gas exchange (gs, A and T) by partial closure of stomata but
maintained plant water status as determined by ΨL. Transpiration efficiency was
improved by PRD because the stomatal limitation on T was greater than on A.
PRD reduced ∆ in the three experimental seasons by 2-3%, which suggests a small
decrease in CO2 fixation due to increased stomatal limitation. Reduced ∆ is associated
with improved WUE in grapevines (Gibberd et al. 2002). Therefore, PRD improved the
WUE of cv. Shiraz grapevines in the Sunraysia region, as determined by both ∆ and leaf
gas exchange.
c) The level of pruning had minimal effect on grapevine leaf physiology, which supports
previous studies conducted by Sommer and Clingeleffer (1993). Minor gas exchange
effects showed that pruning level influenced carboxylation efficiency and not stomatal
limitations, as photosynthesis was not directly correlated to stomatal conductance.
Chapter 5: Physiological response to irrigation and pruning treatments 136
d) MIN reduced ∆ in two seasons, which indicates a reduction in the photosynthetic
capacity of the vines. This may be attributed to greater partitioning of photoassimilates
between greater numbers of leaves.
e) The effects of the interaction between irrigation and pruning on leaf gas exchange from
veraison through to harvest were influenced by the stomatal limitations of PRD and
carboxylation efficiency of the three pruning treatments.
f)
g) Diurnally, PRD reduced gs, A and T and maintained hydraulic water status compared to
SD irrigation as VPD increased. The lack of difference in ΨL between PRD and SD and
absence of osmotic adjustment by PRD irrigated vines may be attributed to irrigation of
the wet half of the rootzone.
h)
Midday leaf gas exchange was affected by the interaction between irrigation and
pruning treatments in season 2001-02. PRD irrigation significantly decreased the rate of
gs, A and T on SPUR and MECH vines but had no significant effect on MIN vines.
The hypothesis that states “the physiological response of cv. Shiraz will be negatively
affected by the interaction between PRD and light pruning levels, as it nears the critical
‘source:sink’ relationship” was rejected, since SPUR and MECH vines were more
sensitive to PRD than MIN, in terms of relative reductions in gs, A and T. The
sensitivity of severe pruning levels with PRD illustrates the importance of holistic
viticultural evaluation.
Chapter 6: Botrytis bunch rot development and bunch architecture 137
6 BOTRYTIS BUNCH ROT DEVELOPMENT AND BUNCH ARCHITECTURE
6.1 INTRODUCTION AND EXPERIMENTAL AIMS
Botrytis cinerea is an important pathogen of winegrapes that may lead to Botrytis bunch rot.
B. cinerea can be saprophytic using nutrients from dead or dying plant tissue (Agrios 1997).
Latent infection by B. cinerea on grapevines can occur in the receptacle area or cap scar at
anthesis up to four months before visible expression of the disease (McClellan and Hewitt
1973; Kellar et al. 200;). Colonisation of loose floral debris within bunches by B. cinerea
has also been reported (Bulit and Lafon 1977 cited in Savage and Sall 1984). Spore
germination and infection of berries after veraison by B. cinerea can occur during wet
periods, ie. rain events or dew. All infection modes are influenced by bunch and canopy
microclimate. Botrytis bunch rot can cause substantial yield losses in all wine grape
varieties by rotting flower clusters or immature berries or by rotting and desiccation of
mature berries (Emmett and Nair 1991). Furthermore, B. cinerea can negatively influence
berry composition, vinification of musts, protein stability of wine and increase oxidative
breakdown of red wines by laccase activity (Somers 1984).
B. cinerea can be controlled in the vineyard by fungicide application, sanitation and canopy
management. Sources of B. cinerea inoculum within the vines can be reduced by sanitation
practices, such as removing dead canes and mummified bunches at winter pruning.
Mechanisation of harvest and pruning can increase the amount of dead plant material in the
vine, which can lead to increased inoculum loads in the vine (Emmett and Nair 1991).
Canopy management practices, including pruning level, trellising, bunch thinning and leaf
removal may alter canopy microclimate. Increased aeration and reduced humidity in the
fruiting zone may reduce the development of Botrytis and other diseases, such as powdery
mildew (Carroll and Wilcox 2003). Savage and Sall (1983, 1984) reported that mid-season
hedging and wire trellising of Chenin Blanc grapevines resulted in a moderate reduction of
Botrytis bunch rot incidence and severity. Light pruning practices, such as minimal pruning
have been associated with lower incidence and severity of Botrytis bunch rot in Chardonnay
(Emmett et al. 1995). Post-fruit set bunch thinning reduced Botrytis bunch rot on Seyval
Blanc grapevines (Smithyman et al. 1991). Gubler et al. (1987) reported Botrytis bunch rot
of grapevines can be controlled by removal of leaves from nodes adjacent to the bunch. It
Chapter 6: Botrytis bunch rot development and bunch architecture 138
has been hypothesised that the reduction in Botrytis bunch rot by canopy management is
linked to differences in canopy microclimate, characterised by temperature, atmospheric
humidity, wind speed and leaf wetness. However, there is only circumstantial evidence in
the literature to support this hypothesis (Savage and Sall 1984; English et al. 1989).
Bunch architecture also influences the susceptibility of bunches to Botrytis bunch rot.
Cultivars most susceptible to Botrytis bunch rot have compact bunch architecture (Chenin
Blanc, Zinfandel, Riesling and Sauvignon Blanc) (Savage and Sall 1984). The relationship
between tight, compact bunches and increased Botrytis bunch rot may be attributed to the
presence of free water on the berries. Free water is required for the germination of spores of
B. cinerea (Jarvis 1980). Compact bunches exposed to rain or heavy dew may take longer
to dry than loose bunches because of restricted air movement between berries and/or large,
fully hydrated berries in compact bunches may also be more likely to rupture (Sall et al.
1982). The exocarp of a grape berry is its main defence against B. cinerea infection; the
cuticle membrane and epicuticular wax provide a physical barrier against invasion by the
pathogen. A study by Marois et al. (1985) showed that epicuticular wax played an
important role in the resistance of grape berries to infection by B. cinerea. Epicuticular wax
influences pesticide/fungicide retention, water retention, adhesive ability of plant pathogens
(Baker 1982). Cultivars susceptible to B. cinerea infection have reduced cuticle and
epicuticular wax accumulation (Rosenquist and Morrison 1989). Exposed, loose bunches
have greater wax production associated with high light intensities and temperatures and low
relative humidity (Marois et al. 1986; Percival et al. 1993). Thus, these bunches retain less
water on their surfaces and dry faster (Vail and Marois 1991). Increased Botrytis infection
in compact bunches may also be due to the alteration of the epicuticular wax, from well-
defined platelets to an amorphous structure with shallow depressions, by berry contact
within a grape bunch (Marois et al. 1986).
Integrated viticultural practices that manipulate bunch architecture and canopy microclimate
have the potential to minimise Botrytis bunch rot development. The objective of this
experiment was to determine the optimum integrated viticultural practice for cv. Shiraz that
will reduce Botrytis bunch rot development in the field.
Chapter 6: Botrytis bunch rot development and bunch architecture 139
The aims of this study were to:
1) Evaluate the effects of inoculum spore concentration on Botrytis disease development in
bunches.
The integration of lighter pruning with PRD will reduce the level of bunch infection and
disease expression of B. cinerea, as a result of improved canopy microclimate (i.e. reduced
shoot vigour and leaf area) and bunch architecture (i.e. small, loose, exposed bunches).
2) Determine the susceptibility of bunches to B. cinerea infection at flowering, fruit-set,
veraison and pre-harvest.
3) Assess the influence of integrated pruning and irrigation treatments on Botrytis disease
expression at critical stages of bunch development (flowering, fruit-set, veraison and
harvest)
4) Examine the effects of pruning and irrigation treatments on bunch architecture and the
relationship between bunch architecture and Botrytis disease expression.
The following hypothesis was tested in this study:
6.2 METHODOLOGY
6.2.1 Isolates of Botrytis cinerea
Isolates of Botrytis cinerea were collected from randomly selected mummified bunches on
vines at the experimental site (Deakin Estate, Iraak, Victoria). Single spore isolations were
conducted on potato dextrose agar (PDA) and incubated for 24 hours at 25°C. Single
germinating spores were transferred onto PDA plates and the cultures were grown in
constant temperature (25°C) until sporulation occurred (5-7 days). A collection of isolates
was maintained on PDA slopes for sub-culturing for all inoculation experiments. PDA
slopes prepared in sterile screw cap glass vials (McCartney bottles) were inoculated with
pure B. cinerea isolates and allowed to grow. The colony and PDA slope was completely
covered with sterile distilled water to stop the agar from drying out and stored at 4°C.
Chapter 6: Botrytis bunch rot development and bunch architecture 140
Sub-cultures from the isolate collection were prepared on PDA plates at 25°C, 10 days prior
to field inoculations to produce spores for inoculum. Spore suspensions were prepared by
washing sub-cultures with 20 mL of sterile distilled water and transferring the wash solution
to a flask containing 200 mL sterile distilled water. Spores were dispersed in solution by
gently shaking for 60 seconds. The concentration of each spore suspension was determined
in 0.1 mm3 on 10 repeat sub-samples using an Improved Neubauer haemocytometer
(Blaubrand®, Wertheim, Germany) and adjusted to a final concentration of 104 spores.mL-1.
The viability of the spore suspensions was assessed by pipetting 50 µL of each spore
solution onto five Petri dishes containing PDA. The Petri dishes were sealed for 36 hours at
25°C and the mean percentage of germinating spores determined by light microscopy.
6.2.2 Effects of Spore Concentration
The effect of inoculum spore concentration on Botrytis bunch rot incidence and severity was
assessed in seasons 2001-02 and 2002-03. Twelve bunches were randomly selected and
tagged on two vines from SD or PRD irrigation treatments combined with three pruning
treatments (SPUR, MECH or MIN) (n = 144). Bunches at 80% capfall on the vine were
sprayed with spore suspensions of B. cinerea of 3 concentrations: 0, 102 or 104 spores.mL-1.
The bunches were enclosed in polyethylene bags containing 2 mL distilled water to create a
humid environment for 12 hours to encourage Botrytis disease development. Bunches were
left in situ to develop on the vines under ambient conditions.
At harvest (119 days after flowering commenced, DAF) inoculated bunches were picked and
surface-sterilized (SS) to evaluate latent infection or non-surface sterilized (NS) to assess
both surface and latent infection. Surface-sterilized bunches were immersed in 1% sodium
hypochlorite solution for 2 minutes, rinsed once with tap water, rinsed 3 times with distilled
water and air-dried on paper towel for 1 hour. All bunches (SS and NS) were stored in clean
zip-lock bags and frozen for 12 hours at –20°C to encourage tissue degradation. The
bunches were incubated for 7 days at 26°C in zip-lock bags containing damp paper towel to
produce a humid environment to promote Botrytis development and sporulation. Botrytis
incidence was assessed as the percentage of bunches with sporulating conidiophores of B.
cinerea and severity was assessed as the number of sites in bunches where there were
diseased tissues with sporulating conidiophores of B. cinerea. As expression of B. cinerea
Chapter 6: Botrytis bunch rot development and bunch architecture 141
was predominantly on berries within a bunch, severity will be referred to as the number of
berries infected per bunch throughout the remainder of this chapter.
6.2.3 Botrytis Field Inoculations at Flowering
Early season inoculations were conducted at 80% capfall (10 DAF) in seasons 2001-02 and
2002-03. Thirty-two bunches were randomly selected and tagged on two vines from SD or
PRD irrigation treatments combined with three pruning treatments (SPUR, MECH or MIN)
(n = 384). Bunches on the vine were wet-inoculated with a B. cinerea spore suspension (104
spores.mL-1) or a control treatment (sterile distilled water). Bunches were enclosed in a
humid environment for 12 hours and then left to develop on the vines in situ under ambient
conditions.
Bunches were assessed for the incidence and severity of Botrytis disease at four stages of
bunch development in both seasons: flowering (17 DAF), fruit-set (28 DAF), veraison (77
DAF) and harvest (119 DAF). At each stage, inoculated bunches were picked and either SS
or NS as described in section 6.2.2. All bunches were frozen for 12 hours at –20°C and
moist incubated for 7 days at 26°C. Incidence and severity of expressed Botrytis bunch rot
were assessed as explained in section 6.2.2.
6.3.4 Late season Botrytis Field Inoculations
Bunches from each combined irrigation and pruning treatment were inoculated with B.
cinerea at flowering, veraison and pre-harvest to determine the susceptibility of bunches to
Botrytis bunch rot throughout the season. Bunches were randomly selected and inoculated
with a B. cinerea spore suspension (104 spores.mL-1) or sprayed with sterile distilled water
as a control treatment at flowering (17 DAF), veraison (77 DAF) or pre-harvest (114 DAF)
and assessed at harvest (119 DAF) in seasons 2001-02 and 2002-03.
In season 2001-02, two randomly selected bunches were tagged on two vines from each
integrated irrigation and pruning treatment and sprayed with the B. cinerea spore suspension
or the control treatment (n= 144). All bunches were picked at harvest, frozen for 12 hours at
Chapter 6: Botrytis bunch rot development and bunch architecture 142
–20°C and moist incubated for 7 days at 26°C. Incidence and severity of Botrytis bunch rot
was assessed as described in section 6.2.2.
In season 2002-03, the experiment was extended to assess the effects of latent and trash
infection, in addition to assessing the susceptibility of bunches to Botrytis bunch rot. Four
randomly selected bunches were tagged on 2 vines for each integrated irrigation and pruning
treatment and sprayed with the B. cinerea spore suspension or control treatment (n= 288).
Bunches were picked at harvest and surface sterilized (SS) or non-surface sterilized (NS) as
described in section 6.2.2. All bunches were frozen and moist incubated as in the previous
season. Incidence and severity of Botrytis bunch rot were assessed as described in section
6.2.2.
6.2.5 Bunch Architecture
The influence of imposed irrigation and pruning treatments on bunch architecture and
subsequent Botrytis bunch rot development was assessed. Attributes of bunch architecture
for integrated irrigation and pruning treatments were measured at harvest in seasons 2001-02
and 2002-03. Bunch architecture was characterized by bunch size (weight, volume, length
and compactness), by berry parameters (weight and average number.bunch-1) and in relation
to yield parameters (bunch number.vine-1 and kg.vine-1). Bunch volume was measured by
displacement of water (cm3) and bunch compactness was calculated as bunch weight divided
by bunch length (g.cm-1).
6.2.6 Statistical Analysis
Botrytis incidence and severity were analysed by an Analysis of Variance (ANOVA) using
GenStat® 6th Edition (Lawes Agricultural Trust, Rothamsted Experimental Station). All
interactions were balanced and analysed by general ANOVA; treatment structure of
irrigation * pruning * spore load * sterilisation and no blocking structure was implemented.
Seasonal variation in bunch architecture was also analysed using ANOVA. The interactions
were balanced and analysed by general ANOVA; treatment structure of irrigation * pruning
* season and no blocking structure was implemented.
Chapter 6: Botrytis bunch rot development and bunch architecture 143
6.3 RESULTS
6.3.1 Effect of Spore Concentration on Incidence and Severity of Botrytis cinerea
The concentration of the spore suspension used to inoculate bunches at flowering did not
influence incidence or severity of Botrytis over all treatments, when bunches were assessed
at harvest in either 2002 or 2003. Botrytis incidence did not differ significantly between
bunches inoculated with 0, 102 or 104 spores.mL-1 (Table 6.1).
2001-02 2002-03
Table 6.1: Incidence and severity of B. cinerea on bunches from all treatments inoculated in the field at flowering in seasons 2001-02 and 2002-03 at spore suspension concentrations of 0, 102 or 104 spores.mL-1. Significant differences calculated by Fisher’s least significant difference (LSD 5% level) and denoted by ***P<0.001, **P<0.01, *P<0.05, ns = non significant.
Spore Suspension Concentration
Severity (Infected berries bunch-1)
Incidence Incidence Severity (% Infected Bunches) (% Infected Bunches) (Infected berries bunch-1)
0 Spores.mL-1 70.8 2.77 58.3 1.25
102 Spores.mL-1 87.5 3.59 50.0 1.10
104 Spores.mL-1 71.5 2.94 1.56 58.3
P value ns ns ns ns
LSD 17.1 1.17 19.1 0.55
6.3.2 Botrytis Field Inoculations at Flowering
The incidence of Botrytis bunch rot was influenced by the stage of bunch development.
Mean incidence was highest on bunches assessed at harvest in seasons 2001-02 and 2002-03
(Figure 6.1). Mean incidence was significantly lower at fruit-set and veraison in 2002 and at
flowering and veraison in 2003. Similarly, mean Botrytis severity was higher at harvest in
both seasons when bunches were fully mature. Mean Botrytis severity in bunches was
lowest at veraison in season 2002 and at flowering in season 2003.
Bunches inoculated with a B. cinerea spore suspension of 104 spores.mL-1 had a general
trend towards higher incidence than control bunches at flowering and fruit-set in both
seasons. However, the increase in B. cinerea incidence on inoculated bunches was only
significant at flowering in 2001-02 (4.8-fold) and fruit-set in 2001-02 (4.5-fold) and fruit-set
in 2002-03 (2.0-fold) (Table 6.2 and 6.3). Levels of Botrytis incidence were very low for
Chapter 6: Botrytis bunch rot development and bunch architecture 144
both inoculated and control bunches at veraison in both seasons and no differences were
found.
Generally, Botrytis severity was also higher on inoculated bunches compared to control
bunches in both experimental seasons at all stages of bunch development. Botrytis severity
was significantly higher on inoculated bunches at flowering (11.9-fold) and fruit-set (7.8-
fold) in 2001-02 and at fruit-set (2.5-fold) and harvest (1.6-fold) in 2002-03 (Table 6.4 and
6.5).
Severity 2003
Phenological Stage
Flowering Fruit-Set Veraison Harvest
Severity (Infected berries bunch)
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5Severity 2002
Phenological Stage
Flowering Fruit-Set Veraison Harvest
Seve
rity
(Infe
cted
Ber
ries
bunc
h-1)
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
a
bab
cb
a a
c
Incidence 2002
Inci
denc
e (%
Infe
cted
bun
ches
)
0
20
40
60
80
100
Incidence 2003
Incidence (% Infected bunches)
0
20
40
60
80
100
b
a
a
c
a
b
a
c
Incidence (% Infected bunches)
Severity (Infected Berries bunch-1)
LSD = 9.34 LSD = 10.6
LSD = 0.54 LSD = 0.29
Figure 6.1: Mean incidence and severity of Botrytis in seasons 2001-02 and 2002-03 at 4 stages of bunch development; flowering, fruit-set, veraison and harvest. Significant differences between treatment means denoted by different letters as calculated by Fisher’s least significant difference (LSD 5% level).
Chapter 6: Botrytis bunch rot development and bunch architecture 145
The mean incidence and severity of expressed latent infection of B. cinerea was assessed on
SS bunches and the mean incidence and severity of expressed latent plus surface infection
was determined on NS bunches. Generally, Botrytis incidence and severity of infection was
higher on NS bunches than SS bunches at flowering, fruit-set and harvest in both seasons
(Tables 6.2 to 6.5). Again, the levels of Botrytis incidence and severity were very low at
veraison and there were no differences between latent and surface infection.
The interaction between irrigation (SD or PRD) and pruning (SPUR, MECH or MIN) had no
effect on the mean Botrytis incidence (Tables 6.2 and 6.3) or severity (Tables 6.3 and 6.4) at
the four stages of bunch development. However, at harvest in season 2001-02 Botrytis
incidence was higher on treatments that produced larger bunches (i.e. SD + SPUR, PRD +
SPUR and SD + MECH) than on treatments that produced smaller, looser bunches (i.e. PRD
+ MECH, SD + MIN and PRD + MIN) (refer to Table 6.11 and Figure 6.6). This trend was
not observed in the following season and will be discussed in section 6.3.5. A significant
interaction between irrigation and pruning treatments was found at veraison 2002-03, since
PRD + MECH had a higher Botrytis incidence than the other imposed treatments.
Table 6.2: The mean incidence of Botrytis in season 2001-02 on inoculated and control bunches, surface sterilised (SS) and non-surface sterilised (NS) bunches from integrated irrigation and pruning treatments at 4 stages of bunch development. Significant differences between treatment means are denoted by different letters as calculated by Fisher’s least significant difference (LSD 5% level) and significance levels are indicated by ***P<0.001, **P<0.01, *P<0.05, ns = not significant.
Botrytis Incidence (% Infected Bunches) in 2001-02 Treatments Flowering Fruit-set Veraison Harvest
0 spores.mL-1 8.3a 4.2a 2.1 70.8
104 spores.mL-1 39.6b 18.8b 2.1 71.5
P value *** * ns ns
NS 43.8b 20.8b 0.0 81.2b
SS 4.2a 2.1a 4.2 61.1a
P value *** ** ns *
SD + SPUR 18.7 6.2 0.0 93.8
PRD + SPUR 31.2 6.2 0.0 87.5
SD + MECH 18.7 12.5 0.0 81.2
PRD + MECH 31.2 6.2 6.2 56.3
SD + MIN 31.2 25.0 6.3 58.3
PRD + MIN 12.5 12.5 0.0 50.0
P value ns ns ns ns
Chapter 6: Botrytis bunch rot development and bunch architecture 146
Table 6.3: The mean incidence of Botrytis in season 2002-03 on inoculated and control bunches, surface sterilised (SS) and non-surface sterilised (NS) bunches from integrated irrigation and pruning treatments at 4 stages of bunch development. Significant differences between treatment means are denoted by different letters as calculated by Fisher’s least significant difference (LSD 5% level) and significance levels are indicated by ***P<0.001, **P<0.01, *P<0.05, ns = not significant.
Botrytis Incidence (% Infected Bunches) in 2002-03 Treatments Flowering Fruit-set Veraison Harvest
0 spores.mL-1 2.1 18.8a 8.3 52.1
104 spores.mL-1 10.4 38.2b 16.7 70.8
P value ns * ns ns
NS 12.5b 34.0 6.3a 56.2
SS 0.0a 22.9 18.8b 66.7
P value * ns * ns
SD + SPUR 12.5 37.5 12.5a 56.2
PRD + SPUR 6.2 25.0 12.5a 56.2
SD + MECH 0.0 20.8 6.2a 62.5
PRD + MECH 6.2 18.7 37.5b 81.2
SD + MIN 0.0 25.0 0.0a 50.0
PRD + MIN 12.5 43.7 6.2a 62.5
P value ns ns ** ns
Table 6.4: The mean severity of Botrytis in season 2001-02 on inoculated and control bunches, surface sterilised (SS) and non-surface sterilised (NS) bunches from integrated irrigation and pruning treatments at 4 stages of bunch development. Significant differences between treatment means are denoted by different letters as calculated by Fisher’s least significant difference (LSD 5% level) and significance levels are indicated by ***P<0.001, **P<0.01, *P<0.05, ns = not significant.
Botrytis Severity (number of infected berries bunch-1) in 2001-02 Fruit-set Veraison Harvest Treatments Flowering
0 spores.mL-1 0.17a 0.04a 0.06 2.77
104 spores.mL-1 2.02b 0.31b 0.04 2.94
P value *** ** ns ns
NS 2.15b 0.33b 0.00 3.73
SS 0.04a 0.02a 0.10 1.99
P value *** ** ns **
SD + SPUR 0.62 0.13 0.00 5.06
PRD + SPUR 1.56 0.13 0.00 4.75
SD + MECH 0.19 0.00 1.00 3.12
PRD + MECH 1.56 0.06 0.19 1.37
SD + MIN 1.19 0.38 0.13 1.52
PRD + MIN 0.63 0.19 0.00 1.31
P value ns ns ns ns
Chapter 6: Botrytis bunch rot development and bunch architecture 147
Table 6.5: The mean severity of Botrytis in season 2002-03 on inoculated and control bunches, surface sterilised (SS) and non-surface sterilised (NS) bunches from integrated irrigation and pruning treatments at 4 stages of bunch development. Significant differences between treatment means are denoted by different letters as calculated by Fisher’s least significant difference (LSD 5% level) and significance levels are indicated by ***P<0.001, **P<0.01, *P<0.05, ns = not significant.
Botrytis Severity (number of infected berries bunch-1) in 2002-03 Treatments Flowering Fruit-set Veraison Harvest
0 spores.mL-1 0.02 0.35a 0.19 0.98a
104 spores.mL-1 0.19 0.89b 0.56 1.54b
P value ns * ns *
NS 0.21b 0.99b 0.17 1.06a
SS 0.00a 0.25a 0.58 1.46b
P value * ** ns *
SD + SPUR 0.19 0.69 0.56 1.25
PRD + SPUR 0.06 0.25 0.31 1.01
SD + MECH 0.00 0.60 0.19 1.19
PRD + MECH 0.19 0.94 1.00 2.06
SD + MIN 0.00 0.63 0.00 0.75
PRD + MIN 0.19 0.63 0.19 1.50
P value ns ns ns ns
The relationship between Botrytis incidence, imposed irrigation and pruning treatments,
stage of bunch development and latent infection was evaluated as a factorial experiment in
seasons 2001-02 and 2002-03. No significant differences were found between parameters in
2002 (Figure 6.2), as trends at each phenological stage were similar and no interactions
occurred. However, incidence was higher on bunches at harvest, particularly on irrigation
and pruning treatments that produced large bunches (i.e. SD + SPUR, PRD + SPUR and SD
+ MECH). Also, incidence was higher on NS bunches at most phenological stages with the
exception of veraison. The interaction between irrigation and pruning treatments only
influenced Botrytis incidence on NS bunches at harvest. The interaction between incidence,
imposed irrigation treatment, phenological stage and latent infection was significant in
2002-03 (Figure 6.3). Incidence of Botrytis was higher in bunches of all irrigation and
pruning treatment combinations at harvest. Generally, incidence was higher on SS bunches
at harvest, which indicated that latent infection was predominant in season 2002-03,
particularly on PRD + MIN treatments. A corresponding high level of latent infection of B.
cinerea on PRD + MIN was observed at fruit-set. Incidence was also high on SS bunches
from PRD + MECH vines at veraison. This may account for the 100% rate of disease
expression in bunches from PRD + MECH vines at harvest.
Chapter 6: Botrytis bunch rot development and bunch architecture 148
Figure 6.3: Incidence of Botrytis in season 2002-03 of surface (SS) and non-surface sterilised (NS) bunches from integrated irrigation and pruning treatments at 4 phenological stages; flowering, fruit-set, veraison and harvest. Significant differences between phenological stage*treatment*sterilisation were calculated by Fisher’s least significant difference (LSD 5% level). Significance levels are represented by ***P<0.001, **P<0.01, *P<0.05, ns = not significant.
SD+spurPRD+spur
SD+mechPRD+mech
SD+minPRD+min
SS NS SS NS SS NS SS NS0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
Incidence %
eatment
Phenological Stage
HarvestVeraisonFruit set
Flowering
Tr Figure 6.2: Incidence of Botrytis in season 2001-02 of surface (SS) and non-surface sterilised (NS) bunches from integrated irrigation and pruning treatments at 4 phenological stages; flowering, fruit-set, veraison and harvest. Significant differences between phenological stage*treatment*sterilisation were calculated by Fisher’s least significant difference (LSD 5% level). Significance levels are represented by ***P<0.001, **P<0.01, *P<0.05, ns = not significant.
nsLSD=32.7
SD+spurPRD+spur
SD+mechPRD+mech
SD+minPRD+min
SS NS SS NS SS NS SS NS0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
Incidence %
reatment
Phenological Stage
HarvestVeraison
Fruit setFlowering
***
LSD=36.8 T
Chapter 6: Botrytis bunch rot development and bunch architecture 149
The factorial interaction between severity, imposed irrigation and pruning treatments,
phenological stage and latent infection was also assessed in seasons 2001-02 and 2002-03.
No significant interactions were observed in 2001-02 (Figure 6.4), as severity was greater on
NS bunches on the majority of treatments at each phenological stage, particularly at harvest.
Bunches from SPUR-pruned vines were most susceptible to B. cinerea infection at harvest.
This may be associated with bunch architecture. The severity of Botrytis was lower in the
following season and the interaction was significant (Figure 6.5). The severity of Botrytis
was high at fruit-set on NS bunches and at harvest on both SS and NS bunches. Again, PRD
+ MECH had the highest level of B. cinerea at fruit-set, veraison and harvest, which reflects
the high percentage of incidence found.
SD+spurPRD+spur
SD+mechPRD+mech
SD+minPRD+min
SS NS SS NS SS NS SS NS0.00
1.00
2.00
3.00
4.00
5.00
6.00
7.00
8.00
9.00
10.00
Severity (Infected berries bunch-1)
atment
Developmental Stage
HarvestVeraisonFruit set
Flowering
ns
LSD=1.90
Phenological Stage
Tre
Figure 6.4: Severity of Botrytis in season 2001-02 of surface (SS) and non-surface sterilised (NS) bunches from integrated irrigation and pruning treatments at 4 phenological stages; flowering, fruit-set, veraison and harvest. Significant differences between phenological stage*treatment*sterilisation were calculated by Fisher’s least significant difference (LSD 5% level). Significance levels are represented by ***P<0.001, **P<0.01, *P<0.05, ns = not significant.
Chapter 6: Botrytis bunch rot development and bunch architecture 150
SD+spurPRD+spur
SD+mechPRD+mech
SD+minPRD+min
SS NS SS NS SS NS SS NS0.00
1.00
2.00
3.00
4.00
5.00
6.00
7.00
8.00
9.00
10.00S
everity (Infected berries bunch-1)
Treatment
Phenological Stage
HarvestVeraison
Fruit setFlowering
***LSD=0.99
Figure 6.5: Severity of Botrytis in season 2002-03 of surface (SS) and non-surface sterilised (NS) bunches from integrated irrigation and pruning treatments at 4 phenological stages; flowering, fruit-set, veraison and harvest. Significant differences between phenological stage*treatment*sterilisation were calculated by Fisher’s least significant difference (LSD 5% level). Significance levels are represented by ***P<0.001, **P<0.01, *P<0.05, ns = not significant.
6.3.3 Late Season Botrytis Field Inoculations
The susceptibility of developing bunches to Botrytis bunch rot was assessed by inoculating
bunches with B. cinerea at flowering, veraison and pre-harvest and leaving them in situ until
fully mature (harvest). Bunches inoculated at flowering and pre-harvest had a higher level
of mean Botrytis incidence than bunches inoculated at veraison in season 2001-02 (Table
6.6). Mean severity of Botrytis was high on bunches inoculated at flowering and veraison
but bunches inoculated late in the season (pre-harvest) had the lowest degree of disease
expression. No differences in mean incidence or severity were found in bunches inoculated
at flowering, veraison or pre-harvest in season 2002-03.
Chapter 6: Botrytis bunch rot development and bunch architecture 151
Table 6.6: The mean incidence and severity of Botrytis in seasons 2001-02 and 2002-03 on bunches inoculated at flowering, veraison and pre-harvest. Significant differences between treatment means are denoted by different letters as calculated by Fisher’s least significant difference (LSD 5% level) and significance levels are indicated by ***P<0.001, **P<0.01, *P<0.05, ns = not significant.
Botrytis Incidence (% Infected bunches) Botrytis Severity (Infected berries bunch-1) Treatments 2001-02 2002-03 2001-02 2002-03
Flowering 81.2b 57.3 3.73b 1.41
Veraison 52.1a 58.3 4.21b 1.04
Pre-harvest 81.2b 61.5 0.94a 1.30
P value *** ns *** ns
The level of natural infection (% incidence of Botrytis in bunches the from control
treatment) accounted for >73% of the infection observed at each phenological stage in both
seasons, except at harvest 2001-02 when natural infection only accounted for 39% of
Botrytis incidence (Table 6.7). At flowering and veraison of season 2002-03, all recorded
Botrytis disease was due to natural infection as no difference was found between control and
inoculated bunches. Bunches inoculated at flowering and veraison in season 2002-03 had a
higher level of latent infection of Botrytis in relation to surface infection. This may be
correlated with the high level of natural infection observed on these bunches.
Table 6.7: The incidence of Botrytis in seasons 2001-02 and 2002-03 on bunches inoculated at flowering, veraison and pre-harvest. Significant differences between treatment means are denoted by different letters as calculated by Fisher’s least significant difference (LSD 5% level) and significance levels are indicated by ***P<0.001, **P<0.01, *P<0.05, ns = not significant.
Botrytis Incidence (% Infected bunches) 2001-02
Botrytis Incidence (% Infected bunches) 2002-03
Treatments Flowering Veraison Harvest Flowering Veraison Harvest
0 spores.mL-1 79.2 70.8a 29.2a 58.3 58.3 52.1
104 spores.mL-1 83.3 91.7b 75.0b 58.3 58.3 70.8
P value ns * ** ns ns ns
NS - - - 41.7a 43.8a 56.2
SS - - - 75.0b 72.9b 66.7
P value *** ** ns
Severity of Botrytis expression was also strongly influenced by natural infection. Botrytis
severity on control bunches was not significantly different to the severity of Botrytis on
inoculated bunches at flowering and veraison in both experimental seasons (Table 6.8).
However, bunches inoculated at pre-harvest were less influenced by natural infection in both
Chapter 6: Botrytis bunch rot development and bunch architecture 152
seasons. The severity of Botrytis was also higher on SS bunches at flowering and veraison.
This suggests that disease development was predominantly associated with latent infection.
Table 6.8: Severity of Botrytis in seasons 2001-02 and 2002-03 on bunches inoculated at flowering, veraison and pre-harvest. Significant differences between treatment means are denoted by different letters as calculated by Fisher’s least significant difference (LSD 5% level) and significance level are indicated by ***P<0.001, **P<0.01, *P<0.05, ns = not significant.
Botrytis Severity (Infected berries bunch-1) 2001-02
Botrytis Severity (Infected berries bunch-1) 2002-03
Treatments Flowering Veraison Harvest Flowering Veraison Harvest
0 spores.mL-1 3.75 3.42 0.54a 1.25 0.98 0.98a
104 spores.mL-1 3.71 5.00 1.33b 1.56 1.10 1.62b
P value ns ns * ns ns *
NS - - - 0.88a 0.60a 1.06
SS - - - 1.94b 1.48b 1.54
P value - - - *** *** ns
The influence of irrigation and pruning treatments on Botrytis disease development was
assessed on bunches inoculated at flowering, veraison and pre-harvest (Table 6.9). Pruning
had a large influence on the incidence and severity of Botrytis in season 2001-02. As a
result, an interaction between irrigation and pruning was observed. Irrigation and pruning
had minor effect on incidence or severity in 2002-03. Bunches produced on vines irrigated
by PRD had greater incidence of Botrytis disease in season 2002-03 but a significant
difference was only recorded on bunches inoculated at veraison. Pruning had a significant
effect on Botrytis incidence at flowering and veraison in season 2001-02. When bunches
were inoculated early in the growing season, bunches from SPUR vines had the highest
incidence of Botrytis (100%) and bunches from MIN vines had lowest incidence. No
pruning effect was found at harvest or at any phenological stage in the subsequent season.
When the effects of irrigation strategy combined with pruning level on Botrytis incidence in
bunches were evaluated, it was apparent that treatments that produced larger bunches with
more berries bunch-1, such as SD + SPUR, PRD + SPUR and SD + MECH, had higher
incidence in 2002. Bunches from the aforementioned treatments had 100% incidence at both
flowering and veraison. However, the trend between incidence and treatments with large,
compact bunches was not replicated in the following season when irrigation and pruning
treatment effects were assessed.
Chapter 6: Botrytis bunch rot development and bunch architecture 153
Table 6.9: The incidence of Botrytis in seasons 2001-02 and 2002-03 on bunches from integrated irrigation and pruning treatments inoculated at flowering, veraison and pre-harvest. Significant differences between treatment means are denoted by different letters as calculated by Fisher’s least significant difference (LSD 5% level) and significance levels are indicated by ***P<0.001, **P<0.01, *P<0.05, ns = not significant.
Botrytis Incidence (% Infected bunches) 2001-02
Botrytis Incidence (% Infected bunches) 2002-03
Treatments Flowering Veraison Harvest Flowering Veraison Harvest
SD 87.5 87.5 45.8 52.1 45.8a 56.2
PRD 75.0 75.0 58.3 64.6 70.8b 66.7
Irrigation ns ns ns ns ** ns
SPUR 100.0b 100.0b 56.3 53.1 62.5 56.3
MECH 81.2ab 75.0a 68.8 65.6 56.2 71.9
MIN 62.5a 68.7a 31.3 56.3 56.2 56.3
Pruning * * ns ns ns ns
SD + SPUR 100.0 100.0b 50.0 50.0 68.8 56.3
PRD + SPUR 100.0 100.0b 62.5 56.2 56.2 56.2
SD + MECH 100.0 100.0b 75.0 68.7 31.2 62.5
PRD + MECH 62.5 50.0a 62.5 62.5 81.2 81.2
SD + MIN 62.5 62.5a 12.5 37.5 37.5 50.0
PRD + MIN 62.5 75.0ab 50.0 75.0 75.0 62.5
P value ns * ns ns ns ns
The effects of irrigation and pruning on Botrytis severity were also evaluated on bunches
inoculated at flowering, veraison and pre-harvest (Table 6.10). PRD irrigation increased
Botrytis severity on bunches inoculated at veraison relative to SD in season 2002-03.
Significant pruning effects were recorded on bunches inoculated at flowering and veraison
in season 2001-02. SPUR vines were more than twice as susceptible to Botrytis than MECH
and MIN vines at flowering and veraison. No significant interactions between irrigation and
pruning treatments were found in either season. Light pruning levels and PRD reduced
botrytis severity at flowering and veraison in the first experimental season but PRD
increased severity at each phenological stage (i.e. flowering, veraison and pre-harvest) in the
following season under all pruning levels.
Chapter 6: Botrytis bunch rot development and bunch architecture 154
Table 6.10: Severity of Botrytis in seasons 2001-02 and 2002-03 on bunches from integrated irrigation and pruning treatments inoculated at flowering, veraison and pre-harvest. Significant differences between treatment means are denoted by different letters as calculated by Fisher’s least significant difference (LSD 5% level) and significance levels are indicated by ***P<0.001, **P<0.01, *P<0.05, ns = not significant.
Botrytis Severity (Infected berries bunch-1) 2001-02
Botrytis Severity (Infected berries bunch-1) 2002-03
Treatments Flowering Veraison Pre-Harvest Flowering Veraison Pre-Harvest
SD 4.46 4.71 0.88 1.17 0.77a 1.06
PRD 3.00 3.71 1.00 1.65 1.31b 1.54
Irrigation ns ns ns ns ns **
SPUR 6.81b 7.06b 1.44 1.38 1.28 1.16
MECH 2.50a 3.00a 0.81 1.44 0.91 1.62
MIN 1.88a 2.56a 0.56 1.41 0.94 1.12
Pruning *** *** ns ns ns ns
SD + SPUR 7.25 7.75 1.62 1.25 1.31 1.25
PRD + SPUR 6.38 6.38 1.25 1.50 1.25 1.06
SD + MECH 4.00 4.00 0.88 1.37 0.31 1.19
PRD + MECH 1.00 2.00 0.75 1.50 1.50 2.06
SD + MIN 2.13 2.38 0.13 0.87 0.69 0.75
PRD + MIN 1.62 2.75 1.00 1.94 1.19 1.50
P value ns ns ns ns ns ns
6.3.4 Seasonal Effects on Bunch Architecture
Bunch architecture was evaluated in seasons 2001-02 and 2002-03, in terms of bunch
number vine-1, bunch weight, berry number bunch-1, berry weight, bunch volume, bunch
length, maximum bunch width and bunch compactness (Table 6.11).
Yield Parameters
Bunch number vine-1 was significantly reduced (58%) in 2003 compared to the previous
season, which may be attributed to poor bunch initiation in November 2001-02 (discussed
further in section 3.3.4). In conjunction with reduced bunch number vine-1 in 2002-03,
mean bunch weight, berry number bunch-1 and berry weight increased in relation to the
previous season by 1.2-fold, 1.1-fold, 1.1-fold, respectively.
Bunch Architectural Characteristics
Bunch length and maximum width decreased in 2002-03 by 29% and 18%, respectively.
(Table 6.11). No significant difference in bunch volume was found between 2001-02 and
2002-03. Since bunch length and width decreased in 2002-03 but bunch weight increased
Chapter 6: Botrytis bunch rot development and bunch architecture 155
and volume was not altered, bunch architecture was altered to produce more compact
bunches. Bunch compactness (calculated as bunch weight divided by length) significantly
increased in 2003 (1.33-fold) compared to 2002.
Table 6.11: Bunch architectural parameters, pooled over all treatments, at harvest in seasons 2001-02 and 2002-03. Significant differences between seasons are denoted by different letters as calculated by Fisher’s least significant difference (LSD 5% level) and significance levels are indicated by ***P<0.001, **P<0.01, *P<0.05, ns = not significant.
Season Treatments 2001-02 2002-03 P value LSD Bunch Number Vine-1 379.0b 159.3a *** 21.69 Mean Bunch Weight (g) 58.7a 71.1b *** 4.25 Berry Number Bunch-1 55.0a 60.6b ** 3.34 Mean Berry Weight (g) 1.01a 1.14b *** 0.03 Bunch Volume (cm3) 61.9 56.6 ns 9.19 Bunch Length (mm) 150.0b 107.0a *** 7.12 Max bunch width (mm) 68.7b 57.1a *** 3.90 Compactness g mm-1 0.51a 0.68b *** 0.04
6.3.5 Integrated irrigation and pruning effects on bunch architecture
The effects of integrated irrigation and pruning on bunch architecture were assessed in
seasons 2001-02 and 2002-03 (Figures 6.6 and 6.7). No significant interactions were found
between irrigation and pruning for bunch weight, volume, length, maximum width or berry
number bunch-1 but a significant interaction was observed for bunch compactness. The lack
of significance can be attributed to the additive effect of irrigation and pruning treatments on
bunch architectural parameters.
Bunch Weight and Berry Number Bunch-1
A reduction in bunch weight was associated with the imposition of PRD compared to SD and
MECH and MIN compared to SPUR (Figure 6.6a). Bunch weight did not differ between
seasons when vines were SD irrigated and SPUR pruned but an increase in weight was
observed for bunches from both MECH and MIN vines when SD irrigated in 2002-03.
Similarly, bunch weight increased on MECH and MIN vines when they were PRD irrigated in
2003 but decreased on SPUR vines irrigated by PRD. A similar trend was observed for berry
number bunch-1. MECH and MIN vines produced bunches with more berries in 2002-03 than
in 2001-02 when vines were irrigated by SD or PRD (Figure 6.6b).
Chapter 6: Botrytis bunch rot development and bunch architecture 156
Bunch Volume, Width and Length
Bunch volume was predominantly affected by pruning treatments. Bunch volume decreased
progressively from SPUR to MECH to MIN vines in both seasons (Figure 6.6c). No seasonal
effects on bunch volume were observed on SD irrigated vines but bunch volume decreased in
2002-03 when vines were irrigated by PRD. Bunch width was reduced in 2002-03 for all
integrated irrigation and pruning treatments (Figure 6.6d) and decreased from SPUR to
MECH to MIN treatments under SD or PRD irrigation treatments. Bunch length was
generally unaffected by irrigation and pruning treatments in 2001-02. However, pruning
treatments influenced bunch length in 2002-03 (Figure 6.6e). Bunches decreased in length for
SPUR relative to MECH to MIN treatments on both SD and PRD irrigated vines.
Bunch Compactness
The interaction between irrigation and pruning treatments over the 2 seasons was significant
for bunch compactness. Compactness (bunch weight/length) was greater in 2002-03 than
2001-02 for all integrated irrigation treatments except SD + MECH (Figure 6.6f). The
combination of PRD irrigation and light pruning levels reduced bunch compactness in both
seasons. Compactness was reduced significantly by PRD relative to SD irrigation in both
seasons. Light pruning levels (MIN) reduced bunch compactness compared to SPUR in
season 2001-02 but no difference was recorded between pruning levels in 2002-03.
SD + SPUR SD + MECH SD + MIN
PRD + MIN PRD + MECHPRD + SPUR
Figure 6.6: Photograph of representative bunch architecture for each of the combined irrigation and pruning treatments in season 2001-02.
Chapter 6: Botrytis bunch rot development and bunch architecture 157
Figure 6.7: Effect of irrigation and pruning treatments at harvest 2001-02 ( ) and 2002-03 ( ) on bunch architectural parameters; a. mean bunch weight, b. berry number vine-1, c. bunch volume, d. maximum width, e. bunch length and f. compactness. Significant differences were calculated by Fisher’s least significant difference (LSD 5% level1) and significance levels are indicated by ***P<0.001, **P<0.01, *P<0.05, ns = not significant.
ars calculated on LSD of treatments for each season. 1 Error b
SD+S
pur
SD+M
ech
SD+M
in
PRD
+Spu
r
PRD
+Mec
h
PRD
+Min
Com
pactness g mm
-1
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
20022003
Maxim
um W
idth mm
0
20
40
60
80
100
SD+S
pur
SD+M
ech
SD+M
in
PRD
+Spu
r
PRD
+Mec
h
PRD
+Min
Bun
ch L
engt
h m
m
0
20
40
60
80
100
120
140
160
180
Bun
ch V
olum
e cm
3
0
20
40
60
80
100
120
Berry Num
ber Bunch
-1
0
20
40
60
80
100
Bun
ch W
eigh
t g
0
20
40
60
80
100
120
***LSD = 0.1
nsSD = 22.5
nsLSD = 9.6
nsLSD = 10.3
nsLSD = 18.4
nsLSD = 17.5
L
a. b.
c. d.
e. f.
2001-02 2002-03
Chapter 6: Botrytis bunch rot development and bunch architecture 158
6.3.5 Bunch architecture and Botrytis cinerea incidence and severity at harvest
A significant linear relationship (R2= 0.87, P<0.01) was found between incidence (%) of B.
cinerea and average bunch weight of the six combined irrigation and pruning treatments at
harvest in season 2002 (Fig 6.8a). Larger, heavier bunches had a greater incidence of
Botrytis than smaller bunches. Similarly a significant linear relationship (R2= 0.94, P<0.01)
(Fig 6.8b) was observed between severity of Botrytis for each of the imposed irrigation and
pruning treatments and average bunch weight for those treatments at harvest in season 2002.
Incidence
Average bunch weight g
20 40 60 80 100 120
Inci
denc
e (%
Infe
cted
bun
ches
)
40
50
60
70
80
90
100
Severity
Average Bunch Weight g
20 40 60 80 100 120
Seve
rity
(Infe
cted
ber
ries
bunc
h-1)
0
1
2
3
4
5
6
R2 = 0.87 R2 = 0.94
b. a.
Figure 6.8 Linear relationships between a. incidence (R2= 0.87, P<0.01) and b. severity (R2= 0.94, P<0.01) of Botrytis and mean bunch weight for integrated irrigation and pruning treatments in 2001-02.
No linear relationship was found between Botrytis incidence or severity and mean bunch
weight of the six combined irrigation and pruning treatments in the following season (Figure
6.9a and b). The lack of relationship is related to a change in bunch architecture and
favourable weather conditions prior to harvest in 2002-3. A large rainfall event (37 mm),
below average maximum summer temperature (23°C) and 100% relative humidity occurred
on the 21 February 2003, which may have induced natural infection of Botrytis, therefore
overriding architectural effects. The levels of mean incidence and severity were lower for
most integrated treatments in 2002-03 compared to 2001-02.
Chapter 6: Botrytis bunch rot development and bunch architecture 159
Incidence
Average bunch weight g
20 40 60 80 100 120
Inci
denc
e %
45
50
55
60
65
70
75
80
85
Severity
Average Bunch Weight g
20 40 60 80 100 120
Poin
ts o
f Inf
ectio
n
0.0
0.5
1.0
1.5
2.0
2.5
R2 =0.014R2 = 0.009
a. b.
Figure 6.9: Linear relationships between a. incidence (R2= 0.014, P<0.01) and b. severity (R2= 0.009, P<0.01) of Botrytis and mean bunch weight for integrated irrigation and pruning treatments in 2002-03.
6.4 DISCUSSION
6.4.1 Influence of Spore Concentration on Inoculation Experiments
Spore concentration of inoculum can influence the development of Botrytis in bunches in
the field. Warren et al. (2000) reported a difference in the incidence of Botrytis rot on
bunches with spore concentrations between 103 and 104 spores.mL-1. However, in the studies
reported here, the incidence and severity of expressed Botrytis at harvest on bunches wet
inoculated at flowering was not influenced by inoculum spore concentrations between 0 and
104 spores.mL-1 of B. cinerea. These results are not consistent with those of the field
inoculation study conducted by Warren et al. (2000).
The lack of difference in Botrytis rot on incubated bunches suggests that either natural
infection of B. cinerea occurred without field expression on bunches from inoculum carried
over from the previous season, the wet application method encouraged Botrytis development
and/or the incubation conditions in the laboratory were highly conducive to Botrytis
development. Studies by Nair et al. (1995) indicated that 70% of variation in flower
infection on field-grown grapevines was associated with carry-over inoculum from the
Chapter 6: Botrytis bunch rot development and bunch architecture 160
previous season and flower infection accounted for 78% of berry infection. In this
experiment, the potential for high levels of carry-over inoculum and berry infection in
season 2002-03 was high because the same vines were used for the experiments for two
seasons. Also, no fungicides were applied to the Shiraz vineyard to control B. cinerea and
dead plant material was present because the surrounding vineyards were mechanically
harvested and pruned. As a consequence, levels of natural inoculum were likely to be high.
Inoculation by the wet application method may have also encouraged B. cinerea infection.
Coertze and Holz (1999) found fresh grape berries, previously considered susceptible to B.
cinerea when applied as wet inoculum, were resistant to infection from dry conidia. The
authors suggested that spore distribution was restricted to the region of the water droplet
from wet inoculation, creating a highly localised zone of disease pressure and the
subsequent collapse of host resistance. Inoculation with dry conidia of B. cinerea using
settling chambers (Coertze and Holz 1999; Cook et al. 2002) has been used effectively in
the laboratory. However, controlled in situ field inoculations were not possible using this
method. Finally, removal of bunches and incubation in conditions with optimal temperature
and humidity in the laboratory was conducive to Botrytis development and sporulation on
infected tissues. The incubation would have promoted the expression of infections arising
from natural and artificially applied inoculum.
6.4.2 Botrytis incidence and severity at different bunch development stages
Bunches were less resistant to secondary infection of Botrytis when fully developed and at
maximum maturity (TSS >22°Brix). Bunches inoculated at flowering and left in ambient
conditions on the vine until harvest had higher incidence and severity of Botrytis compared
to bunches assessed earlier in the growing season. This indicates that latent infection by the
pathogen occurred during the growing season (flowering to harvest) without expression of
the disease. If favourable weather conditions (i.e. cool and wet weather) occurred before
harvest, field expression of Botrytis bunch rot would have been expected.
The development of tighter bunches as berry size increased from veraison to harvest and the
increase in berry sugar content may have also influenced Botrytis development. Emmett et
al. (1995) recorded a lower level of rot caused by B. cinerea on loose bunches. This may be
attributed to increased aeration and less epicuticular wax damage by berry-to-berry contact
Chapter 6: Botrytis bunch rot development and bunch architecture 161
(Marois 1986). This may also be extrapolated to developing bunches that are looser when
berries are small. Botrytis disease expression on bunches was less apparent earlier in the
growing season with low incidence and severity reported at flowering, fruit-set and veraison.
The improved microclimate of developing bunches may have been associated with these
lower levels of Botrytis. Also, compounds present in pea-size green berries, such as the
stilbene stress-metabolite, resveratrol, are believed to inhibit infection by the pathogen.
However, recent work by Keller et al. (2003) showed that stilbenes may have a limited role
in the inhibition of flower and latent infection.
Generally, the level of naturally occurring B. cinerea in the vineyard was high throughout
the two experimental seasons, as no significant differences in Botrytis incidence or severity
were observed between control and inoculated bunches at each phenological stage, with the
exception of flowering in 2001-02 and fruit-set in 2002-03. This may be attributed to high
levels of carry-over inoculum levels from previous seasons, especially in 2002-03, as
discussed in section 6.4.1. The source of B. cinerea in bunches at each phenological stage
was predominantly a combination of latent infection, probably in the receptacle area of
berries (Keller et al. 2003) and surface contamination from spores on the surface of berries
or infected trash (i.e. dead plant tissue, such as senescent flower parts) trapped in the
bunches.
6.4.3 Susceptibility of Bunches to late season Botrytis Inoculations
Seasonal effects influenced the development of Botrytis in bunches inoculated at flowering,
veraison and pre-harvest. In season 2001-02, incidence of Botrytis was higher in
inflorescences and mature bunches, whilst severity was higher on inflorescences and
bunches at veraison. The stage of bunch development had no effect on susceptibility to B.
cinerea in the subsequent season. The seasonal variation in bunch susceptibility may have
been associated with more favourable weather conditions for Botrytis development at the
time of infection in season 2001-02. Lower mean monthly temperature and higher mean
monthly relative humidity were recorded from November 2001 to February 2002 compared
to the same growth period in the following season (refer to section 2.3).
Chapter 6: Botrytis bunch rot development and bunch architecture 162
The high susceptibility of inflorescences may have been due to the high levels of decaying
flower tissue trapped in the bunch and easier penetration by the pathogen into the receptacle
area through the cap scar (Keller et al. 2003). Compact bunch architecture and the resultant
bunch microclimate of mature bunches prior to harvest may have produced favourable
conditions for Botrytis bunch rot. The high susceptibility of bunches to Botrytis infection at
flowering and in the pre-harvest period, highlights the need to monitor for Botrytis
development during these growth stages. Also, the application of fungicides for Botrytis
control at flowering and pre-harvest is important if weather conditions are conducive to
infection.
6.4.4 Influence of Integrated Irrigation and Pruning Treatments on B. cinerea
Light pruning levels produce high numbers of bunches per vine and, consequently, alter
bunch architecture. Similarly, PRD irrigation strategies can reduce shoot vigour and reduce
berry size, as shown in section 3.3.4. Given the difference in bunch and canopy architecture
between severe and light pruning treatments and SD and PRD irrigation strategies, it was
hypothesised that combinations of irrigation and pruning practices would influence bunch
susceptibility to Botrytis infection throughout the growing season and Botrytis disease
expression (cf. p.138).
The combination of irrigation and pruning practices did not influence incidence and severity
of Botrytis when assessed at the four stages of bunch development in season 2001-02.
However, treatments that produced large, compact bunches within the fruiting zone of the
canopy, such as SD + SPUR, PRD + SPUR and SD + MECH increased the incidence and
severity of Botrytis at harvest in season 2001-02. In season 2002-03, PRD + MECH had a
significantly higher incidence at veraison compared to all other integrated treatments. This
result may be attributed to increased maturity of these bunches because of the earlier
veraison date associated with PRD irrigation (refer to section 3.2.2). The severity of
infection was not influenced by irrigation and pruning treatments in season 2002-03, even
though bunches from PRD + MECH vines had high Botrytis incidence at veraison.
The susceptibility of bunches from combined irrigation and pruning treatments to infection
by B. cinerea was assessed during bunch growth. Bunches at veraison from PRD irrigated
Chapter 6: Botrytis bunch rot development and bunch architecture 163
vines were more susceptible to B. cinerea infection. This may be associated with the higher
sugar levels of berries from PRD compared to SD irrigated vines, refer to section 3.3.5.
Inflorescences and small, loose ripening bunches from MIN and MECH vines had a lower
incidence and severity of Botrytis than the larger bunches produced on SPUR vines in
season 2001-02. However, this result was not reproduced in the subsequent season
(discussed further in section 6.4.5). The integrated irrigation and pruning treatments
affected Botrytis incidence in bunches at flowering and veraison in season 2001-02. Large,
compact bunches produced by severe pruning (SPUR) and high input irrigation (SD) had
higher Botrytis incidence than in small, loose bunches produced on light pruning (MIN) and
lower input irrigation (PRD). Interestingly, incidence was lowest on ripening bunches from
PRD + MECH vines in season 2001-02 and was highest on the same treatment in the
following season. This large increase in incidence in the second season may be the
consequence of high levels of inoculum carried over from the previous season.
Alternatively, it may indicate that vines subjected to this treatment were stressed due to
insufficient irrigation input and/or high crop levels and thus more susceptible to infection.
Water-stress of grapevines can lead to dehydration and desiccation of berries as a survival
mechanism. Consequently, the level of trash (dead and decaying plant tissue) within a
bunch increases. It has been reported that bunches with high levels of trash were more
susceptible to Botrytis bunch rot (Emmett et al. 1994). Also, dehydrated berries may be
more prone to berry splitting at harvest when vines are rapidly re-hydrated by either large
irrigation or rainfall events. Sall et al. (1982) showed bunches which contained split berries
were highly susceptible to Botrytis infection.
6.4.5 Effects of Irrigation and Pruning on Bunch Architecture and Botrytis infection
It has been established that grapevine cultivars with tight, compact bunches are more
susceptible to Botrytis infection than cultivars that produce small, loose bunches (Savage
and Sall 1984). Presence of free water (Jarvis 1980), berry splitting (Sall et al. 1982),
cultivar variation in cuticle and epicuticular wax (Rosenquist and Morrison 1989) and
exocarp damage by berry contact (Marois et al. 1986) are several explanations for the
increased susceptibility of large, tight bunches. In view of the aforementioned, the effect of
the architecture of bunches on vines with the imposed irrigation and pruning treatments on
Botrytis development were evaluated. Strong positive linear relationships between mean
bunch weight and Botrytis incidence and severity were found in season 2001-02. Larger and
Chapter 6: Botrytis bunch rot development and bunch architecture 164
more compact bunches, as produced by SD + SPUR and PRD + SPUR, had higher Botrytis
incidence and severity. The higher incidence and severity of Botrytis on large, tight bunches
was likely to have been associated with a more favourable microclimate in these bunches for
Botrytis development, berry damage and differences in berry exocarp, as discussed
previously.
However in the following season, there was no relationship between bunch weight and
Botrytis development. The lack of relationship may be explained by changes in bunch
architecture between the two experimental seasons. Irrigation and pruning treatments
produced bunches of distinct bunch architecture in season 2001-02; severe pruning levels
and SD irrigation produced large, compact bunches with many berries per bunch, whereas
light pruning levels and PRD irrigation produced small, loose bunches with fewer berries
per bunch. However in spring 2001, poor bunch initiation on lightly pruned vines (i.e. MIN
and MECH) caused large changes in most bunch architectural parameters in season 2002-03.
Bunch weight, berry number per bunch and berry weight all increased and bunch length and
maximum width decreased for bunches from MIN and MECH pruned vines in 2002-03
compared to the previous season. As a consequence, bunches from MIN and MECH pruned
vines became more compact because more berries were concentrated on a shorter rachis.
The compactness of bunches from light pruning treatments was further increased when
combined with PRD irrigation in season 2002-03. However, bunch architecture was
unaffected in the two seasons by SPUR pruning because severe pruning levels controlled
crop level and subsequently yield components (i.e. bunch weight, berry weight, berry size
and berry number).
This study has shown that light pruning practices combined with PRD irrigation can alter
bunch architecture and this, in turn, has the potential to reduce infection by B. cinerea.
However, bunch architecture is dependent on crop level (bunch number per vine) and light
pruning treatments are more susceptible to seasonal variation in bunch initiation and fruit
set. Consequently, reproduction of the types of bunch architecture required to discourage
Botrytis infection and development may not be achievable every season because of
unfavourable climatic conditions at critical phenological stages (i.e. bunch initiation,
flowering and fruit set).
Chapter 6: Botrytis bunch rot development and bunch architecture 165
6.5 CONCLUSIONS
f)
a) Bunches were least resistant to infection by Botrytis when fully developed and at
maximum maturity. The development of bunches into tighter clusters as berry size
increased from veraison to harvest and the increase in sugar content may have
encouraged development of Botrytis.
b) Inflorescences and mature bunches were more susceptible to secondary infection by B.
cinerea, possibly because of the high levels of trash trapped in inflorescences at
flowering and the compact architecture of mature bunches just prior to harvest.
c) The potential for natural infection of Botrytis in the Shiraz vineyard was high because
the incidence and severity of Botrytis at harvest was not influenced by inoculum spore
concentrations and incubated bunches had a natural infection rate of more than 73%.
d) The source of expressed Botrytis was generally a combination of surface contamination
and latent infection when bunches were inoculated at flowering.
e) This study showed light pruning combined with PRD irrigation produced small, loose
bunches in season 2001-02. However, in the following season, bunch architecture was
more compact on MIN and MECH vines because vines compensated for reduced crop
level by increased fruit-set and average berry size.
Strong positive correlations between bunch weight and Botrytis incidence (R2 = 0.87)
and Botrytis severity (R2 = 0.94) were found in season 2001-02. However, no
significant correlations were shown in the following season.
g) Given the large seasonal variation in results from inoculation experiments in 2001-02
and 2002-03, the hypothesis that light pruning systems combined with PRD would
reduce the level bunch infection and disease expression of B. cinerea was not accepted.
Chapter 7: General Discussion 166
7 GENERAL DISCUSSION
7.1 INTRODUCTION TO THE EXPERIMENT
Modern viticultural practices have improved winegrape production and the economic and
environmental sustainability of Australia’s wine industry. The widespread practice of
mechanised light pruning systems across Australia has reduced production costs and
increased tonnages, without negative impact on fruit or wine quality. Similarly, drip
irrigation strategies that induce a regulated water deficit or partially dry the rootzone are
currently being adopted by industry and can dramatically improve water-use efficiency in
the vineyard. The aim of this holistic study was to evaluate the potential of industry-
recognised, integrated irrigation and pruning systems to improve production sustainability.
The sustainability of winegrape production was determined by important viticultural
parameters: yield, fruit and wine composition, vine physiology and disease development.
Few other research projects have taken a multi-disciplinary, holistic approach to studying
viticultural practices. This study was established to identify optimal integrated management
strategies for warm region, irrigated vineyards and to test the hypothesis that:
“Partial rootzone drying integrated with light pruning techniques can improve sustainability
of winegrape production in warm, irrigated vineyards.”
The experiment investigated the effects of standard drip (SD) and partial rootzone drying
(PRD) irrigation techniques combined with three conventional pruning practices on grape
production, vine physiology and pathological susceptibility of field-grown cv. Shiraz
grapevines. SD and PRD irrigation application and scheduling was based on conventional
industry practice. Hand spur pruning (SPUR), mechanical hedging (MECH) and minimal
(MIN) pruning practices were superimposed on the irrigation treatments. A large-scale field
trial was conducted in the warm, irrigated region of north-west Victoria at a commercial
vineyard at Deakin Estate, Iraak, VIC. The experiment was bi-factorial using a Latin square
design and each integrated treatment was replicated six times.
Chapter 7: General Discussion 167
Winegrape production was assessed as tonnes of crop produced, yield components, fruit
development, fruit chemical and spectral composition. Wine was produced from each
treatment and assessed as an important determinant of winegrape production. Grapevine
physiological studies involved the assessment of the effects of the imposed treatments on
midday gas exchange. Diurnal gas exchange and leaf water potential measurements were
employed to determine if PRD reduced stomatal conductance and maintained leaf water
potential, as described by Dry (1997). The pathological component of the project involved
field Botrytis inoculation experiments to assess the effects of the imposed treatments and
resultant bunch architecture on Botrytis development.
7.2 IRRIGATION EFFECTS ON THE SUSTAINABILITY OF WINEGRAPE PRODUCTION
Partial drying of the grapevine rootzone had a detrimental effect on yield relative to SD
irrigation practice, as a result of reduced mean berry weight at harvest. The reduction in
berry weight may be attributed to the reduction in irrigation input as PRD applies half the
amount of water by halving the number of emitters on each drip line compared to SD
irrigation. However, plant water status was maintained by irrigating half of the vine, as
determined by leaf water potential. This suggests the reduction in berry weight may have
been the result of a pre-veraison hormonal/chemical response (i.e. ABA) induced by partial
drying of the rootzone. As a result, pericarp volume may have been reduced and berry
expansion restricted by modification of the structural properties of cell components and
limitation of subsequent enlargement of pericarp cells.
Given the large decrease in irrigation input (50%) by PRD compared to the relatively small
yield reduction (18%), a large improvement in water use efficiency was measured. An
improvement in water-use efficiency has important economic and environmental
implications. Annual volumetric irrigation licences in the Riverland, Murray Darling, Swan
Hill and Riverina regions are subject to continual water restriction. By substantially
reducing irrigation amounts, fewer demands are placed on the Murray, Murrumbidgee and
Darling Rivers and the potential for vineyard expansion is increased. Reduction in irrigation
amounts can also have important environmental benefits, including reduced inputs to
ground-water tables, soil waterlogging and soil salinisation.
Chapter 7: General Discussion 168
Irrigation had little influence on basic fruit composition: pH, TA and TSS. However, PRD
did improve fruit anthocyanin concentration slightly relative to SD irrigation, possibly due
to the effects of co-pigmentation. Bravdo et al. (1985), Hepner et al. (1985), Matthews et
al. (1990) and Iland (2000) reported increased berry anthocyanin and phenolic concentration
and/or wine colour in association with reduced irrigation. Interestingly, PRD had a strong
positive effect on the spectral parameters of wine, including wine density, wine hue, total
anthocyanin and phenolic concentration and ionised anthocyanin concentration. The
difference between wine spectral and fruit colour and phenolics concentration may be
attributed to co-pigmentation between anthocyanin and exocarp tannins (i.e. quercetin) in
the wine produced from PRD irrigated vines. The influence of cultural practices, such as
PRD irrigation, on co-pigmentation in fruit and wine requires further investigation.
Midday and diurnal leaf gas exchange were affected by partially drying the rootzone. PRD
lowered the rates of midday stomatal conductance, photosynthesis and transpiration in both
experimental seasons, when compared to SD. The absolute reductions in stomatal
conductance were comparable to decreases observed by Dry (1995) during the partial
rootzone drying of field-grown Cabernet Sauvignon vines. Partial closure of stomata has
been associated with increased synthesis of ABA in the dry roots (Loveys 1984a and b;
Loveys and Düring 1984; Stoll et al. 2000) but determination of ABA production was
beyond the scope of this project. Stomatal limitation on photosynthesis and transpiration
was probable, given the strong positive relationship with stomatal conductance and reduced
carbon isotope discrimination by PRD. Internal CO2 concentration was not influenced by
irrigation practice. This suggests other factors, such as photoinhibition and inhibition of
CO2 metabolism, may have also been associated with the reduction of photosynthesis. The
limitation on the amount of water transpired was greater than on the amount of carbon fixed
by photosynthesis. As a result, transpiration efficiency was improved for PRD irrigated
vines compared to SD irrigated vines. Leaf water potential and osmotic potential were
measured diurnally in conjunction with leaf gas exchange to investigate the response of PRD
irrigated vines to increasing VPD. Diurnally, stomatal conductance was reduced by PRD
compared to SD. However, leaf water potential was maintained and no osmotic adjustment
occurred. This suggests PRD maintained plant water status by irrigation of the wet half of
the rootzone but promoted partial closure of the stomata in response to the dry half of the
rootzone.
Chapter 7: General Discussion 169
Bunch susceptibility to Botrytis during the growing season was largely unaffected by
irrigation treatment. However, bunch architecture was different for SD and PRD irrigated
vines, which had implications for Botrytis bunch rot development after artificial infection.
PRD irrigation produced looser bunches with smaller berries than SD irrigated vines. A
strong positive correlation between bunch size and increased incidence and severity of
Botrytis was found in season 2001-02. The small loose bunches of PRD irrigated vines may
have altered bunch microclimate and reduced berry contact within the bunch, which
consequently reduced infection by B. cinerea.
PRD has many advantages over deficit irrigation strategies that apply a hydraulic water
stress to the grapevine, such as RDI. PRD is generally less limited by climatic conditions
than RDI, as it is applied for the entire season compared to the short period post-flowering
(several weeks). Also, PRD irrigated vines are less susceptible to extreme heat conditions
than RDI vines because plant water status is maintained by irrigating one half of the
rootzone. However, if PRD is to be implemented in a vineyard, additional irrigation
infrastructure is required to alternately water each side of the vine.
7.3 PRUNING EFFECTS ON THE SUSTAINABILITY OF WINEGRAPE PRODUCTION
Yield was strongly influenced by pruning level and the resultant bunch number per vine.
The number of nodes retained on the vine after winter pruning and the degree of bunch
initiation during the previous season determined the number of bunches per vine in the
subsequent growing season. Light pruning levels of MIN vines resulted in 4-fold more
bunches per vine than the severe pruning levels of SPUR vines. Mechanical hedged vines
had an intermediate number of bunches per vine. The high bunch numbers of MIN and
MECH treatments were subject to greater seasonal variation than the highly controlled
SPUR pruning treatment. Yield reflected the trend in bunch number per vine. However,
MIN and MECH vines compensated for greater carbohydrate partitioning between
reproductive sinks by producing smaller bunches with fewer berries per bunch.
Chapter 7: General Discussion 170
Pruning level influenced berry maturation in response to bunch number per vine, since
delayed ripening occurred on lightly pruned treatments. Fruit chemical composition was
influenced by berry size. The dilution of organic acids in the larger, more hydrated berries
produced on SPUR vines affected berry juice pH and titratable acidity. Anthocyanin and
phenolic content on a per berry basis was higher for the larger berries produced on SPUR
vines. However, anthocyanin and phenolic concentration was higher from MIN vines in
season 2001-02. The pruning effects on wine composition reflected fruit composition, as
berry size had a strong association with both fruit and wine quality.
Pruning effects on vine physiology were less pronounced. MIN was associated with an
increase in photosynthetic capacity in season 2001-02. Higher photosynthesis and
transpiration rates may have been linked to greater photo-assimilate demands by higher crop
loads in this season. Pruning treatments had no effect on leaf gas exchange in the
subsequent season when crop loads were more uniform. These results support previous
findings, which have shown no significant differences in seasonal leaf gas exchange
between conventionally spur pruned and minimally pruned grapevines (Downton and Grant
1992; Lakso et al. 1996; Poni et al. 2000; Interi et al. 2001). It has been suggested that
higher photo-assimilate demands of light pruning treatments are met by their larger canopy
size, and therefore, higher net photosynthetic capacity (Sommer and Clingeleffer 1993).
The distinct bunch architecture resulting from the pruning treatments influenced Botrytis
bunch rot development. Large, compact bunches from SPUR vines were more susceptible
to Botrytis incidence and severity at harvest in season 2001-02. Bunches produced on MIN
vines were looser with smaller berries. This bunch architecture allows greater aeration of
the bunch and creates a less favourable microclimate for Botrytis disease development.
Also, bunches from MIN vines were generally more exposed to sunlight. Therefore,
epicuticular wax was expected to be thicker, providing greater protection against pathogen
infection. However, low bunch numbers and high fruitset on MIN and MECH vines in
season 2002-03 led to a significant change in bunch architecture. Bunches from MIN and
MECH vines had reduced rachis length and increased berry numbers per bunch and as a
result, became more compact. As a consequence of the increased compactness of bunches
in season 2002-03, no linear relationship between Botrytis development and bunch weight
was found.
Chapter 7: General Discussion 171
Light pruning techniques increased crop production without any negative effect on fruit or
wine composition. In fact, small berries were strongly correlated with improved wine
colour, density and hue. The photosynthetic capacity of MIN vines was sufficient to ripen
the higher crop level. However, maturation was delayed by up to 13 days. Delayed
maturation and harvest may be detrimental in cooler wine regions of Australia but it may be
overcome by thinning for crop control. The loose architecture of MIN bunches discouraged
the development of Botrytis bunch rot in season 2001-02. However, lighter pruning levels
were more susceptible to seasonal variation in bunch initiation and fruitset. Thus, it is
difficult to consistently reproduce bunch architecture that discourages Botrytis infection and
development.
7.4 INTEGRATED IRRIGATION AND PRUNING EFFECTS ON THE SUSTAINABILITY OF
WINEGRAPE PRODUCTION
The integration of SD or PRD irrigation strategies with different pruning practices had
minor effects on grape yield. The additive effect of PRD irrigation treatments combined
with light pruning treatments resulted in few statistically significant interactions. Berry
weight was the only yield component influenced by the interaction during the three
experimental seasons. Berry weight was reduced when PRD was combined with MIN
pruning, in response to lower irrigation inputs and higher bunch number. However, yield
was not negatively affected by the reduction in berry weight by PRD + MIN because of the
increased bunch number associated with lighter pruning. Large yield reductions were
measured when PRD was combined with SPUR, as a result of low bunch numbers and
reduced berry size. An improvement in WUE was an outcome of the reduced irrigation
inputs of PRD combined with the high crop loads of MIN. A 2-fold increase in WUE was
observed for PRD + MIN vines relative to SD + SPUR vines. This has important
environmental sustainability implications, as discussed previously.
Fruit and wine composition were also largely unaffected by integrated irrigation and pruning
treatments, although large berries produced by SD + SPUR had higher anthocyanin and
phenolic content on a per berry basis. However, the latter was predominantly influenced by
berry weight. Wines produced from PRD + MECH and PRD + SPUR vines were brighter
Chapter 7: General Discussion 172
and redder than their SD irrigated counterparts, as determined by wine hue over the three
seasons. The additive effect of PRD combined with light pruning treatments to improve
wine spectral properties did not result in any significant interactions between irrigation and
pruning treatments. However, wine colour, phenolics and density were generally higher for
PRD and lighter pruning. These results are supported by the strong correlation between
small berries and improved fruit and wine composition.
Vine physiology, as determined by midday leaf gas exchange was influenced by the
interaction between irrigation and pruning systems. An interesting integrated effect on
stomatal conductance and carbon isotope discrimination was observed. SPUR and MECH
vines combined with PRD were subjected to greater stomatal limitation than MIN vines with
PRD. The difference in stomatal sensitivity between SPUR, MECH and MIN vines may be
attributed to stress adaptability. MIN vines appear to have been better adapted to reduced
water inputs by PRD because of greater partitioning of carbohydrates between more sinks,
better suited leaf morphology and/or reduced susceptibility to photoinhibition.
The combination of PRD irrigation and light pruning decreased the incidence and severity of
Botrytis bunch rot at harvest in season 2001-02. This was attributed to the looser bunches
and improved bunch microclimate. However, the integrated treatment effects on Botrytis
disease development were not significant in season 2002-03, when differences in bunch
architecture were less pronounced. Those combinations of treatments that produced small,
loose bunches on the outside of the canopy had the advantage of reducing Botrytis infection
and disease expression, as well as allowing better spray penetration.
In conclusion, the hypothesis that partial drying of the rootzone integrated with light pruning
techniques can improve sustainability of winegrape production, in terms of yield, fruit and
wine quality, physiology and disease development may be accepted. Seasonal variation
influenced results obtained in relation to each aspect that was studied but over the three
experimental seasons PRD + MIN was determined to be the preferred strategy to enhance
winegrape production in warm, irrigated vineyards.
Chapter 7: General Discussion 173
7.5 RECOMMENDATIONS FOR THE AUSTRALIAN WINE INDUSTRY
The results from this study indicate the combination of PRD irrigation and minimal pruning
can maintain yield, improve wine composition and minimise disease development of
Botrytis. Additional infrastructure is required when installing PRD irrigation and it may be
argued that applying a 50% water deficit to the grapevines by standard drip irrigation
practices as opposed to partially drying the rootzone could produce similar results.
However, this study has clearly shown that PRD maintained plant water status whilst
applying stomatal limitation to transpiration and photosynthesis. It is important to sustain
hydraulic water status to avoid negative plant responses associated with water-deficit, such
as leaf desiccation, reduced net photosynthetic capacity and yield reduction.
Any yield losses incurred in response to PRD irrigation in this study were compensated for
by the increase in bunch number associated with MIN vines. Therefore, yield was
maintained at a level equivalent to fully irrigated vines. Vine photosynthetic capacity of
PRD + MIN vines was sufficient to fully mature the higher crop load. The combination of
PRD and minimal pruning produced small berries that were associated with improved wine
quality, improved bunch architecture and lower susceptibility to pathogen infection. The
loose bunch architecture of PRD + MIN vines gave rise to a less favourable microclimate for
disease development, reduced berry damage within the bunch and may increase fungicide
spray penetration.
This study also highlights the importance of fungicide spray applications at flowering and
pre-harvest to control Botrytis disease development. This is particularly important when the
potential for natural infection is high because of high levels of source inoculum in the field
and latent infection. Penetration of spray into vines and within bunches was expected to be
higher on open canopies with loose, exposed bunches, as is the case on minimally pruned
vines.
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drying and the involvement of xylem sap ABA in the regulation of stomatal behaviour of sunflower
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References 193
Zhang, J. and Davies, W. (1990) Changes in the concentration of ABA in xylem sap as a function of
changing water status can account for changes in leaf conductance and growth. Plant Cell Enviro. 13:
277-285.
Zhang, J. and Davies, W. (1991) Antitranspirant activity in xylem sap of maize. J. Exp. Bot. 42: 1125-
1132.
Zuffery, V., Murisier, F. and Schultz, H. (2000) A model analysis of the photosynthetic response of Vitis
vinifera L. cvs Riesling and Chasselas leaves in the field: I. Interaction of age, light and temperature.
Vitis 39(1):19-26.
APPENDIX 194
APPENDIX A
Schematic map of the research site at Deakin Estate, Iraak, Victoria highlighting in yellow the
selected experimental rows and corresponding irrigation treatments.
Location:DEAKIN ESTATE Variety: SHIRAZIrrigation Row No.
272829303132333435363738394041
SD 42434445464748
PRD 495051525354555657585960
PRD 6162
SD 63646566676869707172
PRD 7374
SD 757677787980818283848586
Vine No. 0 10 20 30 40 50 60 1
Scale24 m
N
60
APPENDIX 195
APPENDIX B
Schematic representation of irrigation and pruning experimental design at Deakin Estate, Iraak,
Victoria.
PRD = Partial rootzone drying
SPUR = Spur pruning
MECH = Mechanical hedging
Row Irrigation Panel 1 Panel 2 Panel 3 Panel 4 Panel 5 Panel 642 SD MECH MIN SPUR SPUR MIN MECH63 SD SPUR MECH MIN MECH SPUR MIN75 SD MIN SPUR MECH MIN MECH SPUR
49 PRD SPUR MIN MECH MECH MIN SPUR61 PRD MECH SPUR MIN SPUR MECH MIN73 PRD MIN MECH SPUR MIN SPUR MECH
KeySD = Standard dri[p irrigationPRD = Partial rootzone drying irrigationSPUR = Spur pruningMECH = Mechanical hedgingMIN = Minimal pruning
Note: each panel = 8 vines
Experimental Design
KEY
SD = Standard drip irrigation
MIN = Minimal pruning
NOTE: Each panel consists of 8 vines
APPENDIX 196
APPENDIX C
Standardised procedure and formulae for the determination of anthocyanin and phenolic content and
concentration of winegrapes (adapted from Iland 2001).
1. Record the weight of a 100 berry sample (0.01g accuracy) (A).
2. Macerate the berries to a homogenous mixture and measure approximately 1g of homogenate
into a pre-weighed and record the weight (B).
Calculations:
=A x dilution factor x C x A x 1000
=A280 x dilution factor x C x A x 1 100 B 50
3. Add 10 mL of 50% (v:v) aqueous ethanol (acid adjusted to pH 2) to the homogenate.
4. After 1 hour, centrifuge the supernatant at 3500 rpm for 10 minutes.
5. Record the volume of the supernatant (C) and add 1.0 mL of the supernatant to 10.0 mL of 1M
HCl.
6. Allow the diluted HCl extract to incubate for 3 hours at 25°C.
7. Using a spectrophotometer, read the absorbance of the diluted HCl extract at 520 nm and
280nm, using a 10 mm path-length.
Anthocyanin Content (mg anthocyanins / berry)
=A520 x dilution factor x C x A x 1000 500 100 B 50 Anthocyanin Concentration (mg anthocyanins / g berry weight)
520 500 100 B A Phenolic Content (mg phenolics / berry)
Phenolic Concentration (mg phenolics / g berry weight)
=A280 x dilution factor x C x A x 1 100 B A
APPENDIX 197
APPENDIX D
1.
2.
5. Convert all absorbance readings to absorbance at a 10 mm path-length (A).
Calculations
a.
b.
A520
c. Degree of ionisation of anthocyanins (α) = 100% x A520 - A520(SO2)
d.
e.
= 20(A520 – A520(SO2))
f. Total phenolics (AU) = A280 – 4
Standardised procedure and formulae for the determination of wine anthocyanin and phenolic
content and concentration (adapted from Somers and Evans 2001).
Using a spectrophotometer, record the wine spectrum of 400 – 500 nm using a 5 mm path-
length cell and note absorbancies at 420 and 520 nm.
Add 20 µl sodium metabisulphide (SO2) solution to the above sample, mix thoroughly by
inversion for 1 minute and record the absorbance at 520 nm.
3. Add 20 µl acetaldehyde solution to 2 ml wine and incubate for 45 minutes at 25°C. Measure
absorbance at 520 nm in a 5 mm cell.
4. Add 100 µl wine to 10 ml 1M HCl and incubate for 3-4 hours. Measure absorbancies at 520
nm and 280 nm in a 10 mm cell and correct for the dilution used.
A values represent absorbancies at 420 nm or 520 nm of the wine, HCl supernatant or SO2
supernatant, corrected to 10 mm path-length.
Wine density (AU)= A420 + A520
Wine hue (AU) = A420
A520(HCl) - 5/3 . A520(SO2)
Total anthocyanins (mg.l-1) = 20(A520(HCl) - 5/3.A520(SO2))
Ionised Anthocyanins (mg.l-1) = α x Total anthocyanins
APPENDIX 198
APPENDIX E
Copyright 1998, Lawes Agricultural Trust (Rothamsted Experimental Station)
______________________________________________
VARIATE [nvalues=72] Sample
Identifier Values Missing Levels
Plot 72 0 6
FACTOR [modify=yes;nvalues=72;levels=!(42,49,61,63,73,75)] Row
ANOVA analysis of irrigation and pruning treatment effects on yield vine-1 for seasons 2001-2003.
Genstat 5 Release 4.1 (PC/Windows NT) 14 March 2003 14:45:10
Genstat 5 Fourth Edition - (for Windows)
Genstat 5 Procedure Library Release PL11
______________________________________________
"Data taken from File: F:/HARVEST 2003/HARVEST 03 GENSTAT.XLS"
DELETE [redefine=yes] Sample,Plot,Row,Vine,Treatment,Irrig,Prune,Yield_vine
READ Sample
Identifier Minimum Mean Maximum Values Missing
Sample 1.00 36.50 72.00 72 0
FACTOR [modify=yes;nvalues=72;levels=6] Plot
READ Plot; frepresentation=ordinal
READ Row; frepresentation=ordinal
Identifier Values Missing Levels
Row 72 0 6
VARIATE [nvalues=72] Vine
APPENDIX 199
READ Vine
Identifier Minimum Mean Maximum Values Missing
Vine 3.00 24.61 45.00 72 0
FACTOR [modify=yes;nvalues=72;levels=6] Treatment
Treatment 72 0 6
Identifier Values Missing Levels
READ Treatment; frepresentation=ordinal
Identifier Values Missing Levels
FACTOR [modify=yes;nvalues=72;levels=2] Irrig
READ Irrig; frepresentation=ordinal
Irrig 72 0 2
FACTOR [modify=yes;nvalues=72;levels=3] Prune
READ Prune; frepresentation=ordinal
Identifier Values Missing Levels
Prune 72 0 3
VARIATE [nvalues=72] Yield_vine
READ Yield_vine
Identifier Minimum Mean Maximum Values Missing
Yield_vine 2.83 10.09 23.81 72 0
"General Analysis of Variance."
BLOCK Row*Plot
TREATMENTS Irrig*Prune
COVARIATE "No Covariate"
ANOVA [PRINT=aovtable,information,mean; FACT=32; FPROB=yes; PSE=diff,lsd,means;
LSDLEVEL=5]\Yield_vine
APPENDIX 200
.............................................................................
***** Analysis of variance *****
Plot stratum 5 134.043 26.809 1.52
Row.Plot stratum
Prune 2 14.848 7.424 0.42 0.663
SD 10.66 11.58 10.93
Variate: Yield_vine
Source of variation d.f. s.s. m.s. v.r. F pr.
Row stratum
Irrig 1 67.048 67.048 17.49 0.014
Residual 4 15.337 3.834 0.22
Irrig.Prune 2 18.972 9.486 0.54 0.593
Residual 21 371.492 17.690 2.98
Row.Plot.*Units* stratum
36 214.000 5.944
Total 71 835.741
………………………………………………..
***** Tables of means *****
Variate: Yield_vine
Grand mean 10.09
Irrig SD PRD
11.06 9.13
Prune SPUR MECH MIN
9.54 10.07 10.65
Irrig*Prune SPUR MECH MIN
PRD 8.42 8.57 10.38
APPENDIX 201
*** Standard errors of means ***
Table Irrig Prune Irrig*Prune
rep. 36 24 12
e.s.e. 0.326 0.859 1.044
d.f. 4 21 24.30
*** Standard errors of differences of means ***
Table Irrig Prune Irrig*Prune
rep. 36 24 12
s.e.d. 0.462 1.214 1.476
d.f. 4 21 24.30
*** Least significant differences of means (5% level) ***
Table Irrig Prune Irrig*Prune
rep. 36 24 12
l.s.d. 1.281 2.525 3.044
d.f. 4 21 24.30