Leaf area to fruit mass ratio determines the time of veraison in Sauvignon Blanc and Pinot Noir...

Leaf area to fruit mass ratio determines the time of veraison inSauvignon Blanc and Pinot Noir grapevines

A.K. PARKER1,2*, R.W. HOFMANN2, C. van LEEUWEN3, A.R.G. MCLACHLAN4 and M.C.T. TROUGHT1,2

1 Marlborough Wine Research Centre, The New Zealand Institute for Plant and Food Research Limited,Marlborough, 85 Budge Street, PO Box 845, Blenheim 7240, New Zealand

2 Faculty of Agriculture and Life Sciences, Lincoln University, PO Box 84, Lincoln, Christchurch 7647, New Zealand3 Bordeaux Sciences Agro, ISVV, Ecophysiology and Functional Genomics of Grapevines, UMR 1287, Université de

Bordeaux, Villenave d’Ornon F-33140, France4 The New Zealand Institute for Plant and Food Research Limited, Palmerston North, Private Bag 11600,

Palmerston North 4442, New Zealand* Present address: The New Zealand Institute for Plant and Food Research Limited, Lincoln, Private Bag 4704,

Christchurch Mail Centre, Christchurch 8140, New ZealandCorresponding author: Dr Amber K. Parker, email [email protected]

AbstractBackground and Aims: The extent to which the carbohydrate source–sink ratio influences the time of veraisonof different Vitis vinifera L. cultivars was studied for Sauvignon Blanc and Pinot Noir. The aims were to: (i)determine how changing the leaf area: fruit mass (LA : FM) ratio shortly after fruitset alters the timing of veraison;(ii) establish the relative importance of adjusting the vine yield or the leaf area on the timing of veraison; and (iii)evaluate the relative effect on the timing of veraison, leaf area and yield parameters of the two cultivars at similarLA : FM ratios.Methods and Results: Four cane, vertical shoot positioned trained vines were trimmed shortly after fruitset toretain six or 12 leaves per shoot and thinned by removing 0, 50 or 75% of the bunches. The timing of veraison wasassessed by colour change for Pinot Noir, berry softness for Sauvignon Blanc and the day at which a mean of 8°Brixwas reached for both cultivars. Manipulating leaf area had a greater effect on the date of veraison than crop removal,which had no effect, except when vines were trimmed to six leaves. Sauvignon Blanc was always later than PinotNoir for the time to reach 8°Brix at all LA : FM ratio manipulations.Conclusions: Restricting potential carbohydrate sources post-flowering delayed veraison, while removing crop hadless influence.Significance of the Study: Reduced leaf area can delay the time of veraison, which could counter the earlier timingthat could occur from climate change or warmer than average seasons. Conversely, increased leaf area could enabletarget soluble solids to be achieved in cooler seasons.

Keywords: crop removal, cultivar, leaf area, phenology, veraison

IntroductionUnderstanding the influence of canopy management practicesthat manipulate the leaf area to fruit mass (LA : FM) ratio on thedevelopment cycle of the grapevine is important to ensure thata target berry composition is achieved at harvest for each indi-vidual cultivar. A change to this ratio alters the carbohydratesource–sink partitioning of the vine (Hale and Weaver 1962,Candolfi-Vasconcelos and Koblet 1991, Edson et al. 1993,Candolfi-Vasconcelos et al. 1994, Fournioux 1997). Publishedresearch has generally focused on berry composition at harvestrather than investigating the effect of the LA : FM ratio on thetiming or rates of phenological development (in particular,veraison date) and/or the rate of change for various metabolitesduring the maturation phase (sugars/soluble solids, titratableacidity, flavour and aroma compounds). The relative effect ofchanging the different components of the LA : FM ratio have

provided different and often conflicting results. Kliewer andDokoozlian (2005) suggested 0.8–1.2 m2/kg as an appropriatetarget LA : FM ratio. Practically, this can be achieved by theapplication of different training systems (Peterlunger et al. 2002,Wolf et al. 2003, Vanden Heuvel et al. 2004, Kliewer andDokoozlian 2005), shoot thinning (Reynolds et al. 1994a,b,Naor et al. 2002), leaf removal via summer pruning/trimming(Reynolds and Wardle 1989, Petrie et al. 2000a, Kliewer andDokoozlian 2005, Poni et al. 2009, Stoll et al. 2011), cropremoval (Petrie et al. 2000b, Kliewer and Dokoozlian 2005,Nuzzo and Matthews 2006, Petrie and Clingeleffer 2006) andremoval of leaves in the fruiting zone of the canopy (Kliewer1970, Kliewer and Lider 1970, Hunter and Visser 1990a,Guidoni et al. 2008). The last-mentioned approach has alsobeen used with the objective of improving the microclimatearound the fruiting zone, primarily by increasing aeration and

422 Leaf area to fruit mass ratio and veraison Australian Journal of Grape and Wine Research 20, 422–431, 2014

doi: 10.1111/ajgw.12092© 2014 Australian Society of Viticulture and Oenology Inc

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improving fruit exposure, potentially reducing disease pressure(Hunter and Visser 1990b, Guidoni et al. 2008).

Post-flowering there is potential competition between veg-etative and reproductive growth when resources are limitedand required for both processes; therefore, manipulation ofthe LA : FM ratio can influence the extent of this competition.Removal of leaves has been shown to increase lateral shootproduction (Kliewer and Antcliff 1970, Hunter and Visser1990b, Poni and Giachino 2000) and increase the photosyn-thetic activity per unit leaf area of remaining leaves (Hunterand Visser 1988, 1990b, Candolfi-Vasconcelos and Koblet1991, Petrie et al. 2000c, 2003), and likewise shoot toppingincreased photosynthetic activity (Petrie et al. 2003). Cropremoval has little immediate influence on photosynthetic rateand stomatal conductance (Petrie et al. 2000c), but over time,photosynthetic rate can decline (Edson et al. 1995, Petrie et al.2000c), indicating that sink manipulation may also regulatesource activity.

Temperature has been recognised for a long time as a keydriver of phenological development (Winkler et al. 1974, Huglin1978, Jones and Davis 2000, Parker et al. 2011, Sadras andPetrie 2011a,b, Duchêne et al. 2012). The effect, however, ofother environmental and management factors on the time ofveraison is frequently overlooked. For example, carbohydrateavailability, manipulated either by shoot trimming post-bloom(Poni and Giachino 2000) or leaf removal (Ollat and Gaudillere1998, Petrie et al. 2000a) on potted vines can delay the onset ofmaturity (measured by berry growth or colour change). WhileStoll et al. (2011) reported that the rate of soluble solids accu-mulation in berries decreased with trimming, they did not con-sider whether veraison date (onset of maturation) was altered.In contrast, several studies demonstrated that a similar rate ofsugar accumulation occurs at different LA : FM ratios, evenwhen a different soluble solids concentration was achieved atharvest (Wolf et al. 2003, Nuzzo and Matthews 2006, Petrie andClingeleffer 2006). This indicates that changes observed atharvest must have been a result of a change at the onset ofmaturation. Removal of bunches has provided conflictingresults, from no effect (Keller et al. 2005), where fruit wereremoved from shoots not arising from nodes 1 month post-bloom and at veraison), to an advance in fruit maturity atharvest (as measured by a higher soluble solids concentration)in other studies on post-bloom/post-fruitset fruit removal(Guidoni et al. 2002, Nuzzo and Matthews 2006, Petrie andClingeleffer 2006). It remains unclear from the published litera-ture the extent to which altering the LA : FM ratio is changingthe time of veraison, the rate of soluble solids accumulation ora combination of the two. It appears likely, however, that theresponse will depend on site, season, initial LA : FM ratio andthe timing of the manipulation of the LA : FM ratio. Recentresearch by Sadras and Petrie (2011a,b) using historical dataindicated that earlier fruit maturity associated with an increasedtemperature was best explained by a change of onset of matu-ration rather than by the rate of soluble solids accumulation.They found little influence of changing the LA : FM ratio on thetime of veraison within the dataset used, but this was notexplored experimentally.

The ability to change the onset of veraison and ripening bymanipulating the LA : FM ratio provides an important manage-ment protocol to alter the harvest date of grapes. The objectiveof this research was to assess the extent to which manipulatingthe source–sink relation, by changing the LA : FM ratio post-fruitset, influences the time of veraison for two grapevinecultivars: Sauvignon Blanc and Pinot Noir. Additionally, thequestion whether leaf removal or crop removal had a greater

effect on veraison timing was explored. It was hypothesised thatreducing the LA : FM ratio would delay veraison.

Materials and methods

Experimental siteThe experiment was conducted over two growing seasons ina commercial vineyard in the Wairau Valley, Marlborough, NewZealand (41°32′S, 173°51′E). Two adjacent rows of the Vitisvinifera L. cvs Sauvignon Blanc (clone MS, rootstock Richter110) and Pinot Noir (clone 777, rootstock 101-14MGt) wereused in this trial for 2009/10, and the adjacent rows were usedfor each cultivar in 2010/11. Both cultivars were of similar age,with Sauvignon Blanc planted in 1997 and Pinot Noir in 1998.Rows were orientated +15° from north, in a north to southdirection; vines were planted at 1.8 m within the rows and therow spacing was 3.0 m.

Experimental designIn 2009/10, a two (cultivar) × three (crop removal) × two (mainleaf number per shoot) factorial design, randomised within thecultivar, was used with four blocks (four replicates per treat-ment per cultivar) that were designated by trunk circumferencesize, which was measured by taking as the average of the cir-cumference 10 cm below the head of the vine and 10 cm abovethe graft union. Each replicate corresponded to one vineyardbay consisting of three adjacent vines. The LA : FM ratio treat-ments were adjusted on whole vines in six ways: (i) 12 mainleaves per shoot, 100% crop retained on the vine; (ii) 12 mainleaves per shoot, 50% of the crop removed; (iii) 12 main leavesper shoot and 75% of the crop removed; (iv) six main leaves pershoot and 100% crop retained on the vine; (v) six main leavesper shoot and 50% of the crop removed; and (vi) six mainleaves per shoot and 75% of the crop removed.

In 2010/11, a two (cultivar) × two (crop removal) × two(main leaf number per shoot) block design, randomised withineach cultivar, was used with two blocks (two replicates pertreatment per cultivar in each block) that were designated bytrunk circumference as in the previous season. Treatments i, ii,iv and v of the 2009/10 experiment were repeated in 2010/11 toconfirm trends observed in that season. The design of theexperiments enabled equivalent LA : FM ratios developed byleaf or fruit removal (six leaves and 50% crop with 12 leavesand full crop; six leaves and 75% crop with 12 leaves and 50%crop, respectively) to be compared.

Vine managementAll vines were pruned to four 12-node canes (July 2009 andAugust 2010). Canes were lightly wrapped individually to wireslocated 900 mm and 1100 mm from the soil surface, with twocanes attached to each wire, one in the north and one in thesouth direction. The canopy was trained using vertical shootpositioning, with foliage wires maintaining the canopy approxi-mately 300 mm in width. Where two shoots arose from thesame node, one was removed pre-flowering (10–11 November2009 and 19–24 November 2010). General vineyard man-agement (fungicide spraying, irrigation and under-vine weedcontrol) was undertaken in accordance with SustainableWinegrowing NZ (2013) practice (http://www.nzwine.com/sustainability/sustainable-winegrowing-new-zealand/). Leafand crop removal treatments were applied shortly after fruitset,approximately 3.5 weeks after flowering, corresponding to stage31 on the modified Eichhorn-Lorenz (E-L) developmental scale(Coombe 1995) (Table 1). All the shoots on the vines weretrimmed, leaving 12 or six main leaves. Lateral shoots were

Parker et al. Leaf area to fruit mass ratio and veraison 423

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removed at the time of treatment application and bi-weeklythereafter until harvest to maintain a fixed number of mainleaves on all replicates.

For 50% crop removal, all bunches (apical and basal) wereremoved on alternate shoots along the cane. Similarly, 75%crop removal removed all bunches from three of every fourshoots along the cane. Where no bunches were present on ashoot, this shoot was considered to have been ‘crop thinned’,and subsequent shoots were adjusted for this. The 50 and 75%treatments also had bunches removed from non-count shoots(shoots growing from the head of the vine rather than thecane).

Phenology assessment and berry composition measurementsBudburst, flowering and berry size were monitored by visualscoring of the proportion of change on six vines and at fournodes per vine distributed along the row for each cultivar;budburst was defined as E-L stage 4 (green tip) and floweringas E-L 23 (full bloom, 50% caps off).

Two nodes per upper and lower cane were tagged, and theproportion budburst and flowering (cap fall) at each positionwas assessed through the phenological phases. Where there wasa ‘blind’ bud (nodes or buds on canes where there was no shootdevelopment) or a vestigial shoot in the case of flowering andfruitset assessment (less than three leaves), this was excludedfrom assessment and replaced by the adjacent node position(N + 1) assessment. Where N + 1 was also a ‘blind’ bud or ves-tigial shoot, N – 1 was used.

A random 30-berry sample was collected from each replicateplot weekly from about a soluble solids concentration of 5°Brix.The sample was weighed and where appropriate, used forveraison timing assessment.

Veraison was assessed by three methods:

• The proportion of colour change of Pinot Noir vines onbunches on the four tagged shoots (with two bunches pershoot) was assessed twice per week on each replicate

• The individual berries in the 30-berry Sauvignon Blancsample were scored as hard or soft simply by gently pressingon each berry

• Juice was extracted by hand-crushing berries in polythenebags. The soluble solids concentration was measured on

the coarsely filtered juice with an Atago Pocket PAL-1Refractometer (Atago Co., Ltd, Tokyo, Japan). A thresholdsoluble solids concentration of 8°Brix was used as an alternatemeasure of the mid-point (50%) of veraison, which wasinterpolated/extrapolated from soluble solids accumulationdata; this measurement corresponded to the onset of matu-ration (Parker 2012).

The duration of flowering and veraison was assessed as thenumber of days to go from 10 to 90% of the respective stage(for veraison this was estimated by the first two assessmentmethods).

Leaf area estimation and harvest measuresAll leaves between the trunks of the second and third vines ofeach replicate were removed at harvest. The fresh mass of thewhole leaf sample and that of a 100-leaf subsample were meas-ured. Leaf area of the subsample was measured using a LiCOR3100 leaf area meter (LI-COR Inc., Lincoln, NE, USA). For bothcultivars, the total leaf area defoliated (m2) was then calculatedfrom the correlation between leaf fresh mass and leaf area andadjusted to give a value for leaf area in m2/m row where:

y x= + ( )2574 21290 2009 10 (1)

y x= + ( )1836 25444 2010 11 (2)

where y is leaf area (cm2) and x is the fresh mass of 100leaves (g).

At harvest, all four replicates per treatment were handharvested; fruit mass and bunch number per replicatewere recorded. The average number of berries per bunch wascalculated from the average bunch mass and average berrymass.

Modelling and statistical analysisLogistic (Equation 3) and Gompertz (Equation 4) modelswere fitted using maximum likelihood estimation with anexponential distribution for budburst, flowering and veraisondevelopment:

Table 1. Date and day of the year for budburst and flowering and day of the year for leaf area to fruit mass ratio manipulations for Pinot Noirand Sauvignon Blanc in the 2009/10 and 2010/11 seasons in Marlborough, New Zealand.

Pinot Noir Sauvignon Blanc

2009/10 2010/11 2009/10 2010/11

Date (DOY)

50% budburst 3 October (276) 5 October (278) 14 October (287) 8 October (281)

50% flowering 13 December (347) 4 December (338) 22 December (356) 9 December (343)

Duration (days)

Budburst 24.5 10.8 11.7 9.9

Flowering 8.8 9.7 9.2 8.1

LA : FM ratio manipulations

Date undertaken (DOY) 5 January (5) 29 December (363) 14 January (14) 5 January (5)

Days after flowering 23 25 23 27

Berry diameter when treatments applied (mm) 6.64 7.73 6.25 8.37

Values interpolated from mean curve fits for six vines for each cultivar/season. The curve that gave the lowest residual sum of squares was used: Gompertz curveswere fitted for budburst and logistic curves were fitted for flowering. DOY, day of the year; LA:FM, leaf area to fruit mass ratio.



ye b x m

=+{ }− −( )[ ]

100

1 (3)

y e e b x m

= −{ }− −( )[ ]100 (4)

where the value 100 corresponds to the maximum proportionfor any phenological stage, b corresponds to the rate constant, mis the inflection point on the curve and x is the day of the year(DOY). Lowest total residual sum of squares (the sum of allresidual sum of squares for each replicate fitted with a chosencurve) was used as the criterion of best curve fit. A Gompertzfunction provided the best fit for budburst and veraison, whilea logistic function performed better at flowering, assessed bytotal sum of squares (Table 2); per cent values, rates anddurations were interpolated from the fits of the models.

A three-parameter exponential growth function (Equation5, also known as the monomolecular equation) was used tomodel soluble solids accumulation, starting at 5°Brix; 8°Brixwas subsequently interpolated/extrapolated from the fit to esti-mate the time of veraison:

y a br x= + (5)

where a is the y asymptote, b < 0 and 0 < r < 1.Results were analysed by analysis of variance (ANOVA)

using Genstat 12 (VSN International Ltd, Hemel Hempstead,England). For veraison measurements, a two-way ANOVA (cropremoval × main leaf number per shoot) was conducted for eachcultivar. For yield and leaf parameters and the DOY of 8°Brixwere analysed by a three-way ANOVA (cultivar × cropremoval × main leaf number per shoot). Means separationswere determined by the Fisher’s unprotected least significantdifference method at the 5% level of significance.

Model fitting for model choice, parameter definition and8°Brix interpolations were completed using Genstat 12. Meansplots presented in figures were plotted using Sigmaplot 12(Systat Software, Inc., San Jose, CA, USA).

Results

Treatment timing and proportion crop removalBudburst (as interpolated as 50% average value of theGompertz curve fits) occurred at a similar time for Pinot Noir inboth seasons, but it was earlier in 2010/11 for Sauvignon Blanc

(Table 1). Flowering (as interpolated as 50% average value ofthe logistic curve fits) occurred later in 2009/10 for bothcultivars. When assessed at harvest, the proportion cropremoval achieved by the 50% removal treatments comparedwith the full crop treatment was slightly higher than the targetsin both seasons, with the exception of the six-leaf and 50% cropremoval treatment, in which the crop removal was lower (47%)in 2010 for Pinot Noir (Table 3). The 50% crop removal treat-ments also resulted in approximately half the bunch number ofthe full crop treatment, but the 75% crop removal treatmentsreduced the bunch number by only about two thirds comparedwith that on un-thinned vines (Table 3).

The influence of cultivar, main leaf number per shoot and cropremoval on yield and leaf parametersSauvignon Blanc berries were significantly heavier than those ofPinot Noir in both seasons (Tables 4,5). Crop removal had noeffect on the berry mass of either cultivar (P > 0.05 for main

Table 2. Total residual sum of squares values for all individual replicates fitted with Gompertz and logistic curves fits for budburst, floweringand veraison of Sauvignon Blanc and Pinot Noir vines in Marlborough, New Zealand.

n Gompertz Logistic

Pinot Noir Sauvignon Blanc Season total Total Pinot Noir Sauvignon Blanc Season total Total

Budburst

2009/10 6 526 92 618 638 572 71 643 748

2010/11 6 10 8 18 – 65 40 105 –

Flowering

2009/10 6 30 64 94 190 106 9 115 134

2010/11 6 34 62 96 – 3 16 19 –

Veraison

2009/10 24 2164 3364 5528 11 427 3851 2263 6115 14 123

2010/11 16 3364 2534 5899 – 5113 2895 8008 –

Totals in bold correspond to the curve fit that had the overall (total) lowest residual sum of squares for the stage. n, the number of replicates used for each stage; Seasontotal, the total residual sum of squares of the each curve fit summed for both cultivars across all replicates for each stage; Total, the total residual sum of squares forboth cultivars and both seasons for each phenological stage.

Table 3. Proportion of crop removed for Pinot Noir and SauvignonBlanc in the 2009/10 and 2010/11 seasons in Marlborough, NewZealand.

Cultivar Main leafnumber

per shoot†

Targetfruit mass

(% removal)

Actual fruitmass (% removed)‡

2009/10 2010/11

Pinot Noir 6 50 47 50

6 75 60 –

12 50 52 64

12 75 67 –

Sauvignon

Blanc

6 50 56 58

6 75 69 –

12 50 54 57

12 75 70 –

†Main leaf number refers to the number of leaves to which each shoot wastopped; ‡Actual proportion of fruit mass removed when measured at harvest.Values were calculated by dividing the mean yield measured at harvest of 50%of 75% crop removal treatments by the mean yield of each three vine replicate(no crop removal) at the same leaf number for each cultivar.



effect of crop removal). For leaf removal treatments, SauvignonBlanc vines with 12 leaves had heavier berries than those oftreatments with six leaves (in both seasons). In contrast, leafnumber had no significant effect on Pinot Noir berry mass(Tables 4,5).

Bunch mass was not significantly different between mosttreatments in 2009/10; the differences observed were not con-sistent for trends of decreased leaf area, crop removal or differ-ences between cultivars (Table 4). In 2010/11, Sauvignon Blancwith 12 leaves had significantly heavier bunches than Pinot Noirwith six leaves (Table 5).

In both seasons, for each treatment there was no differencein yield between cultivars (Tables 4,5). Yield was significantlyreduced by crop removal (50 or 75%) compared with that fromun-thinned vines, with no effect of leaf area in both seasons forboth cultivars (Tables 4,5).

In both seasons, trimming resulted in a significantdifference in leaf area, where the six-leaf treatments hadapproximately half the leaf area of the 12-leaf treatments(Tables 4,5). There was no difference in 12-leaf treatmentsbetween cultivars or six-leaf treatments between cultivars(Tables 4,5).

Table 4. Effect of cultivar, main leaf number per shoot and crop removal on grapevine yield and leaf parameters for 2009/10 season inMarlborough, New Zealand.


per shoot†

Proportionof crop

removed (%)‡

Bunches/vine

Average berrymass (g)

Average bunchmass (g)

Berries perbunch§

Yield(kg/m2)

Leaf area(m2/m)

LA : FM(m2/kg)

Pinot Noir 6 0 68c 1.47ab 112.5bcde 77c 4.10f 1.18a 0.29a

6 50 38b 1.46ab 94.1a 65ab 1.93bcde 1.03a 0.54ab

6 75 23a 1.53abc 94.3a 62a 1.16a 1.10a 0.98bc

12 0 69c 1.66c 106.1abcd 64ab 3.82f 1.72b 0.45a

12 50 35b 1.42a 104.6abc 74bc 1.98cde 1.94bc 0.99cd

12 75 24a 1.58bc 101.1ab 64ab 1.34ab 2.33d 1.85e

Sauvignon

Blanc

6 0 67c 1.86d 116.4bcde 63a 3.97f 1.08a 0.27a

6 50 38b 1.86d 116.1bcde 62a 2.24de 1.18a 0.54ab

6 75 24a 1.88d 122.9de 65ab 1.54abc 1.23a 0.80bc

12 0 72c 2.04e 118.7cde 58a 4.34f 2.13cd 0.51a

12 50 36b 2.09e 123.2e 59a 2.34e 2.35d 1.06cd

12 75 25a 2.10e 123.1e 59a 1.64abcd 2.04c 1.24d

LSD – – 6.22 0.156 16.9 10.8 0.610 0.274 0.277

SEM – – 2.16 0.054 5.86 3.77 0.212 0.095 0.097

Means within columns followed by different letters differ significantly from each other at P < 0.05 by the Fisher’s unprotected least significance difference (LSD) test.†Main leaf number refers to the number of leaves to which each shoot was topped. ‡Proportion of cropped removed corresponds to the amount relative to thenon-thinned vines (0% crop removal). §Calculated from the average berry mass measured for the 30-berry subsample taken at harvest and the yield at harvest.LA : FM, leaf area to fruit mass ratio; SEM, standard error of the mean.

Table 5. Effect of cultivar, main leaf number per shoot and crop removal on grapevine yield and leaf parameters for 2010/11 in Marlborough,New Zealand.


per shoot†

Proportionof crop

removed (%)‡

Bunches/vine

Averageberry

mass (g)

Averagebunch

mass (g)

Berries perbunch§

Yield(kg/m2)

Leaf area(m2/m)

LA : FM(m2/kg)

Pinot Noir 6 0 67b 1.57a 126.3ab 81 5.65b 1.19a 0.28a

6 50 36a 1.57a 119.5a 77 2.84a 1.11a 0.40bc

12 0 66b 1.70a 139.7bc 82 5.96b 2.39b 0.40bc

12 50 38a 1.73a 139.8bc 81 3.82a 2.66bc 0.72d

Sauvignon Blanc 6 0 68b 1.94b 143.3bc 74 5.21b 1.27a 0.25ab

6 50 39a 1.91b 153.1cd 81 3.04a 1.45a 0.49c

12 0 68b 2.23c 166.5d 75 5.97b 2.72bc 0.46c

12 50 40a 2.16c 159.4cd 74 3.38a 2.99c 0.91e

LSD – – 8.49 0.169 19.7 13.4 1.049 0.383 0.179

SEM – – 4.10 0.082 9.54 6.48 0.507 0.185 0.061

Means within columns followed by different letters differ significantly from each other at P < 0.05 by the Fisher’s unprotected least significance difference (LSD) test.†Main leaf number refers to the number of leaves to which each shoot was topped. ‡Proportion of cropped removed corresponds to the amount relative to thenon-thinned vines (0% crop removal). §Calculated from the average berry mass measured for the 30-berry subsample taken at harvest and the yield at harvest.LA : FM, leaf area to fruit mass ratio; SEM, standard error of the mean.



Equivalent ratios had the same LA : FM ratio when consid-ering each cultivar independently for both seasons (Tables 4,5).In 2010/11, the six-leaf full-crop treatments had a significantlylower LA : FM ratio than the 12-leaf full-crop treatments forboth cultivars (Table 4).

The influence of LA : FM ratio on veraison for Pinot NoirLeaf number and crop removal were both significant maineffects for 10 and 50% veraison dates for both seasons(P < 0.001 for leaf number in all cases except 10% veraison in2010/11, where P < 0.05; P < 0.01 for crop removal in all casesexcept 10% veraison in 2010/11, where P < 0.05); leaf number,however, had a predominant influence on the times of 10 and50% veraison (per cent total sum of squares 1.5–3 times greaterfor leaf removal than for crop removal in all cases except 10%veraison in 2010/11). Leaf number was also a more importantmain effect on duration, the time from 10 to 90% veraison(number of days) (P < 0.01) and the slope (parameter b)(P < 0.01 in 2009/10, P < 0.001 in 2010/11) of veraison devel-opment, with crop removal having a lesser effect on duration(P < 0.05 and non-significant in 2009/10 and 2010/11, respec-tively) and on b (P < 0.01); the per cent total sum of squares was1.5–3 times greater for leaf removal than for crop removal in allcases except duration in 2009/10. Interactions were not signifi-cant except at 10% veraison in 2009/10 (P < 0.05).

In 2009/10, comparison of means indicated that vines withsix leaves per shoot were significantly delayed (2 to 6 days later)for the time to reach 10% veraison compared with those with12 leaves (Table 6). Altering the LA : FM ratio by differentmeans (leaf removal vs crop removal) did not result in the sametiming of 10% veraison; the equivalent ratios of six-leaf 50%crop removal and 12-leaf 0% crop removal had similar effects(DOY for 10% veraison was 47 and 45 days, respectively), but12-leaf 50% crop removal resulted in earlier (3 days) 10%veraison than that for six-leaf 75% crop removal. Overall, thedelay due to reduced leaf number that was seen for 10%veraison was maintained through to 50% veraison, but equiva-lent ratios had the same timing of 50% veraison (Table 6).

For 2010/11, the results from means comparison supportedthe findings of 2009/10 season; however, in 2010/11, 50% crop

removal in combination with six leaves advanced veraison tothe same time as the 12-leaf full crop treatment, with bothtreatments reaching 10% veraison on 3 February (Table 6).

The six-leaf full crop treatment was the only treatmentwhere the duration, the time from 10 to 90% veraison, wassignificantly longer compared with that of all other treatmentsin 2009/10; in 2010/11, the 12-leaf 50% crop removal treat-ment resulted in the shortest duration of all treatments, signifi-cantly different from those of the six-leaf full crop treatment andsix-leaf 50% crop removal treatment. Among the other treat-ments, although there were no difference in the duration from10 to 90% veraison in 2009/10 and only a small difference in2010/11, the duration and shape of the curves defined by therate constant b were influenced predominantly by the leafnumber (Table 6, larger proportion of total sum of squares forleaf number for duration and b value in both seasons except forb in 2009/10).

The influence of LA : FM ratio on veraison for Sauvignon BlancReduced leaf number had a predominant main effect on thetime of veraison, delaying the start of veraison (10%) and 50%veraison (P < 0.001), accounting for approximately 50% of thetotal sum of squares for ANOVA in both seasons (Table 7). Cropremoval and interactions were not significant (P < 0.01), andneither main effect nor interaction influenced duration or thevalue of b (P < 0.05).

Comparison of means indicated that in the 2009/10 season,the six-leaf 75% crop removal treatment resulted in signifi-cantly earlier 50% veraison than the other six-leaf treatmentsbut no difference from all 12-leaf treatments (Table 7). Asobserved with Pinot Noir, equivalent ratios did not alwaysproduce the same results; the six-leaf and 50% crop removaltreatment delayed both 10 and 50% veraison in both seasonscompared with 12-leaf and 0% crop removal, confirming thatleaf area had a greater influence than crop removal on thetiming of veraison (Table 7). The timing of 10 and 50%veraison, however, was similar for the equivalent ratios of six-leaf 75% crop removal treatment and 12-leaf 50% crop removal(Table 7). The delay for six-leaf and full crop treated vines to

Table 6. Means comparisons for time and duration of veraison (from in-field colour change observations) for Pinot Noir in Marlborough, NewZealand. Mean dates, duration (the time to go from 10% veraison to 90% veraison) were interpolated from individual Gompertz curve fits of

each plot where y e e b x m= −{ }− −( )[ ]

100 .

Main leafnumberper shoot†

Proportionof crop

removed(%)‡

10% Veraison 50% Veraison Duration (days)(10–90% veraison)

b (rate ofdevelopment)

2009/10 2010/11 2009/10 2010/11 2009/10 2010/11 2009/10 2010/11

6 0 20 Feb d (51§) 9 Feb b (40) 27 Feb c (58) 19 Feb c (50) 18.2b 26.1b 0.186a 0.122a

50 16 Feb c (47) 3 Feb a (34) 21 Feb b (52) 12 Feb b (43) 11.4a 22.3b 0.276ab 0.145ab

75 16 Feb cd (47) –¶ 21 Feb b (52) – 11.9a – 0.273ab –

12 0 14 Feb bc (45) 3 Feb a (34) 18 Feb b (49) 10 Feb ab (41) 10.7a 18.6ab 0.312b 0.180b

50 13 Feb a (44) 2 Feb a (33) 16 Feb ab (47) 6 Feb a (37) 10.0a 12.6a 0.320b 0.247c

75 14 Feb abc (45) – 17 Feb ab (48) – 7.3a – 0.443c –

LSD – 2.12 4.50 3.78 5.04 5.63 7.78 0.112 0.051

SEM – 0.70 1.45 1.25 1.62 1.86 2.50 0.037 0.016

Means within columns followed by different letters differ significantly from each other at P < 0.05 by the Fisher’s unprotected least significance difference (LSD) test.†Main leaf number refers to the number of leaves to which each shoot was topped. ‡Proportion of cropped removed corresponds to the amount relative to thenon-thinned vines (0% crop removal). §Day of the year in parentheses (where 1 January = day one). b, a measure of the rate of development from the Gompertzcurve fit; SEM, standard error of the mean. ¶75% crop removal treatments were not repeated in the second season.



reach 10% veraison was 7 days in 2009/10 and 6 days in2010/11 compared with the time of 10% veraison for the ear-liest treatment (12-leaf 75% crop removal in 2009/10, 12-leaf50% crop removal in 2010/11); at 50% veraison, these differ-ences between the earliest and latest treatments were main-tained but were not augmented as observed for Pinot Noir(Table 6).

Soluble solids concentration of 8°Brix as a measure of onsetof maturationA soluble solids concentration of 8°Brix was used as a bench-mark value for the onset of maturation to enable a quantifiablecomparison between the two cultivars. Cultivar was the pre-dominant significant effect (P < 0.001), and then leaf numberaccounted for the next significant proportion of the total sum ofsquares for ANOVA (P < 0.001) and then crop removal (72% forcultivar, 8% for leaf removal and 4% for crop removal in 2009/10; 82% for cultivar, 10% for leaf removal and 4% for cropremoval in 2010/11). Leaf number by crop removal in 2009/10was the only significant interaction (P < 0.05). Regardless of theleaf or crop removal treatment, Sauvignon Blanc was alwayslater than Pinot Noir for the time to 8°Brix (Figure 1).

For Pinot Noir, comparison of means indicated that the dayin 2009/10 when soluble solids of 8°Brix was reached wasdelayed for six-leaf full crop treatment compared with the timein all other treatments (six and 12 leaves), with no differencebetween all other treatments (Figure 1a). In 2010/11, the six-leaf full crop treatment delayed the timing of 8°Brix, confirmingthe results of 2009/10; either leaf removal or retaining crop,however, delayed the day of reaching 8°Brix (Figure 1b). ForSauvignon Blanc in 2009/10, vines in the six-leaf full croptreatment were delayed in reaching 8°Brix compared with thosein all other treatments. Although vines in the six-leaf 50% cropremoval were earlier than those in the six-leaf full crop treat-ment, they were delayed compared with those in the six-leaf75% crop removal treatment and all 12-leaf treatments(Figure 1a); the results of 2010/11 confirmed the trends of2009/10 (Figure 1b). The equivalent ratios (12-leaf 100% cropremoval and six-leaf 50% crop removal treatments; 12-leaf

50% crop removal and six-leaf 75% crop removal treatments)were not statistically different from one another in both seasonsfor either cultivar except for 12-leaf and full crop compared withsix-leaf and 50% crop for Sauvignon Blanc in 2009/10(Figure 1).

Discussion

Leaf area removal influences the time of onset of maturationRestricting potential carbohydrate sources post-flowering byreducing leaf area via trimming can delay the onset of matura-tion, as measured by veraison (colour change for Pinot Noir andsoftness for Sauvignon Blanc), or as assessed using a benchmarksoluble solids concentration of 8°Brix. In contrast, crop removalhad little effect on the timing of the onset of fruit maturation.Therefore, when attempting to manipulate the time of veraison,it is important to consider the method of altering the ratio aswell as the actual LA : FM ratio. This probably reflects the factthat the fruit is only one of several sinks in the vine, while theleaf area is the main source of photosynthates. This is furtheremphasised when the relative source size is considered. For bothcultivars, when source size was large and less limiting (12leaves), removal of sinks via crop removal did not advanceveraison by all assessment methods except for the DOY to8°Brix for the 12-leaf 50% crop removal treatment ofSauvignon Blanc in 2010/11 (Tables 6,7 and Figure 1b). Sinksize became relevant only when source size was substantiallyreduced. The relative importance of leaf area therefore confirmsthe results obtained in leaf removal/trimming-only experimentson potted vines (Ollat and Gaudillere 1998, Petrie et al. 2000a).In New Zealand, current management practices do not trimcanopies to the same extent of the six-leaf full crop treatment;therefore, under current management practices, crop removalpost-fruitset may not achieve a substantial advancement inveraison. Manipulating carbohydrate availability via shoot trim-ming which reduces leaf area still offers a way to delay veraisonsubstantially for a given cultivar (up to 1 week for Pinot Noir).When the LA : FM ratio, however, is reduced for Pinot Noir, thedelay in the time to reach 8°Brix did not result in an overlap oftiming of the time to reach 8°Brix between Pinot Noir and

Table 7. Means comparisons for time and duration of veraison (from softness assessment) for Sauvignon Blanc in Marlborough, NewZealand. Mean dates, duration (the time to go from 10% veraison to 90% veraison) were interpolated from individual Gompertz curve fits of

each plot where y e e b x m= −{ }− −( )[ ]

100 .

Main leafnumber†

Proportionof cropremoval

(%)‡

10% Veraison 50% Veraison Duration (days)(10–90% veraison)

b (rate ofdevelopment)

2009/10 2010/11 2009/10 2010/11 2009/10 2010/11 2009/10 2010/11

6 0 25 Feb c (56§) 18 Feb b (49) 3 Mar b (62) 24 Feb b (55) 16.0 14.0 0.199 0.224

50 23 Feb bc (54) 16 Feb b (47) 1 Mar b (60) 21 Feb b (52) 15.1 14.3 0.219 0.234

75 20 Feb ab (51) –¶ 26 Feb a (57) – 15.9 – 0.202 –

12 0 18 Feb a (49) 12 Feb a (43) 26 Feb a (57) 16 Feb a (47) 20.4 12.0 0.160 0.258

50 18 Feb a (49) 12 Feb a (43) 24 Feb a (55) 16 Feb a (47) 17.1 11.0 0.183 0.316

75 18 Feb a (49) – 25 Feb a (56) – 18.3 – 0.173 –

LSD – 4.20 3.46 2.97 3.23 6.16 4.93 0.0638 0.135

SEM – 1.40 1.11 0.98 1.04 2.04 1.59 0.0212 0.043

Means within columns followed by different letters differ significantly from each other at P < 0.05 by the Fisher’s unprotected least significance difference (LSD) test.†Main leaf number refers to the main leaf number per shoot. ‡Proportion of cropped removed corresponds to the amount relative to the non-thinned vines (0% cropremoval). §Day of the year in parentheses (where 1 January = day one). b, a measure of the rate of development from the Gompertz curve fit; SEM, standard errorof the mean. ¶75% crop removal treatments were not repeated in the second season.



Sauvignon Blanc (Figure 1). This suggests that the interaction ofcultivar and temperature still predominantly drives the timingof different cultivars even in the presence of LA : FM ratiomanipulations.

Not only was the time of veraison delayed by leaf removal,but on severely source-limited Pinot Noir vines the duration ofveraison (from 10 to 90%) was longer, suggesting that therewould be greater variation in fruit composition at harvest(Table 6). This difference in fruit composition could potentiallylead to a difference in the aroma and flavour profiles in theresulting wine, even when harvested at the same meansoluble solids concentration. For Sauvignon Blanc, there wasno difference among treatments for the speed at whichveraison progressed (as measured by the duration from 10 to90% veraison or the rate constant b; Table 7); however, usinga count data scoring method, it is possible that small differ-ences were not detected that could otherwise be detected byassessing the proportion of colour change in the field on PinotNoir. Another possibility is that climate conditions pre-

veraison and during veraison may have been more favourablefor Sauvignon Blanc; thereby, veraison progressed faster thanthat for Pinot Noir.

Early leaf removal and yield parametersTopping or leaf removal applied early in the season, at variousstages up to E-L 31 (berries at pea size), can result in reducedyield because of a reduction in bunch mass or a reduction in thenumber of berries per bunch (Candolfi-Vasconcelos and Koblet1990, van Schalkwyk et al. 1995, Duchêne et al. 2003, Bennettet al. 2005, Poni et al. 2006, Lohitnavy et al. 2010). Thesechanges in yield responses have been correlated to a reducedfruitset, flower abscission or disruption of the fertilisationprocess resulting in more seedless berries (Candolfi-Vasconcelosand Koblet 1990, Lohitnavy et al. 2010) and a reduced berrysize (Ollat and Gaudillere 1998). The topping treatments appliedin this study were overall sufficiently late not to have altered theyield at harvest when considering yield parameters of the fullcrop treatments for six versus 12 main leaves. Intrieri et al.(2008) suggested that when berry mass and size are unaffectedby leaf removal, carbohydrate availability is not limited duringberry development. Our results indicated that for growthparameters, there was no difference in average bunch mass oryield between the 12-leaf and six-leaf treatments at the sameproportion of crop removal for each cultivar; but the averageberry mass was generally lower in all six-leaf treatments whencompared with that of the equivalent 12-leaf treatments(Tables 4,5). The delayed onset of maturation, however, meas-ured by 8°Brix with the low source treatments (six leaves),indicates that carbohydrate availability may have been limitingin the vine.

Even if some differences in average berry mass between six-and 12-leaf treatments were observed (Tables 4,5) (or differ-ences in average bunch mass for Sauvignon Blanc in 2010/11),all full crop treatments (at six or 12 leaves) within each seasonresulted in similar yields. From a practical perspective, if canopytrimming is used as a technique potentially to alter timing of thematuration period, this result indicates that early application,post-pea-size, may not confound the effect of canopy trimmingversus altered bunch parameters (bunch mass, berry size andnumber of berries per bunch) on the final yield itself.

Source–sink relationships in the grape vineWhile leaf removal and/or trimming shoots reduce the photo-synthetic source size, some increase in the rate of photosynthe-sis per unit leaf area can be expected. The extent to which theincrease in rate can cancel out the effect of the reduced leaf areawill largely depend on the amount of leaf area retained aftertrimming. Leaves were removed from the upper portion of theshoot in this study to reduce potential interaction with alteringbunch microclimate that can occur when lower leaves areremoved (Hunter and Visser 1990b, Guidoni et al. 2008). Byremoving upper leaves, however, that are still developing,potential sinks were also removed from the system. An increasein photosynthetic activity (and therefore compensation) canoccur when leaves are removed (Hunter and Visser 1988,1990b, Candolfi-Vasconcelos and Koblet 1991, Petrie et al.2003). Petrie et al. (2000c) showed that lower LA : FM ratio(source–sink ratios) were associated with a higher photosynthe-sis rate and a greater chlorophyll content, implying that activityis more related to vine source–sink balance rather than to leafage. Poni and Intrieri (2001) suggested that lower source activ-ity of big leaves is offset by source size, and Petrie et al. (2003)found that topping appeared to cause vines to use stored

Figure 1. Effect of proportion of crop removal and leaf removaltreatments applied after fruitset on the onset of maturation measuredas the day of the year to reach a soluble solids concentration of8°Brix in grapes of Pinot Noir and Sauvignon Blanc for the (a)2009/10 season and (b) 2010/11 season. Treatments are Pinot Noirsix main leaves per shoot (■); 12 main leaves per shoot ( );Sauvignon Blanc six main leaves per shoot ( ); and 12 main leavesper shoot ( ). Means with different letters differ significantly fromeach other at P < 0.05 by the Fisher’s unprotected least significantdifference test. Standard error of the mean 2009/10 = 0.709, stand-ard error of the mean 2010/11 = 0.742.



reserves to ripen fruit, but leaf removal in the fruiting zone didnot have this effect. It could be further hypothesised thatremoval of different portions of the canopy is likely to causesome photosynthetic compensation, but given that the basalleaves were measured to have a greater activity per unit area(Petrie et al. 2003), removal of this portion could potentiallydelay veraison even more under extreme source-limited condi-tions. Conversely, more sunlight and potential increased tem-perature in the bunch microclimate may be achieved, offsettingsome of this photosynthetic activity. Therefore, althoughremoval of different canopy portions would probably still shiftthe onset of maturation, a direct comparison would be neces-sary to elucidate to what extent this occurs for each method(basal leaf removal vs topping).

Lateral growth was eliminated in this experimental set up toremove one predominant competing sink during the time fromflowering to veraison. Developing fruit, trunk, nodes, shoots,canes and roots are also all potential sinks during this time,and vine size may confound the source–sink balance;Candolfi-Vasconcelos and Koblet (1990), however, indicatedthat leaf removal is more likely to cause reserve mobilisationthan increasing competition by the roots with other organs suchas bunches for carbohydrate source from the remaining leaves.Lateral shoot growth occurs concurrently with berry develop-ment. Consequently, lateral shoots can represent carbohydratesources and sinks depending on the time of development for thegrapevine: laterals would potentially act as competing carbohy-drate sinks during their growth; when lateral growth slowsdown, the lateral leaves may serve as carbohydrate sources forthe developing berries during maturation. Poni and Giachino(2000) observed that when Cabernet Sauvignon vines weretrained to four-bud spurs and either trimmed to six leaves, or 12leaves with or without lateral shoots and leaves, those vineswith laterals were able to compensate for the leaf area changesand were equivalent to the control treatments (no trimming).By eliminating lateral shoots in this current experiment, thevine has not been able to compensate photosynthetically via theproduction of a greater leaf area; any compensation would bethrough increased photosynthetic activity of existing leaves.Future studies investigating the role of lateral shoots and leaveson the timing of veraison would be of interest, especially toreflect what might occur under more commercial conditionsand to understand the competition of laterals as sinks or sourcesrelative to the berry development and phenological cycles.

If altering the LA : FM ratio was used as a strategy to delayor advance the maturation phase, long-term effects on budfertility, carbohydrate reserves and phenology in the subsequentseasons would also need to be considered. Previous research hasfound that defoliation led to reduced inflorescence number orberries per bunch, bunch size and or vine yield in the subse-quent season (Candolfi-Vasconcelos and Koblet 1990, vanSchalkwyk et al. 1995, Duchêne et al. 2003, Bennett et al. 2005,Poni et al. 2006, Lohitnavy et al. 2010). Further work isrequired to understand to what degree severely limiting carbo-hydrate supply through leaf removal, and the timing thereof, forthe objective of delaying fruit development would cause anadditive reduction in carbohydrate reserves over severalseasons. This is of even more importance in a cool climate wherepostharvest reserve accumulation is potentially less than that ofwarmer climates.

Maturity considerationsIn this research, the effect of changing the LA : FM ratio wasconsidered in terms of its effect on phenology; it is equally asimportant to understand the interaction effects of LA : FM ratio

manipulations on the evolution of key berry components gen-erally measured commercially, such as soluble solids accumula-tion, titratable acidity and pH. Stoll et al. (2011) suggested thepossibility of altered rates of sugar accumulation due to manipu-lation of the LA : FM ratio. Metabolites, such as anthocyanins,thiols, phenolic compounds and amino acids, also need to beconsidered when deciding on cultivar suitability and manipula-tion of the LA : FM ratio. For example, previous researchhas indicated for red cultivars that crop thinning increasesanthocyanins and phenolic substances (Guidoni et al. 2002,Petrie and Clingeleffer 2006), whereas reduced leaf areamanipulated up to veraison by trimming/hedging (rather thanbasal leaf removal, which has a confounding effect on changingsource–sink balance as well as bunch microclimate) reducesanthocyanins concentration (Reynolds and Wardle 1989).

ConclusionsRestricting potential carbohydrate sources by manipulating theLA : FM ratio by trimming post-flowering delays the onset ofmaturation in Sauvignon Blanc and Pinot Noir. Changing theLA : FM ratio by removing leaves could offer a solution fordelaying veraison, but only under extreme source-limited con-ditions could crop removal also alter this timing. The under-standing of the role of leaf area on timing of phenological eventswill open opportunities to model interactions of climate andvine management in the future.

AcknowledgementsThis work is part of the New Zealand Grape and Wine Researchprogram, a joint investment by PFR and NZ Winegrowers. Weappreciate the support of all institutions associated with theauthors of the paper and of Pernod Ricard New Zealand Ltdfor their assistance with the vineyard site and help in the field.The authors would like to acknowledge The Agricultural andMarketing Research and Development Trust, New Zealand, forthe scholarship to Amber K. Parker, and The Foundation forResearch Science and Technology (Designer Grapevines –CO6X0707) for their financial support.

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Manuscript received: 15 August 2013Revised manuscript received: 9 January 2014Accepted: 7 February 2014





Leaf area to fruit mass ratio determines the time of veraison in Sauvignon Blanc and Pinot Noir...

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