Effect of pruning system, cane size and season on inflorescenceprimordia initiation and inflorescence architecture of

Vitis vinifera L. Sauvignon Blanc

M. ELTOM1, C.S. WINEFIELD1 and M.C.T. TROUGHT2

1 Department of Wine, Food and Molecular Biosciences, Lincoln University, PO Box 84, Christchurch 7647, New Zealand2 Marlborough Wine Research Centre, The New Zealand Institute for Plant and Food Research Limited, PO Box 845,

Blenheim 7240, New ZealandCorresponding author: Dr Mark Eltom, email mark.eltom@lincolnuni.ac.nz

AbstractBackground and Aims: Inflorescence numbers per shoot and their size vary between seasons and may, within aseason, be affected by pruning systems, bud position along a cane and the size of the cane. A grapevine inflorescencetypically has a main rachis and a tendril, which may or may not have flowers (an outer arm). The aim of this studywas to identify the effect of these factors during inflorescence primordia (IP) initiation on the resulting number ofinflorescences per shoot and their architecture.Methods and Results: Two-cane, four-cane and spur-pruned Sauvignon Blanc vines were used to investigatechanges in inflorescence number, distribution and architecture over two growing seasons. The pruning system hadno effect on the inflorescence number per shoot (fruitfulness), inflorescence architecture or distribution at a givencane node number. There were differences in inflorescence number and structure between the seasons, likelyassociated with air temperatures during primordia initiation. A warmer initiation period was associated with anincrease in the occurrence of flowers on the outer arm and lower positions of the basal inflorescences (shoot budposition). An increase in cane cross-sectional area correlated to an increase in fruitfulness and an increase in theaverage occurrence of an outer arm with flowers along a cane.Conclusions: Inflorescence number, the position of the basal inflorescence on the developing shoot and thedevelopment of the outer arm are affected by the bud position of the shoot along a cane, the cross-sectional area ofthe cane and the season. Our results suggest that initiation of IP may occur at the same time for all bud positionsalong a shoot, so long as they are free from inhibiting factors.Significance of the Study: Cane selection can be used to modify inflorescence number and architecture and thusthe potential yield of grapevines.

Keywords: cane size, grapevine, inflorescence primordia architecture, outer arm, pruning, Sauvignon Blanc

IntroductionInflorescence primordia (IP) are derived from anlagen (a groupof uncommitted cells) during the growing season precedingtheir appearance (season one) (Pratt 1971, Srinivasan andMullins 1981). The number of IP formed per bud (fruitfulness)within and between seasons has been shown to be influencedby differences in weather conditions, in particular temperatureand light intensity during their initiation and development(Baldwin 1964, Buttrose 1969a, 1970, MacGregor 2002,Sanchez and Dokoozlian 2005, Trought 2005).

The development of an IP into its inner and outer arm (theprimary branch point on the main rachis) components is alsosensitive to temperature during IP initiation (Watt et al. 2008). Ithas also been demonstrated that branching of IP continues afterinitiation until dormancy in season one (Pratt 1971, Srinivasanand Mullins 1981, Morrison 1991), where the degree of branch-ing may be influenced by temperature during this period (Palmaand Jackson 1981, Dunn and Martin 2007). The research men-tioned above, however, typically examines inflorescence struc-

tures as a whole, leaving a gap in the literature concerning theinfluence of temperature on outer arm development.

In addition to temperature and light, the size of the cane caninfluence the final number of inflorescence structures per shoot(Thomas and Barnard 1937, Antcliff et al. 1958, Sommer et al.2000, Jones et al. 2013, Eltom et al. 2014). Jones et al. (2013)demonstrated a positive linear relationship between cane starchconcentration and the mass of the cane. Starch concentrationwas also correlated with the final average inflorescence numberper bud along a cane. Likewise, we have shown (Eltom et al.2014) a positive linear relationship between the volume of thecane and its total carbohydrate (CHO) content. Limiting CHOavailability by girdling canes shortly before budbreak resulted inthe termination of some of the pre-formed inflorescences, adecrease in flower numbers per inflorescence structure and adecrease in the occurrence of an outer arm with flowers (Eltomet al. 2014).

The acropetal timing of latent bud and IP development(Snyder 1933, Pratt 1971, Srinivasan and Mullins 1981,

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Swanepoel and Archer 1988) can result in IP at different posi-tions along the developing shoot experiencing varying environ-mental conditions during initiation. This is frequently (but notalways) observed as an increase in bud and subsequent shootfruitfulness as bud positions along the cane increase to amaximum value around bud numbers seven to ten. This is,however, dependent on the cultivar and environmental condi-tions during IP development (Antcliff et al. 1958, Buttrose1969a,b, 1974, Sommer et al. 2000, Jones et al. 2013). As well,the acropetal development of buds and IP is likely to result in adecrease in flower number per inflorescence structure as shootbud position increases (Keller et al. 2010, McLoughlin et al.2011, Eltom et al. 2014). The consequence, however, of budand IP acropetal development on the presence of an outer armwith flowers has received no attention. Thus, the purpose of thisstudy was to identify the influence of pruning system, budposition and the size of the cane on IP number and developmentin two contrasting seasons.

Materials and methods

Plant materialVitis vinifera L. Sauvignon Blanc vines (SO4 rootstock), locatedon a commercial vineyard, Marlborough, New Zealand (−41.53°latitude, −173.88° longitude), were used for this study. Vineswere planted in a north-south orientation, 1.8 m between thevines and 2.4 m between the rows. The pruning systems used inthis trial were part of a larger training system trial established in2003. The training systems were established on whole rows(approximately 120 m long), randomly distributed within fourreplicate blocks. Four rows per training system were used forthis study. Vines were pruned during the winter as follows: (i) abilateral trained cordon spur-pruned to retain two buds per spurand ten spurs per vine; (ii) head trained four-cane, ten buds percane (40 buds per vine); and (iii) head trained two-cane (20buds per vine). Shoots were retained in a vertical position withtwo foliage wires, and vines were trimmed two or three timesduring the season, at a height of 2.0 m from the ground and0.5 m between the vertical faces of the canopy. Leaves wereremoved at approximately 3 weeks post fruitset on both sides ofthe canopy to achieve approximately 30–40% bunch exposure.Twelve, six and three vines per row were selected for analysiswithin each of the rows at random for the two-cane and four-cane head trained and for the spur-pruning systems, respec-tively, where each cane (n = 96) or bud was considered to be aseparate replicate. See Jackson (1997) for in-depth descriptionsand diagrams of grapevine pruning systems.

Measurement of inflorescence architecture and canecross-sectional areaApproximately 2 weeks before flowering, the number of inflo-rescences and their position on shoots, as well as the structureobserved at the outer arm position (an outer arm with flowers,a tendril or no structure), were recorded at every cane nodenumber. Because of the oval shape of grapevine canes in cross-section, two measurements of the diameter (the widest andnarrowest) were made between the first and second basal budswith a digital calliper (0.01-mm resolution) and used to calcu-late the cross-sectional area of the cane.

Meteorological measurementsThe air temperature was recorded on a TinyTag (Gemini DataLoggers, Chichester, England) temperature logger located in aplastic Stevenson screen 1.4 m from the ground in the vineyard.Solar radiation and rainfall were recorded at the Marlborough

regional weather station approximately 7 km from the experi-mental site (http://www.mrc.org.nz/). Heat units, expressed asgrowing degree days (GDDs, base temperature of 10°C and noupper limit), were determined by calculating the growingdegree units per hour, then averaging all 24-h values to give thedaily GDD value.

Regressions and statistical analysisAll statistical analysis was undertaken with GenStat Edition12.1 (VSN International Ltd., Hemel Hempstead, England).Within and between treatments were subjected to one-wayanalysis of variance (ANOVA) tests to determine P-values andto check if the data were normally distributed. Fisher’s unpro-tected least significant difference test (at a significance level ofP < 0.05) was used post hoc to separate within and betweentreatment and season effects from one another. Regressionswith groups were carried out between treatments and years todetermine if multiple data sets were represented by statisticallysimilar regressions.

ResultsThe period from 11 December to 17 January the following yearis hypothesised to be the period of time when temperatureexerts its greatest influence on IP initiation for Sauvignon Blancin Marlborough (Trought 2005). Although the start and enddate of IP initiation will probably depend on seasonal condi-tions, these dates represent the most accurate long-term studyof when IP initiation is probably occurring for Sauvignon Blancin Marlborough. The average daily temperature and radiationduring this period were 18.3 and 16.7°C and 24.0 and23.5 MJ/m2 during the 2010/11 and the 2011/12 seasons,respectively. Accumulated rainfall values during the sameperiods were 132 and 94 mm, respectively (see SupportingInformation Figure S1).

Inflorescence number per shoot at each cane node numberwas compared between pruning systems and seasons usingANOVA. When pruning systems were compared in each season,the average inflorescence number per shoot for a given canenode number was statistically similar (P > 0.05; Figure 1). Therewas, however, a statistically significant difference (P < 0.05) inaverage inflorescence number per shoot between seasons. Apolynomial regression with groups (using each pruning systemfor each year as a separate group) was used to fit cane nodenumber versus average inflorescence number (Figure 1). Thepruning system had no effect on the inflorescence number pershoot at the same cane node number (P > 0.05), and budnumbers could thus be grouped together in a single regressionfor each year. The 2 years were represented by statisticallyseparate (P < 0.01) parallel lines. On average, there wereapproximately 0.4 more inflorescences per shoot at each budposition in the 2011/12 season than in the 2012/13 season.Inflorescence number increased from cane node number one toa maximum at approximately cane node number six in bothgrowing seasons.

The relationship between cane cross-sectional area versusthe average inflorescence number per shoot along a cane, andthe proportion of basal inflorescences along a cane that had anouter arm with flowers was analysed by grouping cane cross-sectional area in increments of 10 mm2 (Figures 2,3). Polyno-mial regressions with groups (using each pruning system foreach year as separate groups) were used to fit these relation-ships. The regression with groups indicated that the threepruning systems had no influence on the number or structure ofthe inflorescences (P > 0.05), and these could be grouped

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together in a single regression for each year, respectively. Theaverage inflorescence number per shoot increased as cane cross-sectional area increased, and the 2 years were represented bystatistically separate (P < 0.01) parallel lines (Figure 2). As well,

the proportion of basal bunches that had an outer arm withflowers increased as cane cross-sectional area increased, wherethe 2 years were represented by statistically separate (P < 0.01)lines (Figure 3).

The position of the basal and apical inflorescences on thedeveloping shoot was analysed with ANOVA. Pruning systems (atthe same cane node number) had no effect on the basal or apicalinflorescence position on the shoot (P > 0.05; Figure 4). Theshoot positions of basal inflorescences, however, at all cane nodenumbers (P < 0.01) in 2011/12 were lower than that in the2012/13 season. In contrast, the positions of the apical inflores-cences were similar at all cane node numbers in both seasons. Aregression with groups (using each pruning system for each yearas separate groups, basal and apical data separately) was used tofit the average inflorescence position versus cane node number.The shoot bud positions of basal inflorescences were representedby statistically separate (P < 0.01) parallel lines between the twoseasons. The shoot bud positions of apical inflorescences wererepresented by the same line (P > 0.05).

There was an approximately 48% decrease in the presenceof an outer arm with flowers and an equivalent increase in thepresence of a tendril in the 2012/13 growing season comparedwith that in the 2011/12 growing season, when averagedacross all shoot bud positions (Table 1). In both growingseasons, as the position of the inflorescence increased on adeveloping shoot, the occurrence of an outer arm decreasedand the occurrence of a tendril increased. Additionally, therewas a statistically significant increase in the presence of anouter arm in the basal inflorescence position as cane budincreased (P < 0.05, data not shown). This was a reflection ofthe lower position of the basal inflorescence as cane nodenumber increased (Figure 4).

Figure 1. Effect of grapevine cane node number on the averagenumber of inflorescences per shoot for the 2011/12 season( , , ▲) and for the 2012/13 season ( , , ). Regression withgroups for the 2011/12 growing season ( ), y = 1.3 + 0.77 ×[1 – exp(−0.55 × x)], R2 = 0.94, P < 0.05; and for the 2012/13growing season ( ), y = 0.85 + 0.77 × [1 – exp(−0.55 × x)],R2 = 0.86, P < 0.05. Vines were pruned to two canes ( , ), fourcanes ( , ) or spur-pruned (▲, ). Data points represent meanvalues. Vertical error bars represents the least significant difference(LSD) (P < 0.05) at each cane node number.

Figure 2. Effect of grapevine cane cross-sectional area on theaverage number of inflorescences per shoot along a cane for the2011/12 season ( , , ) and for the 2012/13 season ( , , ).Regression with groups for the 2011/12 growing season ( ),y = −2.29 × 10−5x2 + 0.0098x + 1.22, R2 = 0.92, P < 0.05; and for the2012/13 growing season ( ), y = −2.29 × 10−5x2 + 0.0098x +0.77, R2 = 0.95, P < 0.05. Vines were pruned to two canes ( , ),four canes ( , ) or spur-pruned ( , ). Cane cross-sectional areawas calculated between basal buds two and three, and was groupedin 10 mm2 increments. Average number of inflorescences along thecane was calculated by adding the number of inflorescences for eachshoot along a cane together, then dividing by the number of shootsalong the cane. Frequency = number of measurements in each sizegrouping.

Figure 3. Effect of grapevine cane cross-sectional area on theaverage proportion of basal inflorescences along a cane with anouter arm for the 2011/12 season ( , , ) and for the 2012/13season ( , , ). Regression with groups for the 2011/12 grow-ing season ( ), y = −9.4 × 10−6x2 + 0.0036x + 0.63, R2 = 0.86,P < 0.05; and for the 2012/13 growing season ( ), y = −9.6 ×10−6x2 + 0.0079x−0.17, R2 = 0.94, P < 0.05. Vines were pruned totwo canes ( , ), four canes ( , ) or spur-pruned ( , ). Canecross-sectional area was calculated between basal buds two andthree and was grouped in 10 mm2 increments. The average propor-tion of basal inflorescences along a cane with an outer arm wascalculated by counting the number of basal inflorescences along acane that had an outer arm present divided by the total number ofshoots along a cane.

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DiscussionVariation in IP number, architecture and position on a shootbetween seasons was examined using two-cane, four-cane andspur-pruned V. vinifera L. Sauvignon Blanc vines. The pruningregime had no influence on the fruitfulness per bud or on theoccurrence of an outer arm with flowers at a given cane nodenumber. However, because of the decreased fruitfulness of thefirst two basal buds, the overall fruitfulness of a spur-prunedsystem (which is essentially a two-bud cane) was lower thanthat of a ten-bud cane-pruned vine. This result is consistentwith previous research that indicates that pruning systems ofsimilar design will not have a significant difference in fruitful-ness (Sommer et al. 2000, Reynolds and Vanden Heuvel 2009).Additionally, thinner canes resulted in a decrease in inflores-cence number per shoot and in the proportion of those inflo-

rescences with flowers on the outer arm regardless of thepruning system. Thus, the inflorescence number per shoot maybe reduced if the training system results in thinner, less vigorousshoots.

When the two seasons were compared, there were markeddifferences in inflorescence number per shoot and inflorescencearchitecture. Solar radiation over the proposed initiation periodwas similar in both seasons. In contrast, there was a 1.6°Cdifference in the average daily temperature. MacGregor (2002)indicated that this would be sufficient to cause a similar differ-ence in inflorescence number per shoot on spur-pruned Char-donnay vines.

Our study is the first to indicate that cane cross-sectionalarea can partially compensate for differences in inflorescencenumber and architecture between seasons. The occurrence ofan outer arm with flowers was more sensitive to cane cross-sectional area when temperature during IP initiation was cooler.An increase in cane cross-sectional area from 25 to 75 mm2

resulted in a 243% increase in outer arms with flowers in2012/13 versus a 38% increase in 2011/12. However, the 60%increase in inflorescence number per shoot along the cane wasconsistent between the two seasons (Figures 2,3). To overcomeseasonal differences completely, canes greater than the averagesize would need to be selected. This suggests that selecting largercanes at pruning may, in part, increase potential inflorescencenumber and size, particularly following a cool initiation period.An alternative to cane selection by size could be the retention ofextra canes, as recommended for Sultana vines (Antcliff et al.1958). The positive correlation between the increase in inflo-rescence number or occurrence of an outer arm with flowers ascane cross-sectional area increased cannot be explained directlyby our results. Current research, however, has indicated that theCHO content of a cane, or its proportion of starch, is correlatedto its volume (Eltom et al. 2013) or mass (Jones et al. 2013).Therefore, cane cross-sectional area may be an indicator of theCHO status of the cane/vine, which is consistent with previousresearch (Thomas and Barnard 1937, Sommer et al. 2000).

The buds at cane node number ten versus one had anincrease in fruitfulness and in the proportion of outer arms withflowers (Figures 2,3). Traditionally, this is explained by theacropetal development of buds along a shoot, resulting in budsat bud ten initiating later and during warmer and/or moresunny conditions (Snyder 1933, Pratt 1971, Srinivasan andMullins 1981, Morrison 1991). Temperature alone, however,cannot account for these differences, as buds at bud one have agreater time to develop, which should result in an increasedfruitfulness and branching of IP compared with that of the budat bud ten. As well, the increase in the shoot bud position ofbasal inflorescence at lower cane node numbers (those closest tothe head of the vine) requires an explanation.

To aid in our explanation, we propose two concepts con-cerning IP initiation. The first concept is that IP initiation occursat the same time for all latent buds on a shoot, not in anacropetal gradient. The signal for initiation is probably a result ofa threshold being met, as research in temperature-controlledenvironments indicates that there is a minimum temperaturerequirement for IP initiation (Buttrose 1969b, 1970, Sanchezand Dokoozlian 2005). The second concept is that when thesignal for IP initiation occurs, the IP initiate at the first budposition available in the latent bud that is sufficiently distal tothe inhibiting effect of the shoot apical meristem (Prusinkiewiczet al. 2009, Peer et al. 2011).

The proposed concepts, as well as previous research thatindicates that soon after a leaf appears on a shoot, the latent budat that bud position begins to develop (Pratt 1971, Srinivasan

Figure 4. Effect of grapevine cane node number on the averagebasal and apical inflorescence position on a shoot (a) for the 2011/12season and (b) the 2012/2013 season; basal ( , , ) and apical( , , ) inflorescences for the two-cane ( , ), four-cane( , ) and spur-pruned vines ( , ), respectively. Basal inflores-cence position versus cane node number is represented by parallelregressions with between the two growing seasons: (a) 2011/12,y = 3.3 – 0.3lnx, R2 = 0.89; and (b) 2012/13, y = 3.7 – 0.3lnx,R2 = 0.86. Apical inflorescence position versus cane node numberfor the 2011/12 and the 2012/13 seasons is represented by the sameregression, y = 4.5x, R2 = 0.79 and 0.84 for the 2011/12 and the2012/13 seasons, respectively. Data points represent mean values.Vertical error bars represents the least significant difference (LSD)(P < 0.05) at each cane node number.

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and Mullins 1981), may explain the observed decrease in thebasal inflorescence shoot position as cane node numberincreases. When the signal for IP initiation occurs, the latent budat shoot bud position one will have more bud positions devel-oped than the latent bud at shoot bud position ten. This causesan increase in the basal inflorescence insertion position at shootbud position one because the first available bud position in thelatent bud is more apically located than the latent bud at shootbud position ten. Additionally, during a warmer initiationperiod, the signal for IP initiation probably occurs earlier in thedevelopment of the latent buds, and hence there is a decrease inthe basal inflorescence insertion position compared with thatduring a cooler initiation period. A depiction of this change inprocess between a warm and cool initiation period is outlined inFigure 5.

While plant growth regulators were not measured in thisstudy, these compounds have an important influence on IPinitiation, fruitfulness and the subsequent inflorescence archi-tecture. For example, the initiation and development of an IP isunder the control of auxin, cytokinins, strigolactones and theirassociated biochemical pathways (Srinivasan and Mullins 1979,Carmona et al. 2008, Crane et al. 2012). Branching of a shootand IP structures is inhibited by the apical meristem through theproduction and transport of auxin (Prusinkiewicz et al. 2009).In contrast, when auxin concentration is low, branching isstimulated by cytokinins (Mueller and Leyser 2011, Peer et al.2011, He et al. 2012). Thus IP close to the apical meristem willpotentially undergo less branching than basal IP in part becauseof the proximity of an auxin source. Further understanding ofthe actions of plant growth regulators on inflorescence structureand their interactions with IP position, growth, shoot develop-ment and environmental conditions is needed to developour understanding of mechanisms controlling grapevine yieldpotential.

ConclusionsSeasonal conditions influence the number of IP formed per budand their architecture. The pruning systems had no statisticallysignificant effect on the fruitfulness per shoot, the distribution ofthe IP along a shoot or on the development of an outer arm withflowers at a given cane node number. The spur-pruned vines,however, had an overall decrease in fruitfulness, reflecting the

lower inflorescence number when shoots arise from cane nodenumbers one and two, compared with that of shoots arising atgreater cane node numbers. Cane selection is a tool that can beused to alter fruitfulness and inflorescence architecture within aseason. We hypothesise that IP initiation occurs at all bud posi-tions along a shoot once a threshold is met, as long as the IP aresufficiently distal to the inhibitory influence of the apicalmeristem.

AcknowledgementsThis study was funded by The New Zealand Institute for Plantand Food Research Limited and a Lincoln University writingscholarship. The financial support of New Zealand Winegrowersto our wider grape and wine research program is appreciated.

Table 1. Proportion of the occurrence of an outer arm, tendril or no structure for inflorescences between the twoseasons as a function of shoot bud position.

Occurrence of outer arm, tendril or no structure (%)

1† 2 3 4 5 6

2011/12 growing season

Outer arm n/a 95.4 e/4 86.6 d/3 42.8 b/2 17.6 c/1 0.0

Tendril n/a 1.0 a/1 8.3 a/2 51.6 c/3 75.7 d/4 92.9 c/5

Nothing n/a 3.6 ab/ns 5.1 a/ns 5.6 a/ns 6.7 b/ns 7.1 b/ns

2012/13 growing season

Outer arm n/a 79.0 d/4 54.1 c/3 5.9 a/2 0.6 a/1 0.0

Tendril n/a 13.7 c/1 40.1 b/2 88.6 d/3 95.0 e/4 96.4 d/4

Nothing n/a 7.3 b/ns 5.8 a/ns 5.5 a/ns 4.4 a/ns 3.6 a/ns

Values are means of all pruning regimes. Values were separated using Fisher’s unprotected least significant difference (LSD) test followinganalysis of variance (ANOVA), where values with different letters (between structures for a given shoot bud number) and numbers(between shoot bud numbers for a given structure) are statistically different from one another (P < 0.05). Note that these findings wereindependent of the cane node number. †Shoot bud position. n/a, no sample available; ns, not significant (P > 0.05).

Figure 5. A schematic representation of the developing latentgrapevine buds at shoot bud positions one versus ten when thetheoretical inflorescence primordia (IP) initiation temperaturethreshold is met. The figure depicts the acropetal development of IPin latent buds at shoot bud positions one and ten. n = shoot budposition as well as the bud number in the developing latent buds.Figure adapted from Carmona et al. (2002).

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We gratefully acknowledge the use of vines at Villa MariaWines, New Zealand, and for the helpful editorial commentsfrom Dr Anne Gunson.

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Manuscript received: 18 September 2013

Revised manuscript received: 28 April 2014

Accepted: 14 May 2014

Supporting informationAdditional Supporting Information may be found in the onlineversion of this article at the publisher’s web-site: http://onlinelibrary.wiley.com/doi/10.1111/ajgw.12097/abstract

Figure S1. (a) Average daily temperature; (b) cumulativegrowing degree days (CGDDs, base 10°C); (c) daily solar radia-tion (MJ/m2); and (d) daily rainfall (mm). The areas highlightedin a black box are the dates in which grapevine inflorescenceprimordia initiation is proposed to be most susceptible to theinfluence of temperature. 2010/11 initiation temperature forthe 2011/12 growing season ( ); and 2011/12 initiation tem-perature for the 2012/13 growing season ( ).

464 Season and inflorescence architecture Australian Journal of Grape and Wine Research 20, 459–464, 2014

© 2014 Australian Society of Viticulture and Oenology Inc.