Reproductive performance of Cabernet Sauvignon and Merlot ... · reproductive performance. This study assessed the reproductive performance of Cabernet Sauvignon and Merlot grafted

Reproductive performance of Cabernet Sauvignon and Merlot(Vitis vinifera L.) is affected when grafted to rootstocks

C.M. KIDMAN1,2, P.R. DRY1,3, M.G. MCCARTHY1,4 and C. COLLINS1

1 School of Agriculture, Food and Wine, The University of Adelaide, Waite Research Institute, PMB 1, Glen Osmond,SA 5064, Australia

2 Wynns Coonawarra Estate, Memorial Drive, Coonawarra, SA 5263, Australia3 The Australian Wine Research Institute, Wine Innovation Cluster, Glen Osmond, SA 5064, Australia4 South Australian Research and Development Institute, Research Road, Nuriootpa, SA 5355, Australia

Corresponding author: Dr Cassandra Collins, email [email protected]

AbstractBackground and Aims: Cabernet Sauvignon and Merlot are Vitis vinifera cultivars known to be susceptible to poorfruitset in cool climates (MJT 19°C–20.9°C). The importance of rootstocks in viticulture is well documented,particularly in relation to yield, salinity and water relations; little is known, however, about how rootstocks affectreproductive performance. This study assessed the reproductive performance of Cabernet Sauvignon and Merlotgrafted to rootstocks.Methods and Results: Cabernet Sauvignon and Merlot grafted to rootstocks, Ramsey, 5C Teleki, Schwarzmann and1103 Paulsen, were assessed for reproductive performance over three consecutive growing seasons. This wasmeasured by assessing the following: bud fruitfulness, flower number per inflorescence, fruitset (%), berry numberper bunch, coulure index (CI), and millerandage index (MI). Fruitset was higher when grafted to rootstockscompared to that of ungrafted vines which corresponded to a decrease in MI and CI. For Cabernet Sauvignon, therewere no observed differences in fruitset, however, fruitfulness and bunch number were higher when grafted torootstocks compared to ungrafted vines.Conclusion: Rootstocks affect fruitfulness and fruitset in Cabernet Sauvignon and Merlot, however, reproductiveperformance differs between cultivars when grafted to the same rootstock.Significance of the Study: Rootstocks may be used as a management tool to manipulate the reproductiveperformance of Cabernet Sauvignon and Merlot in cool climates.

Keywords: flower number, fruitfulness, fruitset, reproductive performance, rootstock

IntroductionThe process of reproductive development in grapevines can bedivided into several sequential stages that occur over two suc-cessive growing seasons. As a consequence, the growth andsuccess of the crop is dependent on bunch initiation in theprevious season, inflorescence development, flowering andfruitset and the development of seeds and flesh within a grapeberry in the current season. Factors affecting these processesmay include the cultivar (Longbottom 2007, Dry et al. 2010),climatic conditions (Buttrose 1969, Dunn and Martin 2000,Sommer et al. 2000, 2001), excessive vigour or shading (Dry2000, Collins et al. 2006) and choice of rootstock through aneffect on scion vigour (Candolfi-Vasconcelos and Castagnoli1995, Cirami 1999, Whiting 2003, Dry 2007, Candolfi-Vasconcelos et al. 2009, Keller et al. 2011).

There are several ways that reproductive performance canbe measured in grapevines. For example, bud fruitfulness can beestimated prior to budburst by a measure of the number ofinflorescence primordia present in a compound bud (Buttrose1969). Other parameters used to measure reproductive devel-opment include fruitset, millerandage and coulure (Dry et al.2010). Fruitset is a measure of the number of flowers thatsuccessfully develop into berries. In some instances, berries onan inflorescence may not develop seeds or only develop seed

traces (May 2004). These seedless berries are smaller in size thanseeded berries yet still undergo veraison and ripen normally(May 2004). Seedless berries generally account for a low pro-portion of total berry mass approximately 0.9% in CabernetSauvignon and 2% in Chardonnay (Collins and Dry 2009), butin Merlot, seedless berries may account for approximately 10%of all berries (Longbottom 2007).

In contrast, live green ovaries (LGOs), which are formedafter pollination, but without fertilisation, are seedless or maycontain only seed traces, remain small, green and hard andmake up less than 1% of total bunch mass (Friend et al.2003, Longbottom 2007, Collins and Dry 2009). Therefore,the relative proportion of seeded and seedless berries andLGOs on a bunch is indicative of grapevine reproductiveperformance.

Millerandage and coulure are important reproductive phe-nomena of fruitset as they can have a negative impact on finalyield (Dry et al. 2010). Millerandage occurs when flowersdevelop abnormally into either seedless berries or LGOs (May2004, Collins and Dry 2009). Coulure results when flowersfail to develop into a berry or LGO, also defined as excessiveshedding of ovaries or young berries (May 2004, Collins andDry 2009). Coulure can result from a deficiency in the concen-tration of soluble and insoluble sugars and may be caused by a

Kidman et al. Reproductive performance of grafted grapevines 1

doi: 10.1111/ajgw.12032© 2013 Australian Society of Viticulture and Oenology Inc.

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disturbance in the concentration of growth regulators (Lebonet al. 2008). To measure the expression of coulure andmillerandage, two indices have been developed: millerandageindex (MI) and coulure index (CI) (Collins and Dry 2009). Forboth indices, the higher the numerical value, the greater theincidence of the condition. Poor fruitset can result from varia-tion in temperature, nutrition, growth regulators, carbohydratereserves, cultural practices and water stress (Alexander 1965,Ebadi et al. 1995, May 2004, Longbottom 2007, Lebon et al.2008, Collins and Dry 2009, Dry et al. 2010). The classificationof wine grapes based on reproductive parameters revealed thatcertain cultivars were more susceptible to poor fruitset thanothers (Dry et al. 2010). Cabernet Sauvignon and Merlot havebeen grouped together as they are both susceptible to poorfruitset due to a high incidence of both millerandage andcoulure (May 2004, Longbottom 2007, Dry et al. 2010).

Propagation of a scion with a rootstock results in a graftedvine, and ungrafted vines differ from grafted vines due to thedevelopment of the graft union (Tandonnet et al. 2010). Theformation of callus tissue and vascular tissue from the graftingprocess house the newly formed xylem and phloem vessels thatmaintain the flow of solutes between the scion and the root-stock (Nicholas 1992, May 1994). Tandonnet et al. (2010) sug-gested that the interaction between the combined scion androotstock may have a greater effect than the rootstock effectalone. In some combinations, rootstock genotype has beenshown to influence biomass allocation between roots andshoots, while in other combinations the scion genotype had aninfluence on shoot development of grafted vines. Tandonnetet al. (2010) also concluded that root development includingroot length and root system structure of rootstock genotypes isstrongly influenced by scion genotype.

Reproductive development of grapevines may potentially bemanaged through the use of rootstocks (Candolfi-Vasconcelosand Castagnoli 1995, Cirami 1999, Whiting 2003, May 2004,Dry 2007). For example, fruitfulness of the scion has been foundto increase or decrease depending on the rootstock to whichthe scion was grafted (Hedberg et al. 1986, Sommer et al. 2000,2001, Keller et al. 2001, 2011, Stevens et al. 2008, Candolfi-Vasconcelos et al. 2009). An attempt to classify rootstocksaccording to their fruitset potential has been previously reportedby several authors (Candolfi-Vasconcelos and Castagnoli 1995,Cirami 1999, Whiting 2003, May 2004, Dry 2007, Keller et al.2011). Candolfi-Vasconcelos and Castagnoli (1995) reportedthat rootstocks significantly improved fruitset of Pinot Noirvines at two of five sites investigated in the Oregon WineRegion, USA. Wrattonbully has been previously described ashaving poor fruitset for red cultivars with lower berry numberper bunch as a consequence (Phylloxera and Grape IndustryBoard of South Australia 2012). More recent studies contradictprevious reports inferring that rootstock may have no effect onfruitset and that the interaction between the scion and therootstock is greater than the rootstock effect alone (Tandonnetet al. 2010, Keller et al. 2011).

The aim of this study was to assess reproductive perfor-mance of Cabernet Sauvignon and Merlot grafted to four root-stocks. In addition, a V. vinifera control was included for the twocultivars to further assess the differences between grafted andnon-grafted vines.

Materials and methods

Experimental siteThe experimental site was in Wrattonbully, South Australia,Australia (37°02’ 27.62”S, 140°52’ 09.87”E). The mean January

temperature (MJT) for Wrattonbully is 19.6°C and the degreedays (DD) (October–April) is 1421 (Longbottom et al. 2011).This is comparable to other cool climate regions, such as theYarra Valley (MJT 19.3°C, DD 1489) and Coonawarra (19.6°C,DD 1396) (Coombe and Dry 1988). The vineyard was planted in2002 at 1818 vines per hectare, with vine spacing and rowspacing at 2 m × 2.75 m, respectively, and was trained to abilateral cordon with vertical shoot positioned canopy. Allgrafted and ungrafted vines were sourced from YalumbaNursery, South Australia, Australia. All certified clones (CW44and D3V14) and rootstocks were tested for viruses and otherdiseases and have corresponding class and source identificationas well as batch number for traceability. Prior to grafting usingthe Omega graft technique, rootstocks were hot water treatedfor a period of 30 min at 50°C. All vines were planted on thesame day as potted one-year-old vines, selected from thenursery specifically for vine uniformity and size.

The vineyard had an elevation of 83 m. Vines were spurpruned by hand to approximately 40 nodes per vine to matchthe commercial pruning level of the vineyard. Vines were dripirrigated, using an underground water source (bore). Schedul-ing of irrigation was based on Gbug (gypsum block) sensorassessments, and irrigation was approximately 1.4 mL/ha(140 mm) each season. Meteorological conditions were moni-tored using daily temperature and rainfall data sourced from theBureau of Meteorology weather station at Naracoorte Airport,located approximately 6 km to the west of the trial site. Long-term average temperature, growing degree days (GDD) andrainfall data were calculated from weather data archived onthe Bureau of Meteorology website (http://www.bom.gov.au/climate/dwo/IDCJDW5044.latest.shtml).

The long-term average rainfall for the region is561 mm (http://www.bom.gov.au/climate/dwo/IDCJDW5044.latest.shtml). The site is located within a phylloxera-free regionthat allows for the planting of ungrafted V. vinifera vines. The soilis a mixture of loamy sand over red clay on calcrete; mediumthickness loamy sand over a well structured red clay on calcrete,with areas of exposed red clay on calcrete (Longbottom et al.2011).

Experimental designVitis vinifera L. cultivars Merlot (clone D3V14) and CabernetSauvignon (clone CW44) were grafted to four American Vitisrootstocks: Ramsey (Vitis champinii), 5C Teleki (Vitis berlandieri XVitis rupestris), Schwarzmann (Vitis riparia X Vitis rupestris) and1103 Paulsen (Vitis berlandieri X Vitis rupestris) and comparedwith ungrafted Merlot and Cabernet Sauvignon. A completelyrandomised block design of four rootstock treatments and oneungrafted control with five replicates of one vine per plot wasused at the vineyard. Measurements were taken over threeconsecutive seasons starting in the 2008/09 growing season.

Vegetative and reproductive measurementsDuring winter dormancy, cane number and pruning mass wererecorded, and average cane mass determined from these meas-ures. All variables are presented on a per metre of cordon basis.Twenty canes from each plot were also collected at this time toassess bud fertility. Compound buds at node positions one tofour on each cane were dissected and scored for the number ofinflorescence primordia (IP) and the presence of primary budnecrosis (PBN) using a binocular microscope (Leica – modelMS5, Leica Microsystems, Wetzlar, Germany) at 10–40 × mag-nification. The number of IP per compound bud was recorded inthe primary (N+2) bud; however, when the primary bud was

2 Reproductive performance of grafted grapevines Australian Journal of Grape and Wine Research 2013

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necrotic, then the largest secondary (N+3) bud was scored forthe number of IP. An average of the number of IP at nodes oneto four was determined to give an indication of the potentialfruitfulness per node. Primary bud necrosis was also assessed ateach node, and the incidence expressed as a proportion. Actualfruitfulness per shoot was determined by the number of inflo-rescences per metre of cordon divided by the total number ofshoots (count plus non count) per metre of cordon at pruningtime to give a mean number of inflorescences per shoot. No buddissection results were obtained for the first season of the trial(2008/09) due to a contamination of samples which renderedthe analysis inconclusive.

To assess fruitset, three inflorescences per vine from fivevines per treatment were randomly selected and enclosed in afine mesh bag prior to flowering. After flowering, bags wereremoved and the dehisced caps of the flowers in each bag werecounted to determine flower number per inflorescence. Corre-sponding bunches were collected to determine berry numberper bunch on the same day as harvest. The bunch number andmass of reference bunches were included in the final vine yieldmeasurement. Berries within each reference bunch wereassessed for the proportion of seeded berries, seedless berriesand live green ovaries (LGOs) while average mass was deter-mined as the mass of the bunch (g) divided by the sum of seededberries and seedless berries on the bunch. At harvest, allbunches were counted, and the total number of bunches pervine were weighed and recorded. Results are reported permetre of cordon. Yield components and fruitset indices werecalculated according to formulae in Collins and Dry (2009): totalberry number per bunch, fruitset (%), coulure index (CI),millerandage index (MI), berry mass (g), fruit yield per metrecordon.

Statistical analysesEach cultivar was subjected to a one-way factorial with repeatedmeasures analysis of variance (ANOVA), using Genstat Version10.2 (Lawes Agriculture Trust 2007, Rothamsted, England). Theinteraction between cultivar x season x rootstock treatment wasassessed by ANOVA and principal component analysis (PCA) inMicrosoft Excel 2007 and XLSTAT Version 2012 1.01 (AddinsoftSARL, Paris, France). Details of individual analyses are providedin the text or captions.

Results

Climatic conditions over three seasonsOver the three seasons, temperature at budburst, flowering dateand length of flowering period differed between cultivars andseasons. The flowering period corresponded to the modifiedEichhorn and Lorenz (E–L) stages 19–25 (Coombe 1995).Budburst and flowering was earlier for Merlot than for CabernetSauvignon in every season (Figure 1). The interval betweenbudburst and flowering was 57 to 67 days for Merlot and 54 to59 days for Cabernet Sauvignon. The flowering period forMerlot and Cabernet Sauvignon ranged from 7 to 10 days and 6to 11 days, respectively, across the three seasons.

In 2009, the average temperature at flowering (E-L 19–25)was 18.2°C compared to 16.1°C for Cabernet Sauvignon, andflowering took 7 days for Merlot and 6 days for CabernetSauvignon. For the 2010 flowering period, average tempera-ture was 22.8°C for Merlot and 22.2°C for Cabernet Sauvignonand took 11 days for Merlot and 8 days for CabernetSauvignon. In 2011, flowering lasted for 9 days for Merlot atan average temperature of 18°C and 11 days for CabernetSauvignon at an average temperature of 20.3°C. In addition,

Cabernet Sauvignon had 40 mm of rainfall throughout thisperiod. (http://www.bom.gov.au/climate/dwo/IDCJDW5044.latest.shtml). The summation of growing degree days (GDD)(base 10°C) from budburst to flowering was assessed forboth cultivars: GDD was higher in 2009 than in either 2010 or2011. For Merlot, 2010 had the lowest GDD of 176 calculatedfrom budburst to flowering than the other seasons – 247 in2009 and 223 in 2011 – whereas for Cabernet Sauvignon, 2011had the lowest GDD summation of 261 from budburst toflowering than 297 in 2009 and 265 in 2010. Annual rainfallfor the growing seasons 2009, 2010 and 2011 (seasons werecalculated from 12 September to 31 March) was 182, 242,439 mm, respectively. The summation of rainfall from bud-burst to flowering was 129, 155 and 205 mm, respectively(Figure 1).

Vine growthPruning mass for Cabernet Sauvignon ranged from 0.46 kg/mcordon to 1.26 kg/m cordon with a mean mass of0.78 kg/m cordon. For Merlot, pruning mass ranged from0.27 kg/m cordon to 0.75 kg/m cordon with a mean massof 0.42 kg/m of cordon (Tables 1 and 2). Pruning mass is aproduct of cane mass and cane number; there was, however, astronger relationship observed for pruning mass and averagecane mass (R2 = 0.781) than for pruning mass and canenumber (R2 = 0.545). Pruning mass was lowest in 2009,0.57 kg/m and 0.35 kg/m of cordon for Cabernet Sauvignonand Merlot, respectively, and highest in 2011, 1.0 kg/m and0.51 kg/m of cordon for Cabernet Sauvignon and Merlot,respectively. Cabernet Sauvignon vines grafted to Ramsey hada pruning mass higher than that of ungrafted vines (Table 1).Cane mass was also higher for vines grafted to 5C Teleki,Ramsey and Schwarzmann than for ungrafted vines. In con-trast, Merlot vines grafted to 1103 Paulsen, Ramsey (and in thefinal year, Schwarzmann) had a pruning mass higher than thatof ungrafted and 5C Teleki. Cane mass was higher for 1103Paulsen and Ramsey than for ungrafted vines, and canenumber was also higher for 1103 Paulsen in 2010 and 2011than for ungrafted vines (Table 3).

A significant seasonal effect on yield was found for bothcultivars. Yield was significantly lower in 2009 than 2010(Tables 1 and 2). Cabernet Sauvignon grafted to Schwarzmannhad consistently higher yield in each season than that of theother rootstocks (Table 1). For Merlot, 1103 Paulsen andRamsey had a yield significantly higher than that of ungraftedvines and 5C Teleki (Table 2).

There was no significant effect of rootstock or season onthe ratio of fruit mass/pruning mass (FM/PM) of CabernetSauvignon (Table 1). Merlot vines grafted to Schwarzmann in2011, however, had a significantly higher FM/PM than all othertreatments (Table 2).

Reproductive performanceBud fertility. Cabernet Sauvignon vines grafted to 5CTeleki had lower potential fruitfulness than for all otherrootstocks. For actual fruitfulness, 5C Teleki was lower onlythan Schwarzmann. Schwarzmann had an actual fruitfulnesshigher than that of the other rootstocks (Table 3). UngraftedCabernet Sauvignon had an actual fruitfulness significantlylower than that of 1103 Paulsen, Ramsey and Schwarzmann(Table 3).

In Merlot, potential fruitfulness was higher in 2010 than in2011. Potential fruitfulness was lower for 5C Teleki and 1103





Paulsen than Ramsey in 2011. Actual fruitfulness was signifi-cantly lower in 2010 than in the other seasons, and 2009 wassignificantly higher than preceding seasons (Table 4).

Rootstock type had no effect on the incidence of PBN forCabernet Sauvignon. There was a significant influence of season

on PBN: higher in 2011 than in 2010 (Table 3). In contrast, asignificant rootstock x season interaction was observed for PBNwith Merlot. In 2010, ungrafted vines, and Ramsey had a lowerincidence of PBN than 5C Teleki and 1103 Paulsen; but in 2011,there was no effect of rootstock (Table 4).

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Figure 1. Daily rainfall (■) and average temperature (maximum + minimum temperature/2) (◆) at 80% flowering for the (a) 2008, (b) 2009and (c) 2010 seasons for Cabernet Sauvignon and Merlot at Wrattonbully, SA, Australia.



Fruitset. For both cultivars, flower number per inflorescencewas highest in 2011 (Tables 3 and 5). Flower number forCabernet Sauvignon was significantly higher for 5C Teleki thanfor ungrafted vines (Table 3). For Merlot, a significant season xrootstock interaction for flower number was observed althoughthere were no distinct differences between rootstocks over eachof the three seasons. In 2009, 1103 Paulsen and 5C Teleki hadsignificantly higher flower number than Ramsey and ungraftedvines. In 2010, there was no significant difference in flowernumber and in 2011, 1103 Paulsen had significantly lowerflower number than ungrafted, Ramsey and Schwarzmannvines (Table 5).

Fruitset was significantly affected by rootstock treatment forMerlot (Table 5). Fruitset of ungrafted Merlot was significantlylower than that for all other rootstocks: 41% higher for Ramsey,57% for Schwarzmann, 63% for 1103 Paulsen and 75% for 5CTeleki.

For Cabernet Sauvignon, with the exception of flowernumber, no significant difference between rootstock treatmentswas observed for seeded berry number, total berry number,LGOs, MI, CI, bunch mass or berry mass (Table S1). For Merlot,seeded berry number was consistently lower for the ungraftedvines than rootstocks (Table 5). A significant rootstock x seasoninteraction was also observed for total berry number andnumber of LGOs (Table 5). Total berry number was significantly

higher for 1103 Paulsen than the ungrafted vines in 2009. In2010, 5C Teleki, Ramsey and Schwarzmann had a higher berrynumber than the ungrafted, whereas in 2011, Ramsey and 5CTeleki had higher berry numbers than ungrafted. Large seasonalvariation in the number of LGOs was observed, but no clearpattern between rootstocks was apparent. In 2010 and 2011, thenumber of LGOs was lower than 2009.

Although Cabernet Sauvignon showed no rootstock effectfor fruitset, CI or MI, the opposite was true for Merlot—CI andMI values for ungrafted vines were 19–33% and 11–33%higher, respectively, than the rootstock treatments. Merlotgrafted to Ramsey and 5C Teleki had significantly higher berrymass than both ungrafted and 1103 Paulsen. In addition, Merlotbunch mass was significantly lower for ungrafted than 5CTeleki, Ramsey and Schwarzmann (Table 5).

Season, cultivar and rootstock interactionNo significant interaction was found between cultivar x root-stock x season (Table 6). However, there were significant inter-actions for rootstock x cultivar and cultivar x season for thefollowing variables: actual fruitfulness, PBN, seeded and seed-less berries, yield and fruit mass/pruning mass (FM/PM). Thenumber of seeded berries was significantly higher for Merlotthan Cabernet Sauvignon. In all three seasons, Merlot had sig-nificantly higher yield, FM/PM and lower MI than Cabernet

Table 1. Effect of rootstock and season on vine growth measures for Cabernet Sauvignon grown in Wrattonbully in the 2009, 2010 and 2011growing seasons.

Variable Season Treatment P-value LSD (5%)

Control(CAS)

1103Paulsen

5C Teleki Ramsey Schwarzmann Seasonmean

Pruning mass

(kg/metre

cordon)

2009 0.6 0.5 0.6 0.7 0.6 0.6a 0.018(R) 0.13(R)

2010 0.6 0.7 0.8 0.8 0.8 0.8b <0.001(S) 0.07(S)

2011 0.9 1.0 1.0 1.2 1.0 1.0c NS(R*S) NS(R*S)

Treatment mean 0.7a 0.7a 0.8ab 0.9b 0.8ab

Cane mass (g) 2009 31 30 45 35 30 34a <0.001(R) 6.15(R)

2010 35 39 58 55 45 47b <0.001(S) 4.48(S)

2011 39 45 59 63 51 51b NS(R*S) NS(R*S)

Treatment mean 35a 38ab 54c 51c 42b

Cane no. 2009 19def 16bc 13a 19def 20ef 17a <0.001(R) 1.49(R)

2010 17bcd 16bc 15ab 15ab 19def 17a <0.001(S) 1.06(S)

2011 24h 22gh 18cde 20ef 21fg 21b 0.004(R*S) 2.42(R*S)

Treatment mean 20 18 15 17 19

Yield (kg/metre

cordon)

2009 0.9a 1.3abc 1.0ab 1.3abcd 1.7cd 1.3a 0.006(R) 0.39(R)

2010 2.0de 1.6bcd 2.6e 1.7cd 2.6e 2.1b <0.001(S) 0.40(S)

2011 2.5e 2.4e 1.5abcd 1.7bcd 2.8e 2.2b 0.004(R*S) 0.65(R*S)

Treatment mean 1.8 1.7 1.7 1.6 2.4

FM/PM† 2009 2.8 3.0 1.4 1.7 3.0 2.4 NS(R) NS(R)

2010 3.7 2.8 3.3 2.7 3.2 3.1 NS(S) NS(S)

2011 1.8 3.0 2.6 2.2 3.5 2.6 NS(R*S) NS(R*S)

Treatment mean 2.7 2.9 2.4 2.1 3.2

Statistical significance of the effects of rootstocks on Cabernet Sauvignon is given by P < 0.05(*), P < 0.01(**), P < 0.001(***) and not significant (NS). For alltreatments and seasons, each value represents the mean of five replicate samples for each group. The 5% LSD values listed are for comparison treatments (R) andfor comparison seasons (S). Where there were no significant (R x S) interactions, the treatment means were compared using the (R) 5% LSD, and the season meanswere compared using the (S) 5% LSD. Letters account for significant differences among treatments. †Fruit mass/Pruning mass is the yield divided by the pruning massper metre of cordon. CAS, Cabernet Sauvignon; LSD, least significant difference.



Sauvignon, and Cabernet Sauvignon had higher flowernumbers than Merlot (Table 6).

Principal component analysis was used to assess the inter-action between cultivar and rootstock for variables that werefound to be significantly different (Table 6). Principal compo-nent analysis was performed on the aggregated data and PC1and PC2 accounted for 90.4% of the variation (Figure 2). InPC1, yield was highly correlated with bunch mass, fruitset andseeded berry number and negatively correlated with MI and CI.The scores for the two cultivars and five rootstock treatmentswere also projected onto the vector biplot. Cabernet Sauvignonhad higher pruning mass, cane mass, cane number, MI andCI than Merlot. Cabernet Sauvignon grafted to Ramsey,Schwarzmann and 5C Teleki had higher pruning mass, canemass and cane number than ungrafted and 1103 Paulsen vines.Merlot grafted to rootstocks had higher yield, seeded berries,bunch mass and fruitset than Cabernet Sauvignon and theungrafted Merlot.

DiscussionThis study has confirmed the influence of rootstock type onreproductive development for Merlot and Cabernet Sauvignon.This is one of the few studies where reproductive performancehas been assessed on scions grafted onto non-vinifera rootstockvs ungrafted V. vinifera. For the measures of reproductive per-

formance, rootstock effect differed between the two scioncultivars. The influence of rootstock on reproductive perfor-mance and yield in Cabernet Sauvignon was mainly due to aneffect on fruitfulness. In contrast, a combination of fruitfulness,fruitset and bunch mass differences influenced yield in Merlot.

Effect of climateSite temperature at both budburst and flowering differedbetween seasons and cultivars. Previously, a lower temperatureat budburst has been reported to increase the number of flowerson a grapevine inflorescence (Dunn and Martin 2000). Further-more, floral induction in response to environmental conditionssuch as low temperature has been reported in other species(Kinet et al. 1993). Mean temperature at budburst for Merlotand Cabernet Sauvignon was lower in 2011 than in previousseasons, and for both cultivars, budburst was delayed comparedto 2009 and 2010. This delayed budburst was due to a coolerand wetter start than the previous seasons. Environmental con-ditions at budburst have been shown to affect the degree ofbranching of the inflorescence primordium, and this can affectflower development (May 2000). The variation in flowernumbers can be explained by the number of branches on theinflorescence (Dunn and Martin 2000). Previous studies haveshown that a cooler temperature at budburst of ≤12°C hasbeen found to promote flower formation, whereas a warmer

Table 2. Effect of rootstock and season on vine growth measures for Merlot grown in Wrattonbully in the 2009, 2010 and 2011 growingseasons.

Variable Season Treatment P-value LSD (5%)

Control(MER)

1103Paulsen


Pruning mass

(kg/metre

cordon)

2009 0.28a 0.48de 0.28a 0.40cd 0.33ab 0.4a <0.001(R) 0.081(R)

2010 0.27a 0.55e 0.35ab 0.45d 0.35ab 0.4a <0.001(S) 0.033(S)

2011 0.36bc 0.75f 0.40cd 0.53e 0.53e 0.5b 0.024(R*S) 0.099(R*S)

Treatment mean 0.3 0.6 0.3 0.5 0.4

Cane mass (g) 2009 20 35 29 27 24 26a <0.001(R) 2.24(R)

2010 21 34 26 30 28 28a <0.001(S) 4.52(S)

2011 30 47 36 42 40 39b NS(R*S) NS(R*S)

Treatment mean 24a 38d 30b 33c 31b

Cane no. 2009 14bcd 15cd 10a 15cd 14bc 14 0.010(R) 1.96(R)

2010 13bc 16d 14bc 15cd 13bc 14 NS(S) NS(S)

2011 13ab 16d 12ab 13abc 13bc 13 0.003(R*S) 2.35(R*S)


Yield (kg/metre

cordon)

2009 2.1 4.4 2.7 3.3 3.2 3.1a 0.004(R) 1.0(R)

2010 1.5 3.1 2.6 3.9 2.7 2.8a <0.001(S) 0.40(S)

2011 5.0 7.1 4.9 6.5 5.2 5.7b NS(R*S) NS(R*S)

Treatment mean 2.9a 4.9c 3.4a 4.6bc 3.7ab

FM/PM† 2009 14.2c 9.7abc 13.0bc 12.0abc 10.0abc 11.9b NS(R) NS(R)

2010 5.4a 6.2ab 7.7abc 9.1abc 7.4abc 7.2a 0.01(S) 3.11(S)

2011 8.8abc 9.1abc 9.6abc 8.5abc 22.0d 11.6b 0.028(R*S) 7.14(R*S)

Treatment mean 9.5 8.3 10.1 10.0 13.2

Statistical significance of the effects of rootstocks on Merlot is given by P < 0.05(*), P < 0.01(**), P < 0.001(***) and not significant (NS). For all treatments and seasons,each value represents the mean of five replicate samples for each group. The 5% LSD values listed are for comparison treatments (R) and for comparison seasons (S).Where there were no significant (R x S) interactions, the treatment means were compared using the (R) 5% LSD and the season means were compared using the(S) 5% LSD. Letters account for significant differences among treatments. †Fruit mass/Pruning mass is the yield divided by the pruning weight per metre of cordon.LSD, least significant difference; MER, Merlot.



temperature ≥25°C reduces flower formation. Inflorescences onlater bursting shoots are known to have fewer flowers than onearlier bursting shoots due to the progressive increase in soil andair temperature over time (Dunn and Martin 2000). The coolerbudburst weather resulted in significantly higher flowernumbers for both cultivars in the 2011 season.

Flowering of individual clusters has been reported to extendfor between 4 and 8 days under optimal conditions but maybe delayed due to cool or wet conditions (May 2004,Candolfi-Vasconcelos et al. 2009). In 2011, flowering occurredat an average temperature of 18°C for Merlot and 20°C forCabernet Sauvignon, and although temperature was optimal at

Table 3. Effect of rootstocks and season on fruitfulness, flower number and incidence of Primary Bud Necrosis (PBN) for CabernetSauvignon grown in Wrattonbully.

Variable Season Treatment P-value 5% LSD

Control(CAS)

1103Paulsen

5C Teleki Ramsey Schwarz-mann Seasonmean

Potential fruitfulness† 2009 – – – – – 0.02(R) 0.18(R)

2010 1.72 1.82 1.36 1.81 1.76 1.69 NS(S) NS(S)

2011 1.79 1.79 1.65 1.70 1.64 1.71 NS(R*S) NS(R*S)

Treatment mean 1.75b 1.80b 1.51a 1.75b 1.70b

% PBN† 2009 – – – – – NS(R) NS(R)

2010 2 9 8 10 10 8a 0.002(S) 0.05(S)

2011 16 15 30 11 10 17b NS(R*S) NS(R*S)


Actual fruitfulness‡ 2009 2.07 2.37 1.77 2.25 2.73 2.24c 0.001(R) 0.28(R)

2010 1.33 1.95 1.67 1.87 2.06 1.78b <0.001(S) 0.20(S)

2011 1.07 1.38 1.63 1.38 1.78 1.45a NS(R*S) 0.46(R*S)

Treatment mean 1.49a 1.90c 1.69abc 1.83bc 2.19d

One-way ANOVA was performed using repeated measures analysis to assess the interaction between rootstock and season. The comparison of both cultivars ontreatments over three seasons is given by P < 0.05(*), P < 0.01(**), P < 0.001(***) and not significant (NS). Letters account for significant differences amongtreatments. For all cultivars, treatments and seasons, each value represents the mean of five replicate samples for each group. †Calculations of fruitfulness and PBNare determined on a per node basis. ‡Actual fruitfulness was calculated by number of inflorescences per metre of cordon divided by canes per metre of cordon. CAS,Cabernet Sauvignon; LSD, least significant difference.

Table 4. Effect of rootstock and season on fruitfulness and incidence of Primary Bud Necrosis (PBN) (%) for Merlot grown in Wrattonbully.


Control(MER)

1103Paulsen

5C Teleki Ramsey Schwarz Seasonmean

Potential

fruitfulness†

2009 – – – – – – NS(R) NS(R)

2010 1.79ab 1.91b 1.74ab 1.75ab 1.91b 1.82b 0.01(S) 0.09(S)

2011 1.74ab 1.54a 1.52a 1.87b 1.75ab 1.69a 0.049(R*S) 0.23(R*S)

Treatment mean 1.77 1.74 1.63 1.81 1.83

% PBN† 2009 – – – – – – NS(R) NS(R)

2010 5a 18bc 20c 4a 10abc 11 NS(S) NS(S)

2011 9abc 5a 11abc 15abc 6.2ab 9 0.01(R*S) 0.113(R*S)


Actual

fruitfulness‡

2009 2.62 2.28 2.13 2.51 2.21 2.35c NS(R) NS(R)

2010 1.41 1.54 1.48 1.95 1.76 1.63a <0.001(S) 0.06(S)

2011 1.78 2.00 2.05 1.88 1.82 1.91b NS(R*S) NS(R*S)

Treatment mean 1.94 1.94 1.89 2.11 1.93

One-way ANOVA was performed using repeated measures analysis to assess the interaction between rootstock and season. The comparison of both cultivars ontreatments over three seasons is given by P < 0.05(*), P < 0.01(**), P < 0.001(***) and not significant (NS). Letters account for significant differences amongtreatments. For all cultivars, treatments and seasons, each value represents the mean of five replicate samples for each group. †Calculations of fruitfulness and PBNare determined on a per node basis. ‡Actual fruitfulness was calculated by number of inflorescences per metre of cordon divided by canes per metre of cordon. LSD,least significant difference; MER, Merlot.



Table 5. Effect of rootstock and season on reproductive performance for Merlot grown in Wrattonbully in 2009, 2010 and 2011 seasons.


Control(MER)

1103Paulsen


Flower no.† 2009 224abc 307def 262cde 180ab 253bcd 245b NS(R) NS(R)

2010 196abc 164a 185ab 195abc 218abc 192a <0.001(S) 33.3(S)

2011 418h 314def 362efgh 369fgh 392gh 371c 0.019(R*S) 79.7(R*S)

Treatment mean 279 262 270 248 288

Seeded berry

no.†

2009 66abc 122fg 88cde 45a 102efg 85 <0.001(R) 18.3(R)

2010 53ab 68abcd 87cde 91cdef 90cde 78 NS(S) NS(S)

2011 61abc 82bcde 97defg 109efg 123g 95 <0.001(R*S) 31.3(R*S)


Seedless berry

no.†

2009 19 16 17 8 20 16a NS(R) NS(R)

2010 23 35 30 19 19 25b 0.002(S) 5.47(S)

2011 15 14 18 20 15 16a NS(R*S) NS(R*S)


LGO no.† 2009 13cd 24e 16d 8bc 25e 17b 0.010(R) 3.75(R)

2010 1a 2a 1a 1a 1a 1a <0.001(S) 3.44(S)

2011 0a 1 a 1a 1a 1a 1a 0.025(R*S) 7.49(R*S)


Total berry

no.†

2009 85abc 139e 105bcde 53a 122de 101 <0.001(R) 19.33(R)

2010 76ab 103bcd 117cde 110cde 108bcde 103 NS(S) NS(S)

2011 76ab 97bcd 115cde 129de 138e 111 <0.001(R*S) 33.3(R*S)


% fruitset 2009 30 49 51 32 50 42b <0.001(R) 7.98(R)

2010 41 64 71 59 53 57c <0.001(S) 6.45(S)

2011 20 34 36 37 39 33a NS(R*S) NS(R*S)

Treatment mean 30a 49bc 53c 42b 47bc

CI 2009 6.6 4.0 4.4 6.2 3.7 5.0b <0.001(R) 0.84(R)

2010 5.8 3.4 2.9 4.0 4.6 4.2a <0.001(S) 0.65(S)

2011 8.0 6.5 6.3 6.3 6.1 6.6c NS(R*S) NS(R*S)

Treatment mean 6.8c 4.7ab 4.6a 5.5b 4.8ab

MI 2009 3.2cde 2.5bcd 2.6bcde 2.4bcd 3.4de 2.8b 0.012(R) 0.56(R)

2010 3.4de 3.6e 2.6bcde 1.8ab 1.8ab 2.6b <0.001(S) 0.45(S)

2011 2.1abc 1.6ab 1.9ab 1.6ab 1.2a 1.7a 0.021(R*S) 1.0(R*S)

Treatment mean 2.9c 2.5bc 2.3ab 1.9a 2.1ab

Bunch mass

(g)

2009 80 147 176 135 128 133a 0.03(R) 45.1(R)

2010 79 103 164 131 124 120a 0.006(S) 22.7(S)

2011 98 131 181 170 214 159b NS(R*S) NS(R*S)

Treatment mean 86a 127ab 174c 145bc 155bc

Berry mass

(g)

2009 1.12 1.02 1.2 1.68 1.45 1.31ab 0.015(R) 0.22(R)

2010 0.99 0.99 1.4 1.27 1.17 1.18a 0.044(S) 0.16(S)

2011 1.32 1.34 1.5 1.31 1.43 1.34b NS(R*S) 0.48(R*S)

Treatment mean 1.10a 1.10a 1.40b 1.50b 1.30ab

Statistical significance of the effects of rootstocks on Merlot is given by P < 0.05(*), P < 0.01(**), P < 0.001(***) and not significant (ns). For all treatments and seasons,each value represents the mean of five replicate samples for each group. The 5% LSD values listed are for comparison treatments (R) and for comparison seasons (S).Where there were no significant (R x S) interactions, the treatment means were compared using the (R) 5% LSD and the season means were compared using the(S) 5% LSD. Letters account for significant differences among treatments. †Per bunch. CI, Coulure Index; LGO, live green ovary; LSD, least significant difference; MER,Merlot; MI, Millerandage Index; NS, not statistically significant difference among means at a 0.05 level.



EL 19–25, 40 mm of rainfall was experienced for CabernetSauvignon at this time which may have contributed to the delayin flowering for Cabernet Sauvignon and contributed to higherCI and lower fruitset. Rain can be detrimental to fruitset atflowering as it prevents the dehiscence of the cap on flowers,and this delays ovule fertilisation (May 2004). The increase inflower number for both cultivars corresponded to a high pro-portion of flowers that were unable to set fruit or develop intoberries (seeded or seedless) or LGOs and was observed to cor-

relate with a strong inverse relationship (R2 = 0.982) betweenCI and fruitset for 2011. Vasconcelos and Castagnoli (2000) alsofound an inverse relationship between flower number andfruitset. Mυller Thurgau grafted to 5C Teleki has been reportedto have a high flower number, but the functionality of theseflowers was lower and coulure higher than that for other root-stocks in the trial (Keller et al. 2001). Cabernet Sauvignongrafted to 5C Teleki also had a higher flower number than thatof ungrafted vines, but this had no effect on the incidence of CI.

Table 6. Analysis of variance (ANOVA) for the interactions between season x cultivar x rootstock for all parameters measured at Wrattonbullyin 2009, 2010 and 2011 seasons.

Variable Cultivar Rootstock Season Cultivar xrootstock

Cultivar xseason

Rootstock xseason

Cultivar xrootstock x

season

Pruning mass (kg/m

canopy)

P-value <0.001 0.004 <0.001 0.004 0.000 0.911 0.953

Significance *** ** *** ** NS NS NS

Cane no. P-value <0.001 0.001 0.019 0.029 0.000 0.198 0.857

Significance *** *** * * NS NS NS

Cane mass (g) P-value <0.001 <0.001 <0.001 0.004 0.086 0.661 0.982

Significance *** *** *** ** NS NS NS

Pred. fruitfulness P-value 0.953 0.001 0.232 0.216 0.079 0.136 0.456

Significance NS *** NS NS NS NS NS

Actual fruitfulness P-value <0.001 0.544 0.003 0.141 0.001 0.143 0.881

Significance *** NS ** NS *** NS NS

PBN (%) P-value 0.606 0.017 0.043 0.919 0.004 0.546 0.328

Significance NS * * NS ** NS NS

Flower no. P-value <0.001 0.244 <0.001 0.058 0.033 0.139 0.787

Significance *** NS *** NS * NS NS

Seeded berries P-value <0.001 0.011 0.025 0.026 0.293 0.019 0.204

Significance *** * * * NS * NS

Seedless berries P-value 0.004 0.280 <0.001 0.33 <0.001 0.283 0.423

Significance ** NS *** NS *** NS NS

LGOs P-value 0.608 0.348 <0.001 0.117 0.04 0.711 0.113

Significance NS NS *** NS * NS NS

Fruitset (%) P-value <0.001 0.056 <0.001 0.001 <0.001 0.744 0.428

Significance *** NS *** *** *** NS NS

Total berry no. P-value <0.001 0.008 0.795 0.181 0.148 0.080 0.334

Significance *** ** NS NS NS NS NS

CI P-value <0.001 0.042 <0.001 0.000 0.000 0.639 0.253

Significance *** * *** NS NS NS NS

MI P-value <0.001 0.189 <0.001 0.149 <0.001 0.019 0.342

Significance *** NS *** NS *** * NS

Berry mass (g) P-value 0.000 0.344 0.272 0.059 0.583 0.539 0.820

Significance NS NS NS NS NS NS NS

Bunch mass (g) P-value <0.001 0.002 0.017 0.039 0.120 0.870 0.322

Significance *** ** * * NS NS NS

Yield (kg/m canopy) P-value <0.001 0.026 <.001 0.003 <0.001 0.392 0.909

Significance *** * *** ** *** NS NS

FM/PM ratio P-value <0.001 0.681† 0.006 0.137 <0.001 0.502 0.314

Significance *** NS ** NS *** NS NS

ANOVA of cultivar, rootstock and season effects and cultivar x rootstock, season x cultivar, season x rootstock and season x cultivar x rootstock interactions. Thecomparison of both cultivars on treatments over three seasons is given by P < 0.05(*), P < 0.01(**), P < 0.001(***) and not significant (ns). For all cultivars, treatmentsand seasons, each value represents the mean of five replicate samples for each group. †(FM: PM), Fruit mass: Pruning mass ratio and is the yield divided by the pruningmass per metre of cordon. CI, Coulure Index; LGOs, live green ovaries; MI, Millerandage; PBN, primary bud necrosis.



Therefore, it is more probable that the prolonged floweringperiod for both cultivars coupled with climatic conditions con-tributed to the decrease in fruitset during the flowering periodof 2011, although, further studies on flower number and func-tionality are warranted.

Effect of rootstocks on fruitfulnessRootstocks can affect fruitfulness through changes inscion vigour (Candolfi-Vasconcelos et al. 2009). Ramsey, 1103Paulsen and Schwarzmann have previously been shown toincrease yield of the grafted scion through an increase in fruit-fulness (Hedberg et al. 1986, Sommer et al. 2000, Keller et al.2001, Stevens et al. 2008). Fruitfulness for Ramsey has alsobeen described as poor when compared to that of Sultana onown roots due to a higher vegetative growth of Sultana graftedto Ramsey (Sommer et al. 2001). In the present study, bothMerlot and Cabernet Sauvignon on Ramsey and 1103 Paulsenhad a higher fruitfulness than that of ungrafted vines, whileCabernet Sauvignon grafted to Schwarzmann had a significantlyhigher fruitfulness than this cultivar grafted to all other root-stocks, and this resulted in a significantly higher yield. Thedifference in fruitfulness for scions on Ramsey between thestudy of Sommer et al. (2001) and the present study may bepartly due to the different vigour potentials of the scion—highfor Sultana, moderate for Cabernet Sauvignon and low forMerlot (Dry 2007). Although vegetative growth (as measuredby pruning mass and cane number) was higher on Ramsey thanthe ungrafted for both scion cultivars, this was not to the extentwhereby higher shoot vigour or denser canopies were observedas described in Sommer et al. (2001). Conversely, a reducedfruitfulness was observed when both cultivars were grafted to

5C Teleki. In particular, both potential and actual fruitfulnesswere lower when 5C Teleki was used as the rootstock forCabernet Sauvignon. Pruning mass was not significantly higherfor 5C Teleki than for the other rootstocks, but a higher averagecane mass may have contributed to an increased vegetativepotential that consequently lowered fruitfulness.

No significant difference in PBN between treatments wasobserved for Cabernet Sauvignon. Dry et al. (2003) similarlyfound no rootstock effect on PBN for Shiraz. Other studieshave shown site and climate affect the responses of rootstocksto PBN: no effect at one site and a significant effect at theother when rootstocks were compared at two separate loca-tions (Cox et al. 2012). In the present study, the rootstocksignificantly affected the incidence of PBN for Merlot only. Thehighest incidence of PBN was observed for rootstocks 5CTeleki and 1103 Paulsen in 2010. Incidence of PBN greaterthan 20% in a vineyard is considered to have a significantimpact on fruitfulness and therefore final yield (Pool 2000).Both cultivars had, in general, a low level of PBN. Forexample, the incidence of PBN in Cabernet Sauvignon wasbetween 9 and 19% and 7 and 16% for Merlot across theanalysis. The incidence of PBN has previously been associatedwith high shoot vigour (Lavee et al. 1981, Dry and Coombe1994) and canopy shading (May 1965, Perez and Kliewer1990, Wolf and Warren 1995). An indication of vegetativegrowth may be deduced at pruning time through pruningmass and its components, cane mass and cane number (Smartand Robinson 1991). Ideally, pruning mass should be 0.3 to1.0 kg/m cordon (Shaulis and Smart 1974, Kliewer andDookoozlian 2001, Smart 2001) and cane mass 25 to 45 g(Reynolds 2001, Smart 2001). Based on these studies, it is

1103 Paulsen

5C Teleki

Ungra�ed

RamseySchwarzmann

1103 Paulsen

5C Teleki

Ungra�ed

RamseySchwarzmann

Seeded

Fruit set

CI

MI

Bunch mass

YieldPruning mass

Cane number

Cane mass

-4

-3

-2

-1

0

1

2

3

4

-4 -3 -2 -1 0 1 2 3 4

PC2

(10.

78 %

)

PC1 (79.59 %)

Biplot (axes PC1 and PC2: 90.38 %)

Figure 2. Principal component analysis of reproductive performance and vegetative growth variables for Cabernet Sauvignon ( ) and Merlot( ) on ungrafted (control) and grafted to Ramsey, 5C Teleki, Schwarzmann and 1103 Paulsen rootstocks.



apparent that neither Cabernet Sauvignon nor Merlot hadexcessive vegetative growth to a cause high incidence of PBN.

Effect of rootstock on reproductive performanceNo significant changes to fruitset were observed for CabernetSauvignon in our study, however, the level of fruitset forCabernet Sauvignon was low (average 24%), and the seasonhad a greater influence on fruitset than rootstock type. In con-trast, Merlot grafted to rootstocks had significantly higherfruitset and bunch parameters than that of ungrafted Merlot.Fruitset was 41 to 75% higher for Merlot grafted to rootstocks.Fruitset was highest for 5C Teleki, followed by 1103 Paulsen,Schwarzmann and Ramsey. The increased fruitset of Merlotgrafted to rootstocks resulted in a significantly higher number ofberries per bunch and a greater number of seeded berries. Arelationship between seed content and berry size has previouslybeen reported (May 2000, Friend et al. 2009), and althoughseed number per berry was not measured in the present study,it was observed that rootstock treatments with a higher bunchmass had more seeded berries (R2 = 0.633).

Merlot ungrafted and grafted to 1103 Paulsen had a highermeasure of MI than grafted to Schwarzmann and Ramsey. Pre-vious studies have identified that cultivar differences contributeto MI and CI (Dry et al. 2010) and that management practicessuch as shoot topping can decrease the degree of these disorders(Collins and Dry 2009). It is also apparent some rootstocks(Ramsey and Schwarzmann) may have a negative influence onthe expression of MI (i.e. decrease the incidence) for Merlot butnot for Cabernet Sauvignon.

The cultivars Cabernet Sauvignon and Merlot wereselected for this study as they are commonly regarded assusceptible to poor fruitset due to a high incidence of bothmillerandage and coulure, along with lower documentedyields than cultivars such as Chardonnay or Sangiovese (May2004, Dry et al. 2010). Furthermore, both scions have beenshown to be responsive to rootstocks (Zapata et al. 2001,2004, Tandonnet et al. 2010). In the current study, reproduc-tive performance differed between the two cultivars: CabernetSauvignon (24%) had a lower fruitset than Merlot (44%) overthe 3-year period. Ungrafted Merlot is regarded as having poorfruitset at 31% (Dry et al. 2010). An average fruitset of 30%was reported for ungrafted Merlot which supports the findingsof Dry et al. (2010).

In this study, reproductive development for Merlot wasable to respond more favourably to rootstocks than CabernetSauvignon. Previous studies have identified the reliance ofMerlot on reserve carbohydrates for nutrient supply to thedeveloping inflorescence at flowering, whereas other cultivarssuch as Pinot Noir sequester nutrients from photosynthesis(Zapata et al. 2004).

Sugars provide the main energy source for reproduction anda reduction in sugars has been shown to lead to disorders suchas bud necrosis (Vasudevan et al. 1998) and coulure (Lebonet al. 2008).The reliance of Merlot inflorescences on reservecarbohydrates has been previously suggested (Zapata et al.2004). These authors found a requirement on root reserves forMerlot until E–L 31 (pea size berries), whereas autotrophy inPinot Noir occurred prior to E–L 27 (fruitset). These differenceswere shown to increase susceptibility of Merlot to coulure whenthe level of remobilisation of carbohydrates and nutrients wasdeficient (Zapata et al. 2004).

For Merlot, grafting to a rootstock increased both vegetativegrowth and yield. It is likely that root density and root distri-bution differed between the grafted and ungrafted vines, and

this may have lead to the observed increase in reproductivedevelopment. Previously, rootstock genotype has been shown toaffect root density, root distribution, nutrient status and starchconcentration (Swanpoel and Southey 1989, Keller et al. 2001,Dry 2007, Cox et al. 2012), and rootstocks with a higher rootdensity have been shown to have higher vegetative mass andyield per vine (Swanpoel and Southey 1989). The observedreduction in coulure and increase in fruitset for Merlot vinesgrafted to rootstocks is likely to be due to an improvedremobilisation of reserve carbohydrates attributed to the root-stock root system. While we did not measure reserve carbo-hydrates in the vines, evidence for a reliance on reserve carbo-hydrates for Merlot has previously been documented (Zapataet al. 2004).

This study observed that grafting Merlot to a rootstockincreased fruit set and bunch mass and decreased CI. Furtherexamination of grafted vine data showed that Merlot onSchwarzmann, 1103 Paulsen and 5C Teleki had more seededberries and total berries per bunch than that of ungrafted vines.In addition, Merlot on 1103 Paulsen, Schwarzmann andRamsey had higher actual fruitfulness and yield than that ofMerlot ungrafted and on 5C Teleki. A high yield from Ramseyand 1103 Paulsen has been reported previously for Chardonnayas a scion (Stevens et al. 2008).

ConclusionThe reproductive performance of Cabernet Sauvignon andMerlot scions was affected when grafted to rootstocks. The com-parison of the same rootstocks with the two cultivars at thesame site, coupled with the indices for fruitset, enabled a thor-ough examination of rootstock effects on various components ofreproduction. This study highlights the cultivar-specific interac-tions that occur for individual rootstocks and as a result, iden-tified that cultivars can differ in their reproductive performancewhen grafted to the same rootstock. For Cabernet Sauvignon,reproductive performance was affected by rootstock treatmentsthrough increased fruitfulness. For Merlot, a combination offruitfulness and fruitset effects by rootstock increased yield com-pared to that of ungrafted vines. In summary, fruitset wasincreased in Merlot for all rootstock treatments relative to thatof ungrafted vines. This corresponded to an increase in berrynumber per bunch and proportion of seeded berries within thebunch.

Further work to classify reproductive performance of root-stocks over a wider climatic and cultivar spectrum will benefitour knowledge of rootstocks in relation to fruitset. The use ofrootstocks on cultivars considered to be susceptible to poorfruitset would be beneficial at Wrattonbully and other coolregions where poor fruitset occurs.

AcknowledgementsThis project was funded by Australia’s grapegrowers throughtheir investment body, the Grape and Wine Research and Devel-opment Corporation along with The Phylloxera and GrapeIndustry Board of South Australia. Thanks to Teresa Fowlesand to the staff at Waite Analytical Services, Glen Osmond, SA,Australia for their help with ICP-OES and also to ScholefieldRobinson Horticultural Services, Parkside, SA, Australia fortheir assistance with bud dissections. Special thanks go toYalumba Wine Company for the use of their vineyard atWrattonbully and to James Freckleton, Daniel Newson, WendySmith and John Kenny for their valued assistance throughoutthe trial.



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http://www.phylloxera.com.au/resources/sa-winegrape-crush-survey/

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http://www.nysaes.cornell.edu/hort/faculty/pool/budcoldinjury/Assessingbudcoldinjury.html

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Manuscript received: 16 August 2012

Revised manuscript received: 8 January 2013

Accepted: 13 May 2013

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.12032/abstract

Table S1. Effect of rootstock and season on reproductive per-formance for Cabernet Sauvignon grown in Wrattonbully in2009, 2010 and 2011 seasons.



http://onlinelibrary.wiley.com/doi/10.1111/ajgw.12032/abstract

http://onlinelibrary.wiley.com/doi/10.1111/ajgw.12032/abstract

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