Kidman et al. Reproductive performance of grafted grapevines 1 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, Australia 3 The Australian Wine Research Institute, Wine Innovation Cluster, Glen Osmond, SA 5064, Australia 4 South Australian Research and Development Institute, Research Road, Nuriootpa, SA 5355, Australia Corresponding author: Dr Cassandra Collins, email [email protected] Abstract Background and Aims: Cabernet Sauvignon and Merlot are Vitis vinifera cultivars known to be susceptible to poor fruitset 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 affect reproductive performance. This study assessed the reproductive performance of Cabernet Sauvignon and Merlot grafted to rootstocks. Methods and Results: Cabernet Sauvignon and Merlot grafted to rootstocks, Ramsey, 5C Teleki, Schwarzmann and 1103 Paulsen, were assessed for reproductive performance over three consecutive growing seasons. This was measured by assessing the following: bud fruitfulness, flower number per inflorescence, fruitset (%), berry number per bunch, coulure index (CI), and millerandage index (MI). Fruitset was higher when grafted to rootstocks compared to that of ungrafted vines which corresponded to a decrease in MI and CI. For Cabernet Sauvignon, there were no observed differences in fruitset, however, fruitfulness and bunch number were higher when grafted to rootstocks compared to ungrafted vines. Conclusion: Rootstocks affect fruitfulness and fruitset in Cabernet Sauvignon and Merlot, however, reproductive performance differs between cultivars when grafted to the same rootstock. Significance of the Study: Rootstocks may be used as a management tool to manipulate the reproductive performance of Cabernet Sauvignon and Merlot in cool climates. Keywords: flower number, fruitfulness, fruitset, reproductive performance, rootstock Introduction traces (May 2004). These seedless berries are smaller in size than The process of reproductive development in grapevines can be seeded berries yet still undergo veraison and ripen normally divided into several sequential stages that occur over two suc- (May 2004). Seedless berries generally account for a low pro- cessive growing seasons. As a consequence, the growth and portion of total berry mass approximately 0.9% in Cabernet success of the crop is dependent on bunch initiation in the Sauvignon and 2% in Chardonnay (Collins and Dry 2009), but previous season, inflorescence development, flowering and in Merlot, seedless berries may account for approximately 10% fruitset and the development of seeds and flesh within a grape of all berries (Longbottom 2007). berry in the current season. Factors affecting these processes In contrast, live green ovaries (LGOs), which are formed may include the cultivar (Longbottom 2007, Dry et al. 2010), after pollination, but without fertilisation, are seedless or may climatic conditions (Buttrose 1969, Dunn and Martin 2000, contain only seed traces, remain small, green and hard and Sommer et al. 2000, 2001), excessive vigour or shading (Dry make up less than 1% of total bunch mass (Friend et al. 2000, Collins et al. 2006) and choice of rootstock through an 2003, Longbottom 2007, Collins and Dry 2009). Therefore, effect on scion vigour (Candolfi-Vasconcelos and Castagnoli the relative proportion of seeded and seedless berries and 1995, Cirami 1999, Whiting 2003, Dry 2007, Candolfi- LGOs on a bunch is indicative of grapevine reproductive Vasconcelos et al. 2009, Keller et al. 2011). performance. There are several ways that reproductive performance can Millerandage and coulure are important reproductive phe- be measured in grapevines. For example, bud fruitfulness can be nomena of fruitset as they can have a negative impact on final estimated prior to budburst by a measure of the number of yield (Dry et al. 2010). Millerandage occurs when flowers inflorescence primordia present in a compound bud (Buttrose develop abnormally into either seedless berries or LGOs (May 1969). Other parameters used to measure reproductive devel- 2004, Collins and Dry 2009). Coulure results when flowers opment include fruitset, millerandage and coulure (Dry et al. fail to develop into a berry or LGO, also defined as excessive 2010). Fruitset is a measure of the number of flowers that shedding of ovaries or young berries (May 2004, Collins and successfully develop into berries. In some instances, berries on Dry 2009). Coulure can result from a deficiency in the concen- an inflorescence may not develop seeds or only develop seed tration of soluble and insoluble sugars and may be caused by a doi: 10.1111/ajgw.12032 © 2013 Australian Society of Viticulture and Oenology Inc. 2 Reproductive performance of grafted grapevines Australian Journal of Grape and Wine Research 2013 disturbance in the concentration of growth regulators (Lebon temperature (MJT) for Wrattonbully is 19.6°C and the degree et al. 2008). To measure the expression of coulure and days (DD) (October–April) is 1421 (Longbottom et al. 2011). millerandage, two indices have been developed: millerandage This is comparable to other cool climate regions, such as the index (MI) and coulure index (CI) (Collins and Dry 2009). For Yarra Valley (MJT 19.3°C, DD 1489) and Coonawarra (19.6°C, both indices, the higher the numerical value, the greater the DD 1396) (Coombe and Dry 1988). The vineyard was planted in incidence of the condition. Poor fruitset can result from varia- 2002 at 1818 vines per hectare, with vine spacing and row tion in temperature, nutrition, growth regulators, carbohydrate spacing at 2 m × 2.75 m, respectively, and was trained to a reserves, cultural practices and water stress (Alexander 1965, bilateral cordon with vertical shoot positioned canopy. All Ebadi et al. 1995, May 2004, Longbottom 2007, Lebon et al. grafted and ungrafted vines were sourced from Yalumba 2008, Collins and Dry 2009, Dry et al. 2010). The classification Nursery, South Australia, Australia. All certified clones (CW44 of wine grapes based on reproductive parameters revealed that and D3V14) and rootstocks were tested for viruses and other certain cultivars were more susceptible to poor fruitset than diseases and have corresponding class and source identification others (Dry et al. 2010). Cabernet Sauvignon and Merlot have as well as batch number for traceability. Prior to grafting using been grouped together as they are both susceptible to poor the Omega graft technique, rootstocks were hot water treated fruitset due to a high incidence of both millerandage and for a period of 30 min at 50°C. All vines were planted on the coulure (May 2004, Longbottom 2007, Dry et al. 2010). same day as potted one-year-old vines, selected from the Propagation of a scion with a rootstock results in a grafted nursery specifically for vine uniformity and size. vine, and ungrafted vines differ from grafted vines due to the The vineyard had an elevation of 83 m. Vines were spur development of the graft union (Tandonnet et al. 2010). The pruned by hand to approximately 40 nodes per vine to match formation of callus tissue and vascular tissue from the grafting the commercial pruning level of the vineyard. Vines were drip process house the newly formed xylem and phloem vessels that irrigated, using an underground water source (bore). Schedul- maintain the flow of solutes between the scion and the root- ing of irrigation was based on Gbug (gypsum block) sensor stock (Nicholas 1992, May 1994). Tandonnet et al. (2010) sug- assessments, and irrigation was approximately 1.4 mL/ha gested that the interaction between the combined scion and (140 mm) each season. Meteorological conditions were moni- rootstock may have a greater effect than the rootstock effect tored using daily temperature and rainfall data sourced from the alone. In some combinations, rootstock genotype has been Bureau of Meteorology weather station at Naracoorte Airport, shown to influence biomass allocation between roots and located approximately 6 km to the west of the trial site. Long- shoots, while in other combinations the scion genotype had an term average temperature, growing degree days (GDD) and influence on shoot development of grafted vines. Tandonnet rainfall data were calculated from weather data archived on et al. (2010) also concluded that root development including the Bureau of Meteorology website (http://www.bom.gov.au/ root length and root system structure of rootstock genotypes is climate/dwo/IDCJDW5044.latest.shtml). strongly influenced by scion genotype. The long-term average rainfall for the region is Reproductive development of grapevines may potentially be 561 mm (http://www.bom.gov.au/climate/dwo/IDCJDW5044. managed through the use of rootstocks (Candolfi-Vasconcelos latest.shtml). The site is located within a phylloxera-free region and Castagnoli 1995, Cirami 1999, Whiting 2003, May 2004, that allows for the planting of ungrafted V. vinifera vines. The soil Dry 2007). For example, fruitfulness of the scion has been found is a mixture of loamy sand over red clay on calcrete; medium to increase or decrease depending on the rootstock to which thickness loamy sand over a well structured red clay on calcrete, the scion was grafted (Hedberg et al. 1986, Sommer et al. 2000, with areas of exposed red clay on calcrete (Longbottom et al. 2001, Keller et al. 2001, 2011, Stevens et al. 2008, Candolfi- 2011). Vasconcelos et al. 2009). An attempt to classify rootstocks according to their fruitset potential has been previously reported Experimental design by several authors (Candolfi-Vasconcelos and Castagnoli 1995, Vitis vinifera L. cultivars Merlot (clone D3V14) and Cabernet Cirami 1999, Whiting 2003, May 2004, Dry 2007, Keller et al. Sauvignon (clone CW44) were grafted to four American Vitis 2011).