Issue link: http://winesandvines.uberflip.com/i/742839
96 WINES&VINES November 2016 GRAPEGROWING PRACTICAL WINERY & VINEYARD Rootstock vigor, vine performance and berry traits In a field trial with seven scions (Gamay, Chas- selas, Ehrenfelser, Reichensteiner, Egiodola, Perdea and Rousanne) grown on their own roots and on five different rootstocks (SO4, Schwarzmann, 1103 Paulsen, Ramsey and Dogridge), a wide range in vine vigor was observed that was conferred primarily through the rootstock. This enabled correlations to be tested between variables. Grape juice K concentration was positively c o r r e l a t e d w i t h p r u n i n g w o o d w e i g h t (r=0.55, P<0.001), and grape juice pH was positively correlated with juice K (r=0.77, P<0.001). Grape juice tartaric acid was nega- tively correlated with yield (r=0.62, P<0.001) and berry weight (r=0.56, P<0.001), while grape juice malic acid was positively corre- lated with pruning wood weight (r=0.57, P<0.001) and juice K (r=0.69, P<0.001). In a second field study with Shiraz grafted to five rootstocks (Freedom, Ramsey, 1103 Paulsen, 140 Ruggeri and Dogridge) and to 55 hybrid rootstocks from the Commonwealth Scientific and Industrial Research Organization (CSIRO) rootstock-breeding program, a similar wide range in vine vigor was obtained that was conferred primarily by rootstock genotype. In this case, based on three season means for the respective variables, positive correlations were obtained between grape berry K concentration and pruning wood weight (r=0.81, P<0.001). Grape juice pH was positively correlated w i t h b e r r y K c o n c e n t r a t i o n ( r = 0 . 9 3 , P<0.001), pruning wood weight (r=0.70, P < 0 . 0 0 1 ) a n d b e r r y w e i g h t ( r = 0 . 5 5 , P<0.001). Grape juice titratable acidity was positively correlated with pruning wood weight (r=0.85), yield (r=0.66) and berry weight (r=0.66) (all P<0.001). The CSIRO rootstock breeding program has aimed to select rootstock types with lower K accumulation in order to achieve lower grape juice pH and therefore reduced need for pH adjustment during winemaking. Three low- to medium-vigor selections dem- onstrating lower grape juice K accumulation in Sunraysia (Victoria) trials have progressed to release in Australia with Plant Breeders Rights protection. 1,22 Grape juice and wine K and pH relationships for Chardonnay and Shiraz Four trial sites were established in different wine regions of Australia (Merbein and Koor- long in Victoria; Barossa Valley and Padthaway in South Australia) in the early 1990s. Each involved Chardonnay and Shiraz on their own roots and grafted to eight different rootstocks (Ramsey, 1103 Paulsen, 140 Ruggeri, K 51-40, Schwarzmann, 101-14, Rupestris St. George and 1202C). All were drip irrigated, but irriga- tion water electrical conductivity was different between the sites, ranging from 0.4 decisie- mens per meter at one site to 3.3 decisiemens per meter at another site. Soil K concentrations also varied from site to site. 23 Data for grape juice and wine K and pH for Chardonnay and Shiraz across own-rooted vines and the range of rootstocks confirmed the strong positive correlation between K and pH in both grape juice and wine. 23 It was clear from the data that as grape juice and wine K increase, [H + ] decreases and pH increases. The relationship was linear for Chardonnay and exponential for Shiraz for both grape juice and wine. 23 It was also clear from this work that certain rootstocks can result in higher K in wine pro- duced from different sites. For example, root- stock K 51-40 resulted in the highest wine K concentrations at the Merbein Chardonnay and Shiraz sites and also at the Nuriootpa Chardon- nay and Rowland Flat Shiraz sites in the Barossa Valley. 23 However, at another site in Padthaway, South Australia, K concentration in grape juice of Chardonnay and Shiraz from K 51-40 rootstock was comparable with other rootstocks, indicating rootstock-site interactive effects on grape juice K. Grape juice K is correlated with juice total soluble solids When grape juice K and total soluble solids were measured at regular intervals between post-fruit set and berry maturation at two sites (Merbein and Koorlong, Victoria) for Shiraz A Chardonnay leaf shows potassium deficiency symptoms during the post-fruit set phase of devel- opment on poorly drained clay soils. PHOTO BY: HECTOR BEDOLLA