grapegrowing 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. ROOTSTOCK VIGOUR, VINE PERFORMANCE AND BERRY TRAITS In a field trial involving seven scions (Gamay, Chasselas, 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 vigour was obtained which was conferred primarily through the rootstock. This enabled correlations to be tested between variables. Grape juice K concentration was positively correlated with pruning wood weight (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 negatively 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 correlated with pruning wood weight (r=0.57, P<0.001) and juice K (r=0.69, P<0.001). In a second field study involving Shiraz grafted to five standard rootstocks (Freedom, Ramsey, 1103 Paulsen, 140 Ruggeri and Dogridge) and to 55 hybrid rootstocks from the CSIRO rootstock breeding program, a similar wide range in vine vigour was obtained which 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 with berry K concentration (r=0.93, P<0.001), pruning wood weight (r=0.70, P<0.001) and berry weight (r=0.55, 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 vigour selections demonstrating lower grape juice K accumulation in Sunraysia (Victoria) trials have progressed to release in Australia with Plant Breeders Rights protection (Walker and Clingeleffer 2009; Clingeleffer et al. 2011). 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 Koorlong 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 irrigation water electrical conductivity was different between the sites, ranging from 0.4 dS/m at one site to 3.3 dS/m at another site. Soil K concentrations also varied from site to site (Walker and Blackmore 2012). 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 48 Grapegrower & Winemaker in both grape juice and wine (Walker and Blackmore 2012). It was clear from the data that as grape juice and wine K increase, [H+] decreases and pH increases. The relationship is linear for Chardonnay and exponential for Shiraz for both grape juice and wine (Walker and Blackmore 2012). It was also clear from this work that certain rootstocks can result in higher K in wine produced from the different sites. For example, rootstock K 51-40 resulted in highest wine K concentrations at the Merbein Chardonnay and Shiraz sites and also at the Nuriootpa Chardonnay and Rowland Flat Shiraz sites in the Barossa Valley (Walker and Blackmore 2012). However, at other sites, e.g. 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 grapes on own roots, or grafted to Ramsey, 1103 Paulsen, 140 Ruggeri and 101-14 rootstocks, positive linear relationships (R2=0.9) were obtained between grape juice K concentration and grape juice total soluble solids (Walker et al. 2000). Furthermore, the slope of the relationships was the same at both sites, despite large differences in electrical conductivity of the irrigation water, specifically 0.4 dS/m at one site (Koorlong) and 2.1 dS/m at the other site (Merbein). Similarly, using data for grape juice K and total soluble solids obtained at harvest for each of Chardonnay and Shiraz in trials at four sites involving vines on own roots or grafted to eight different rootstocks, strong positive correlations (R2=0.7) were obtained between the variables (Walker and Blackmore 2012). Both sucrose and K are transported in the phloem to developing berries (Lang and Thorpe 1989). This close association between the variables is further evidence of a potential relationship during phloem loading and unloading. WINE COLOUR HUE IS POSITIVELY CORRELATED WITH WINE PH. The strong correlation between K and pH in grape juice and wine has already been noted. As previously reported by Somers (1977), high wine pH has a negative impact on wine colour. Using Shiraz wine data from the trial involving four sites, where wine was made using fruit from own rooted vines and fruit from Shiraz grafted to five different rootstocks, wine colour hue was positively correlated with wine pH (Walker and Blackmore 2012). Lower colour hue means a brighter wine, hence the higher colour hue with higher wine pH means less brighter wines. Similar observations were made by Gong et al. (2010). DISTRIBUTION OF K IN GRAPE BERRIES When examined in terms of total berry K content, the percentage of total berry K in skins is similar to the percentage of total berry K in pulp, with only a small percentage of total berry K in seeds. For example, for the grape varieties Muscat Gordo Blanco, Shiraz, Riesling, Cabernet Sauvignon and Chardonnay, all growing on their own roots, the mean percentage of total berry K content in skin, pulp and seed was 43%, 50% and 7%, respectively (Walker et al. 1998). For each of the varieties grafted on Ramsey, the mean percentage of total berry K content in skin, pulp and seed was 41.5%, 53% and 5.5%, respectively (Walker et al. 1998). On a concentration basis, because skins are only small percentage of total berry weight, K concentrations are much higher in berry skins than in pulp. For example, skin K concentrations were 4.0 – 4.5 fold higher www.winetitles.com.au March 2016 – Issue 626