Abstract:
Differences in petiole K+ concentration of ungrafted grapevine rootstocks grown under field conditions at Merbein, Victoria, were compared with the rootstock effects on grape juice pH of the scion varieties Chardonnay and Ruby Cabernet. Significant positive correlations were obtained between grape juice pH of the scion varieties on various rootstocks and K+ accumulation in the petioles of ungrafted rootstock vines. Rootstock varieties that contributed to high pH in the grape juice of the scion (e.g. Freedom, Dog Ridge, Rupestris du Lot) showed high K+ concentrations in their petioles, while those rootstocks that contributed to low pH in the grape juice of the scion (e.g. 140 Ruggeri, 1202 Couderc, 110 Richter), had low K+ concentrations in their petioles. In 2 water culture experiments in the glasshouse, K+ uptake and distribution in ungrafted rootstock vines was examined at different K+ levels. In the first experiment the rootstocks 140 Ruggeri and Freedom had similar K+ concentrations in the various plant parts when grown in nutrient solution with 0.1 mmol K+/L. With K+ concentrations of 1, 2, and 10 mmol/L in the nutrient solution Freedom had significantly higher K+ contents in leaves and petioles than 140 Ruggeri. When K+ supply was increased from 1 to 2 mmol/L, K+ concentrations in the various plant parts were not significantly increased. However, when the supply was increased to 10 mmol/L, K t concentrations were significantly different. In the second experiment with K+ levels of 1 and 10 mmol/L, higher K+ contents were obtained in the basal and apical leaves of Dog Ridge and Ramsey compared with 140 Ruggeri, Schwarzmann, 1103 Paulsen and Sultana, while in roots, 140 Ruggeri, 110 Richter and Sultana had the highest K+ contents. Dog Ridge and Rarnsey are both known to increase scion grape juice K+ concentration and pH of the scion variety, while 140 Ruggeri and 1103 Paulsen contribute to low grape juice K+ concentration and pH. The results demonstrate that differences between rootstocks in the extent of K+ accumulation in the shoot are a major determinant of the rootstock effects on grape juice pH. The extent of K+ accumulation can best be measured in basal leaves or petioles. This provides a screening method for the evaluation of rootstocks which restrict K+ accumulation and contribute to lower grape juice pH.