Effects of extra potassium supply and rootstocks indicate links between water, solutes and energy in Shiraz grapevines (Vitis vinifera) pericarps

Potassium (K) is essential for the development of grapevines (Vitis vinifera), accumulating into berries during maturation. Elevated K has been associated with high sugar and low acidity in juice. Characterising the accumulation patterns of K and other components in pericarps treated with various experimental factors may indicate potential regulators of berry K levels. A soil fertiliser trial using nutrient solutions with two K supply rates was conducted on potted Shiraz vines during berry ripening. Doubled-K supply increased L-malic acid content in the early-ripening phase, and increased K and magnesium concentrations in the late-ripening phase. Doubled-K supply reduced the ratio of K to sodium in later ripening phases, suggesting that the accumulation of K relative to sodium was limited in more mature berries supplied with extra K. Pericarp water percentage, sugar, K and ATP were correlated in both treatments, indicating links between hydration, solute transport and energy in maturing berries. In a separate rootstock trial over the two growing seasons, Shiraz scions grafted onto 420-A rootstock produced berries with lower K concentration and content than those grafted onto Ramsey or Ruggeri-140 rootstocks and own-rooted vines. This study demonstrated that the K supply and berry ripening phase impacted the berry K level.