Potassium uptake and redistribution in Cabernet Sauvignon and Syrah grape tissues and its relationship with grape quality parameters.

BACKGROUND: The present study investigated the potassium (K) levels in petiole and other grape tissues during ripening in Vitis vinifera Shiraz and Cabernet Sauvignon, grown in areas with differences in vigour, as well as with and without leaf thinning. Potassium levels in petiole, seeds, skin and flesh were related to grape pH, acidity, berry weight and total soluble solids.

RESULTS: Differences in K levels in petiole were in accordance with the differences in soil K. Leaf thinning gave rise to higher K levels in petiole but, in grape tissues, the differences were not significant in all samplings, with greater differences at the end of the growing cycle. Potassium levels per berry in grape tissues increased from veraison to harvest, with K mainly accumulated in skins and, to a lesser extent, in flesh. Potassium levels in flesh positively correlated with pH and total soluble solids, whereas the correlation with titratable acidity was negative.

CONCLUSIONS: Grape juice pH and total soluble solids positively correlated with K, whereas titratable acidity correlated negatively. Leaf thinning increased K levels in petiole, although differences in K levels in grape tissues were not significant. This suggests the need to consider the K berry concentration when aiming to optimise K fertilisation programmes. © 2016 Society of Chemical Industry.