Sugar accumulation in 'Zweigelt' grapes as affected by "Traubenwelke"

"Traubenwelke" (berry shrivel, grape wilting), a physiological disorder during berry ripening, is a severe threat to grape production in numerous winegrowing areas worldwide. Investigations in Austrian viticulture, focusing on the particularly sensitive grape cultivar 'Blauer Zweigelt' (Vitis vinifera L.), showed that afflicted clusters exhibited insufficient colouring, loss of turgor, low sugar content and high acidity. The aim of this study was to determine the chronological disease development on the basis of the process of sugar accumulation in both unhealthy and healthy clusters in relation to the emergence of visual symptoms. Sugar accumulation in afflicted clusters stopped shortly after veraison, well (approx. 20 days) before visible symptoms were detectable, and subsequently the degree of ripeness remained unchanged until harvest. The results suggested that development of "Traubenwelke" initiated before veraison. Distal clusters were more frequently affected than proximal clusters, whereas the position of the shoot on the vine did not impact frequency of occurrence. The gas exchange of leaves positioned opposite to healthy clusters was not significantly different than that of leaves opposite to unhealthy clusters.