Vitis 49 (3), 101–106 (2010) Sugar accumulation in 'Zweigelt ' grapes as affected by "Traubenwelke"

a physiological disorder during berry ripening, is a severe threat to grape production in numerous wine-growing 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 symp-toms were detectable, and subsequently the degree of ripeness remained unchanged until harvest. The results suggested that development of "Traubenwelke " initiat-ed 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 occur-rence. The gas exchange of leaves positioned opposite to healthy clusters was not significantly different than that of leaves opposite to unhealthy clusters. K e y w o r d s: 'Zweigelt', Traubenwelke, grape wilting, berry shrivel, sugar accumulation, photosynthesis