Effects of different water regimes on berry metabolism and composition of 'Aleatico' grapevine

This work reports the results of a trial carried out on 'Aleatico' grapevine, a cultivar cultivated along Tuscany coasts and in Elba Island, from which a typical dessert wine is produced after partial postharvest dehydration of berries. Two different water regimes were applied in the vineyard: not irrigated (water stress, WS) and partially irrigated (moderate water deficit, MWD). WS conditions determined a decrease of stem water potential (SWP) that reached values lower than - 1.4 Mpa, whereas in MWD these SWP levels were registered only for short periods. Significant differences in stomata conductance and net photosynthetic rate values were observed between the two treatments. At harvest, berry weight was reduced of about 20% in WS plants. An effect of similar magnitude was detected for skin weight, while seed weight was not affected. The sugar accumulation process was more pronounced in WS berries and this was paralleled by higher titratable acidity values both at veraison and harvest. Skin anthocyanin content was determined in laboratory and by a fluorimetric method, using the optical sensor Multiplex®2, an innovative portable instrument based on chlorophyll fluorescence, that nondestructively analyzes the berries in the field, under natural light. WS induced a significant increase of anthocyanin biosynthesis as their content resulted to be higher than that of MWD samples. The cultivar 'Aleatico' appeared to be quite tolerant to water stress conditions and this information could be useful also for setting up targeted postharvest dehydration strategies to produce dessert wines. An additional interesting result is represented by the validation of the use of a portable nondestructive instrument to measure skin anthocyanin content directly in the vineyard.