Viticultural techniques of canopy management to mitigate the effects of global warming

Résumé

The overall aim of this thesis was to assess the effects of different cultural techniques on grape yield components and fruit quality. In particular, within the climate change scenario, their effectiveness of delaying grape technological ripening and improving the anthocyanins-to-sugar ratio was the main priority of the research. All the trials were conducted under field conditions. The three main cultural techniques were: severe shoot trimming (SST) after berry set, minimal pruning (MP) and late winter pruning (LWP). In addition, basal leaf removal (LR), a wildly used cultural technique, was also studied in order to evaluate the impacts on grape and wine characteristics. The results show that SST could delay grape ripening by two to three weeks, however, under conditions of low vigor, grapes were not able to mature properly with extremely severe trimming (trimming twice). In spite of the relatively cooler ripening period, the anthocyanin accumulation was not enhanced significantly. Nonetheless, SST sometimes reduced the berry size thus increasing the skin-to-pulp ratio, in this way, juice anthocyanin concentration was increased. SST helped to improve organic acid composition by increasing the tartaric acid and reducing the malic acid. The experiment on MP demonstrated clearer results in the size of the berry: the significantly smaller berries contributed to the darker color of MP juice, but the ability of berry skin to synthesize anthocyanins was not improved by the ripening delay. LWP at stage G (LWPG) and H (LWPH) delayed berry ripening to a larger extent and created much cooler ripening conditions than normal winter pruning. However, this achievement was at the cost of a considerable yield loss and only LWPH succeeded to improve the anthocyanins-to-sugars ratio of grape juice. LWP before or during stage F did not affect yield components nor fruit composition. The full exposure of clusters due to a severe LR after fruit set did not exert any negative effects on grape quality, on the contrary, it also increased the ratio between tartaric acid and malic acid and the results of the sensory evaluation show that LR enhanced wine color and body. Besides, LR reduced the sugar concentration required in the berry for the onset of anthocyanin synthesis.