Defoliation at berry set alters grape composition and gene expression during berry development in two Greek Vitis vinifera L. cultivars

The quality traits of a given grapevine cultivar are determined by the combinatorial action of the genotype, and environmental factors such as soil, landscape, and climate. Nonetheless, another critical factor is vineyard management. The forthcoming effects of climate change on viticulture represent a challenge for the application of sustainable practices. The impact of leaf removal at berry set stage on the Greek Vitis vinifera L. cultivars 'Agiorgitiko' and 'Assyrtiko' (a red- and white-berry cultivar, respectively) was investigated during the 2019 and 2020 vintages. Vine physiology measurements and berry sampling were performed at three phenological stages: green berry, veraison and harvest. Grape berry composition and the expression level of specific genes were analysed during ripening. Defoliation decreased berry weight in Assyrtiko, while no significant effect was observed in Agiorgitiko. The treatment resulted in a significant increase in total soluble solids and reduced acidity compared to the controls in both cultivars, while the effect on total phenols mainly depended on climate conditions. The expression profile of the genes examined was also altered during ripening, whereas the response to defoliation mainly depended on the vintage and the cultivar. Taken together, the results suggest that defoliation is a useful technique for maintaining grape and wine quality.