Water stress affects the flavonoid composition in ‘Cabernet Volos’ skins, with main effects on structural characteristics of proanthocyanidins

Modern viticulture aims to produce high quality wines with low environmental impact, while being hindered by the challenges posed by climate change. This study would contemplate all three of these topics, investigating the modifications of flavonoid composition on berry skins of ‘Cabernet Volos’ (a new grapevine cultivar resistant to fungal diseases), under drought conditions. During the 2018 growing season, a water stress experiment was carried out at the experimental farm of the University of Udine on ‘Cabernet Volos’ grown in field conditions, comparing a well-watered with a non-irrigated treatment. Berry samples were collected from véraison to harvest, skins were removed under liquid nitrogen, extracted in organic solvents and analysed for anthocyanin concentration and structural characteristics of proanthocyanidins (mean degree of polymerization (mDP), % of galloylation (%G), and % of prodelphinidins (%P)). In parallel, the expression of target-related genes was ascertained through qPCR analysis. On the stressed skin samples mDP and %G were tendentially lower and higher, respectively, while significantly higher values were found for %P. With regards to gene expression, GAT genes (putative genes responsible for the galloylation of proanthocyanidins) were upregulated by water stress, and a similar trend were showed also by four F3’5’H homologue genes that well correlate with the higher %P in berry skin proanthocyanidin composition.