Effects of post-flowering leaf removal on the phenolic composition of three red Vitis vinifera L. cultivars under semiarid conditions

Among seasonal practices that affect grape quality, selective leaf removal at the cluster zone is accepted as a powerful technique to manipulate flavonoid content of grapes and wines. However, most of research on fruit-zone defoliation has been conducted under temperate climate and it remains uncertain if cluster exposure would be a recommendable practice in semiarid viticultural areas. In this study, we investigated, over two consecutive seasons, the effect of the severity of post-flowering leaf removal on the growth and phenolic composition of berry skin and seeds in three Vitis vinifera L. genotypes (Merlot, Cabernet Sauvignon and Sangiovese) under the semiarid conditions of Northern Greece. Three different severities of leaf removal in the fruit-zone were applied manually at berry set: non defoliated (ND), removal of the lateral shoots of the first six basal nodes (LR) and full removal of the total leaf area (main leaves and lateral shoots) of the first six basal nodes (FR). Grape samples were obtained at commercial harvest. Leaf removal decreased yield per vine and cluster weight in Merlot and Sangiovese but berry fresh weight was unaffected in both cultivars. On the contrary, in Cabernet Sauvignon yield was unaffected but berry size was reduced by leaf removal. Fruit zone leaf removal did not affect must soluble solids and increased titratable acidity only in Merlot. Defoliation increased skin anthocyanins in Merlot and Cabernet Sauvignon but significantly reduced seed flavan-3-ols mainly as a result of the reduction in catechin and epicatechin amount. However, leaf removal had limited effect in Sangiovese phenolic profile.