Leaf Removal Accelerated Accumulation of Delphinidin-based Anthocyanins in ‘Muscat Bailey A’ [Vitis × labruscana (Bailey) and Vitis vinifera (Muscat Hamburg)] Grape Skin

Removing leaves around the grape cluster of Muscat Bailey A [Vitis × labruscana (Bailey) and Vitis vinifera (Muscat Hamburg)] cultivated in pergola style at the start of veraison increased the photosynthetically active radiation value by more than approximately 60and 30-fold compared with those of the control and grape cluster from vines grown on ground covered with reflective film (reflective-film-treated grape cluster), respectively. The improved light exposure caused by leaf removal increased total anthocyanin concentration and changed the ratios of anthocyanin derivatives in the grape skins. Total anthocyanin concentration in the leaf-removal-treated grape skins 10 weeks after veraison increased by approximately 6.5-fold compared with that of the control. In addition, delphinidin-based anthocyanin concentrations in the leaf-removal-treated grape skins increased by approximately 7-fold compared with those of the control. Leaf removal up-regulated anthocyanin-synthesis-related genes in grape skins, such as CHS, F3′H, F3′,5′H, and UFGT. In particular, the overexpression of F3′,5′H in the leaf-removal-treated grape skins suggested that leaf removal contributed to the accumulation of delphinidin-based anthocyanins in grape skin. These findings are expected to improve viticultural practices with the aim of producing dark-colored red wine made from cultivars grown in pergola style.