The Effect of Irrigation Amounts during Fruit Ripening on Skin Anthocyanins in Forced Cabernet Sauvignon Grapevines

Grapevines can be forced to regrow so fruit ripening can be shifted to the cooler portion of the growing season while enhancing fruit quality for wine making, including significantly higher content of skin anthocyanins. In order to determine if irrigation management can further increase skin anthocyanins in forced fruit, a study was conducted in 2013 and 2014 with mature Cabernet Sauvignon grapevines on Freedom in Fresno, CA, a warmer region for wine grape production. Vines were forced in mid-June by hedging primary shoots to six nodes and removing all clusters, leaves, and summer laterals. The forced vines were irrigated at 100% crop evapotranspiration (ET_C) until veraison, and then at 40%, 60%, 80%, or 100% ETc in a completely randomized block experiment. Berries were sampled randomly from fruiting zone at commercial maturation of 24 to 26 °Brix, while their skins were analyzed for individual anthocyanins, using a HPLC system. Fifteen individual anthocyanins were detected, including non-acylated, acetylated, and p-coumaroylated glucosides of delphinidin, cyanidin, petunidin, peonidin, and malvidin aglycones. Tri-hydroxylated anthocyanins accounted for more than 85% of the total skin anthocyanins, and more than half of the trihydroxylated anthocyanins were malvidin-based. Total skin anthocyanins, acylated anthocyanins, and tri-hydroxylated anthocyanins were significantly higher, by approximately 15 to 35%, in vines irrigated at 40 and 60% ETc than those at 80 and 100% ETc. The concentration of malvidin-based anthocyanins, especially malvidin-3-glucoside and malvidin-3-acetyl-glucoside, was also higher when vines were irrigated with less water. However, irrigation amounts did not affect either skin content of p-coumaroylated anthocyanins or proportion of each individual anthocyanins. The study demonstrated that post-veraison reduction in irrigation amounts can increase skin anthocyanins, primarily the trihydroxylated and malvidin-based anthocyanins, in forced grapevines to further enhance fruit quality.