Effect of two exogenous plant growth regulators on the color and quality parameters of seedless table grape berries

Some red-pink table grape varieties, cultivated in warm climates, can fail in achieving the right level of anthocyanins responsible for the intense and uniform red color of berries. Nowadays, this is becoming an important technological issue in the Mediterranean area, which may result in decreasing market acceptance and potential economic value of table grape. Usually, plant growth regulators or phytohormones, such as S-ABA, can overcome this problem because they drive the accumulation of anthocyanins over the ripening season. Harpin proteins (HrP), which enhance the plant disease resistance, may be supposed to stimulate the anthocyanins biosynthesis in grape skin if applied close to veraison. Therefore, this research aimed at comparing the effect of HrP and S-ABA over the anthocyanin and color improvement of Crimson Seedless table grape grown in Southern Italy. For the first time, the exogenous treatment with HrP showed as effective as the less sustainable S-ABA one in favoring the anthocyanin accumulation, leading to peonidin-3-O-glucoside, cyanidin-3-O-glucoside, and malvidin-3-O-glucoside values up to 4 folds higher than control grapes and giving rise to a greater concentration of the more stable acylated anthocyanins. Overall, the color of berries was improved but keeping high the other quality characteristics.