Physical, Biochemical and Phytochemical Quality Variations in Grapes Treated by Exogenous Application of Gibberellic Acid

Gibberellic acid (GA(3)) application may help in attaining good bunch architecture of grapes. The current study was aimed to find the right stage and dose of GA(3) to attain the desired level of compactness in grapes and its impact on fruit physical and biochemical quality. Exogenous application of GA(3) was carried out on 'Sultanina-C', 'Flame Seedless' and 'NARC Black' cultivars of table grapes either at pre-bloom or full bloom stage at 5, 10, 20 and 30 ppm during first year experiment, while plain water was applied in control. The best treatments were repeated during the second year experiment. Medium loose bunches were obtained where 10 ppm GA(3) was applied especially at the pre-bloom stage in all cultivars. Pre-bloom application of GA(3) significantly increased the bunch length of 'Sultanina-C' and 'Flame Seedless'. Variations in total soluble solids (TSS) were recorded during the years and cultivars, ranging from 14.4 to 20 degrees Brix. Pre-bloom application of GA(3) (10 ppm) significantly increased the TSS of 'Sultanina-C' and 'Flame Seedless' during both years, but 'NARC Black' showed a significant increase only in the first year. Vitamin C, total phenolic contents (TPC) and antioxidant scavenging activity (ASA) were decreased with the application of GA(3). Primary antioxidant enzymes including superoxide dismutase (SOD) and catalase (CAT) were reduced in response to treatments, while peroxidase (POX) and polyphenol oxidase (PPO) followed a reverse trend. In conclusion, 10 ppm GA(3) at the pre-bloom stage can help in obtaining medium loose bunches in 'Sultanina-C' and 'Flame Seedless' that trigger maturity by increasing TSS, but bioactive compounds and the level of primary antioxidant enzymes decreased.