Inhibiting rachis browning in table grape by postharvest hormonal treatments: Regulation of internal hormone homeostasis

This study investigated the efficacy of postharvest hormonal treatments in preventing rachis browning and extending the storage life of ‘Fakhri’ table grape. The abscission zone of grape clusters was immersed for 5 min in solutions of melatonin (MT; 250, 500 µM), cytokinin (CK; 50, 100 mM), gibberellin (GA; 50, 100 mM), or auxin (IAA; 50, 100 mM), then stored at 2.5±1°C and 90–95 % RH for 30 d. Hormonal treatments significantly delayed rachis browning (40 % reduction by MT500 at 30 d) by suppressing key browning enzymes (25 % reduction in peroxidase and 55 % in polyphenol oxidase by MT500 at 30 d). Treated rachises maintained higher relative water content and chlorophyll levels, supported by enhanced antioxidant enzyme activity (103 % increase in catalase by MT500 and 65 % in superoxide dismutase by MT500 at 30 d), which mitigated oxidative stress markers (23 % reduction in malondialdehyde by MT500 and 34 % reduction in hydrogen peroxide by CK100 at 30 d). Hormonal analysis revealed increased endogenous auxin and gibberellin levels (by 379 % with IAA100 and 132 % with GA100 at 30 d) and decreased abscisic acid (by 50 % with IAA100 at 30 d) in the rachis. In berries, hormonal applications prevented firmness, reduced weight loss, and better-preserved ascorbic acid content. Among all treatments, MT500, CK100, and IAA100 were most effective in maintaining overall visual quality. In conclusion, postharvest hormonal treatment, represents a promising strategy for suppressing rachis browning and extending the commercial storage life of grape.