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 the rachis browning and extending the storage life of 'Fakhri' table grape. The abscission zone of grape clusters was immersed in solutions of melatonin (MT) (250 and 500 µM), cytokinin (CK) (50 and 100 mM), gibberellin (GA) (50 and 100 mM), or auxin (IAA) (50 and 100 mM), for 5 min then stored at 2.5 ± 1 °C and 90–95 % relative humidity for 30 d. The hormonal treatments significantly delayed rachis browning by reducing phenolic oxidation and the activity of key browning enzymes (polyphenol oxidase and peroxidase). Treated rachises maintained higher relative water content and chlorophyll levels, supported by enhanced antioxidant enzyme activity (catalase, superoxide dismutase) that mitigated oxidative stress markers like malondialdehyde and hydrogen peroxide. Hormonal analysis revealed a favorable shift, with increased levels of auxin and gibberellin and a concurrent decrease in abscisic acid in rachis, further confirming delayed senescence. In berries, the hormonal applications prevented firmness loss, reduced weight loss, and better preserved ascorbic acid content. Among all treatments, 500 µM MT, 100 mM CK, and 100 mM IAA were the most effective in maintaining overall visual and nutritional quality. In conclusion, postharvest hormonal treatment, particularly with MT, CK, or IAA, represents a highly promising strategy for suppressing rachis browning and extending the commercial storage life of table grapes by enhancing antioxidant defenses and modulating endogenous hormone balance.