Effects of Gibberellic Acid on Soluble Sugar Content, Organic Acid Composition, Endogenous Hormone Levels, and Carbon Sink Strength in Shine Muscat Grapes during Berry Development Stage

The phytohormone gibberellic acid (GA3) is widely used in the table grape industry. However, there is a paucity of information concerning the effects of GA3 on fruit quality and sink strength. This study investigated the effects of exogenous GA3 treatments (elongating cluster + seedless + expanding, T1; seedless + expanding, T2; expanding, T3; and water, CK) on the content of sugars, organic acids, and endogenous hormones and sink strength. Results showed that T2 treatment displayed the highest fructose and glucose levels at 100 days after treatment (DAT), whereas its effect on tartaric acid, malic acid, and citric acid concentrations at 80 and 100 DAT was relatively weak. Under GA3 treatments, GA3, IAA, and CTK contents increased, whereas ABA content decreased at 1, 2, 4, 8, and 48 h. Analysis of sugar phloem unloading revealed that T2 treatment exhibited the highest values during softening and ripening stages. Our findings indicate that appropriate GA3 application can positively influence sink strength by regulating sink size and activity, including berry size enlargement, sugar phloem unloading, and sugar accumulation in grape sink cells.