Effects of gibberellin applications before flowering on the phenotype, ripening, and flavonoid compounds of Syrah grape berries

Background: Vitis vinifera L. cv. Syrah grapevines in most Chinese viticulture regions generally have compact clusters that increase the susceptibility to diseases and inhibit coloration of the inner berries. Gibberellic acid (GA₃ ) is a plant growth regulator that is widely used during grape cultivation to elongate the rachis, control fruit set, and decrease cluster compactness. In this study, Syrah grapevines were treated with GA₃ before flowering in 2019 and 2020 to determine the optimal GA₃ treatment concentrations and times for decreasing bunch compactness, while minimizing the negative effects on the wine grape cluster weight.

Results: Pre-flowering GA₃ applications at 3, 5, and 7 mg L^-1 , especially treatment at 20 days before flowering, decreased Syrah grape bunch compactness by decreasing the fruit set rate and promoting bunch elongation, with minimal adverse effects on the healthy grape cluster weight in both years. The 7 mg L^-1 GA₃ treatment at 20 days before flowering significantly increased reducing sugar, total phenolic, tannin, and total anthocyanin contents of Syrah grape berries in 2019 and 2020. Moreover, high-performance liquid chromatography-electrospray ionization-tandem mass spectrometry, hierarchical cluster, and principal component analysis results indicated GA₃ applications before flowering (3, 5, and 7 mg L^-1 ) significantly affected the accumulation of different anthocyanins in Syrah grape berries. Notably, the application of 7 mg L^-1 GA₃ at 20 days before flowering resulted in the highest anthocyanin content.

Conclusion: Pre-flowering gibberellin application can decrease bunch compactness and improve the quality of Syrah grape berries. These findings reflect the potential utility of gibberellin treatments for decreasing cluster compactness and increasing the quality of wine grapes. © 2022 Society of Chemical Industry.