LAUSR

BACKGROUND Vitis vinifera L. cv. Syrah grapevines in most Chinese viticulture regions generally have compact clusters that increase the susceptibility to diseases and inhibit the 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 The pre-flowering GA3 applications at 3, 5, and 7 mg L-1 , especially the treatment at 20 days before flowering, decreased the 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 the reducing sugar, total phenolic, tannin, and total anthocyanin contents of Syrah grape berries in 2019 and 2020. Moreover, HPLC-ESI-MS/MS, hierarchical cluster, and PCA 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 applications can decrease the bunch compactness and improve the quality of Syrah grape berries. These findings reflect the potential utility of gibberellin treatments for decreasing the cluster compactness and increasing the quality of wine grapes. This article is protected by copyright. All rights reserved.