Stimulatory effect of bunch thinning on sugar accumulation and anthocyanin biosynthesis in Shenhua grape berry (Vitis vinifera x V-labrusca)

Background and Aims: Bunch thinning (BT) is a cultivation approach that strongly influences sugar and anthocyanin accumulation in grapes. Until now, little has been reported describing its underlying mechanisms. The aim was to explore the impact of BT on berry composition, enzyme activity, anthocyanin biosynthesis and gene expression from veraison to harvest in Shenhua grape berries. Methods and Results: Vines cultivated in a greenhouse were selected and randomly divided into a Control group and a BT group in which half of the total bunches of each vine were removed 1 week before veraison. Bunch thinning positively influenced the sugar concentration, which could be attributed to the enhanced activity of acid invertase and sucrose synthase (cleavage direction). Bunch thinning also increased the anthocyanin concentration of berry skins significantly, which might be related to the positive upregulation of the expression of most genes involved in anthocyanin biosynthesis. Moreover, the downregulation of F3' H and upregulation of F3'5'H may be responsible for the observed shift of the anthocyanin composition under BT. Conclusion: Bunch thinning increased both the sugar accumulation and anthocyanin biosynthesis and positively upregulated the activities of two enzymes, as well as the expression of most of the genes related to anthocyanin biosynthesis. Significance of the Study: These findings provide insight into the effect of BT on the sugar accumulation and anthocyanin biosynthesis of grape berries.