Abstract: In this study, we investigated the effect of cluster thinning on flavonoids compounds in Cabernet Sauvignon grape skin. The results showed that cluster thinning increased berry mass and horizontal diameter. In addition, it increased the contents of reducing sugar and soluble solid and reduced total acid content. A total of 18 monomeric anthocyanins, 6 flavanols and 15 flavonols were determined in grape skins for each level of cluster thinning. Compared with the control group without cluster thinning, the contents of anthocyanins and flavonols in grape skins increased by 4.43% and 10.89% after 27% of clusters were thinned per plant, respectively, and increased by 16.59% and 77.80% in grape skins after 54% of clusters were thinned, respectively. Principal component analysis (PCA) and cluster analysis (CA) further showed that the contents of flavonoids in grape skins significantly increased after cluster thinning, and the first and second principal components (PC1 and PC2) explained 45.24% and 28.87% of the total variance, respectively. Overall, both 27% and 54% cluster thinning increased the contents of flavonoids in grape skins, but the former is recommended taking into consideration flavonoids contents and economic?benefits.

Key words: cluster thinning; Cabernet Sauvignon; flavonoids