Effect of cluster thinning on berry skin anthocyanin composition of Vitis vinifera cv Nebbiolo

Cluster thinning (removal of 50 % of the cluster one month after bloom) was tested for three consecutive years in a vineyard located in southern Piedmont (Italy). At harvest, the concentrations of total anthocyanins and flavonoids were assessed by spectrophotometry, and the concentrations of individual anthocyanins determined by HPLC. Berry weight and berry skin weight slightly increased following thinning. Soluble solids and berry skin anthocyanins and flavonoids were more concentrated in berries from cluster thinned plants. Cluster thinning increased the concentrations of cyanidin-3-glucoside and peonidin-3-glucoside and, to a lesser extent, petunidin-3-glucoside. The concentrations of malvidin-3-glucoside and of acylated anthocyanins were not affected by cluster thinning.