Effects of different cluster sunlight exposure levels on ripening and anthocyanin accumulation in Nebbiolo grapes

The influence of solar radiation and temperature on the accumulation of berry skin anthocyanins was evaluated in Vitis vinifera L. cv. Nebbiolo during ripening. In 2006 and 2007, five fruit zone light exposure regimes were set up using plastic netting or leaf removal. Shading was applied in three different periods: from fruit set to veraison, from fruit set to harvest and from veraison to harvest. Fruit zone shading had no impact on yield per vine and cluster weight, but early fruit zone shading caused a slight delay in berry development, although this did not lead to lower berry size at harvest. Fruit zone shading had a negative effect on total soluble solids (TSS) and anthocyanin accumulation. Generally, fruit shading induced a decrease in dihydroxylated anthocyanin concentration and an increase in trihydroxylated anthocyanin concentration. Fruit zone leaf removal caused a delay of berry development, but did not affect either berry size or cluster weight or yield at harvest. Excessive sun light exposure caused sunburn damage and did not increase TSS or anthocyanin accumulation.