Berry thinning to reduce bunch compactness improves fruit quality of Cabernet Sauvignon (Vitis vinifera L.)

Abstract

The effects of berry thinning on bunch compactness, grape sugar accumulation and subsequent wine quality were studied in Vitis vinifera L. Cabernet Sauvignon. The experiment was carried out during two consecutive seasons in a commercial vineyard. Berries of pea size were evenly removed manually to reduce berry density in bunches. Based on the decreasing proportion of berries in one bunch, the treatment was designated as C0 (control), C¼ (a 25% decrease) and C½ (a 50% decrease). The results showed that the different berry thinning treatment lowered bunch compactness accordingly. And the content of sugar, anthocyanins, total phenols, and mass of mature berries were all significantly enhanced with decreasing compactness on the same harvested time. However, the content of titratable acidity showed an inverse change. Compared with control, the sugar and anthocyanins of berry accelerated accumulation in loose bunches during grape ripening. Furthermore, the cell wall invertase (CWI) and soluble acid invertase (SAI) of berries had higher activity during grape ripening under treatments, which was associated with upregulated transcription level of VvCWI and VvGIN2. In addition, wines obtained from treatments had a higher total phenolic index, greater anthocyanins, and lower titratable acidity than the control wine. These results suggested that berry thinning with reducing bunch compactness might control accumulation of berry sugar by upregulating activities of CWIs and SAIs in berry and change berry main chemical component influencing the wine composition.