Cluster thinning influences photosynthetic activity, fruit composition and wine quality of grapes under tropical environment

Abstract

A field experiment was conducted during the year 2014-15 to study the effect of cluster load on yield, berry quality, gas exchange and biochemical changes in Chenin Blanc and Syrah wine grape varieties. Cluster load was adjusted to 40, 60 and 80 clusters/vine. Significant differences were observed for all physicochemical and biochemical parameters. The increased bunch weight in Chenin Blanc (112.88 g) and Syrah (92.44 g) was recorded with the reduction in number of clusters per vine (40 clusters). The same trend was also observed for 100 berry weight. The reduction in cluster load/vine increased the total soluble solids in berries of both the varieties. Significantly higher rate of photosynthesis was recorded with maximum cluster load in Chenin Blanc while in Syrah variety; the rate of photosynthesis was highest with reduced cluster load. In Chenin Blanc, highest concentrations of reducing sugar, proteins, phenols and total carbohydrate were recorded in 40 clusters/vine. On the other hand, in Syrah variety, it was with 60 clusters/vine. The titratable acidity and pH of the must was significantly influenced by cluster thinning treatments. The vines with minimum clusters (40 clusters) showed minimum titratable acidity and pH while the maximum clusters load increased titratable acidity and pH. It was observed that the source: sink alteration by cluster load in both the varieties had positive impact on yield, berry quality, sugar accumulation, gas exchange parameters and biochemical composition.