Effects of Cluster Thinning and Pre-Flowering Leaf Removal on Growth and Grape composition in cv. Sangiovese

Crop regulation techniques applied as pre-flowering defoliation (D) and early cluster thinning performed at the same time (ECT) or at lag-phase of berry growth (LCT) were tested over three seasons on high-yielding cv. Sangiovese (Vitis vinifera L.) and compared to non-defoliated, un-thinned control (C) vines of the same cultivar. Treatment severity consisted of removing primary leaves and any laterals developed from nodes 1 to 6 in D and by thinning 50% of clusters chosen among distal ones or those inserted on weak shoots, in the CT plots. Despite the fact that yield per vine was not as reduced in D (-32%) as in CT treatment (-45%) in comparison to C, early defoliated vines also had largely improved sugar and total anthocyanin concentrations and highest total phenolics. Yield components were also markedly affected by treatments: D vines showed smaller clusters and berries, leading in turn to improved cluster looseness, as well as higher relative skin and seed growth. While all crop-regulating treatments led to an increase in the final leaf-to-fruit ratio, parameters of technological maturity were essentially uncoupled as equally high Brix levels corresponded to the highest TA in D and, conversely, to lowest TA and highest pH in cluster thinning treatments. Overall results show that different final yield-grape composition patterns can be reached depending upon the principle used for crop regulation as a primary consequence of a diversified degree of compensation triggered on single yield components.