The effect of early leaf removal on whole-canopy gas exchange and vine performance of <i>Vitis vinifera</i> L. ‘Sangiovese’

Abstract

The physiological effects induced at the whole canopy level by early vine defoliation, which has already proven to be very effective in reducing crop via diminished fruit-set while achieving loose clusters and better must quality, was investigated. Fruiting ‘Sangiovese’ vines grown in large pots were subjected to a pre-bloom defoliation (D) by removing the first six basal leaves from each shoot and compared to non-defoliated control (ND). Vegetative growth and grape yield and composition were assessed along with seasonal canopy net CO₂ exchange rates (NCER) measured via an enclosure method. While confirming that early defoliation sharply reduced fruit set, cluster compactness and yield per shoot, the post-treament seasonal NCER/vine data were slightly higher in ND vines (13.3 μmol·s^-1 vs. 12.2 μmol·s^-1 recorded for D canopies). Yet, when these data were given on a per unit of area basis, defoliated vines showed higher rates than ND vines (4.75 μmol·m^-2·s^-1 vs. 4.16 μmol·m^-2·s^-1). Overall, NCER/yield (shoot basis) increased by 38 % in D vines, thus resulting in enhanced carbohydrate content for ripening; this finding accords well with advanced maturation and highly improved must soluble solids concentration. The solid physiological background of this early defoliation technique now warrants further investigation in terms of mechanical viability.