Late leaf removal aimed at delaying ripening in cv. Sangiovese: Physiological assessment and vine performance

Background and Aims: Global warming is inducing a general earliness in the onset of grapevine phenological stages including ripening, a phenomenon that occurs often in the hottest seasons and which leads to unbalanced wines. Our aim was to assess the physiological basis of late leaf removal applied above the bunch area as a tool for delaying ripening. Methods and Results: Potted cv. Sangiovese grapevines were subjected to leaf removal treatments applied preveraison (DEF-I) and postveraison (DEF-II) by pulling out six to seven primary leaves and laterals, if any, above the bunch zone; untouched vines served as the control. Whole-canopy net CO2 gas exchange was monitored seasonally from 9 days before DEF-I to 35 days after DEF-II. Concurrently, single-leaf gas exchange was assessed, and at harvest yield components, grape composition and the leaf-to-fruit ratio were determined. The seasonal carbon/yield ratio did not differ between treatments because of the high capacity for photosynthetic compensation shown by the DEF treatments and quantified as about a 35% higher net CO2 gas exchange per unit of leaf area per day. While ripening was temporarily retarded in both DEF treatments, with sugar content being lower and titratable acidity higher, a week later both treatments had fully or partially recovered; phenolic ripening was unaffected at either harvest date. Conclusions: Defoliation above the bunch zone applied at lag-phase and postveraison (average 12°Brix) was effective in temporarily delaying technological ripeness without affecting colour and phenolics. This result depended upon the high compensation capacity for photosynthesis shown by vines in both treatments. Significance of the Study: The data provide a preliminary yet robust physiological background for targeting better field application of the technique.