Background and Aims:  Little work has been conducted on the effects that summer pruning operations have on the relative growth of grapevine berry parts. Our paper studies whether pre‐bloom leaf removal is able to modify the proportions of seed, skin and flesh in ripe grapevines berries and the related effects on must composition. Methods and Results:  Pre‐bloom defoliation (D) of the first six basal leaves on main shoots was applied to the field‐grown cvs Barbera and Lambrusco salamino (Vitis vinifera L.) in Italy's Po Valley and compared with non‐defoliated controls. D showed reduced fruitset, hence yield per shoot, and concurrently improved must soluble solids and total anthocyanins in both cultivars as a likely result of increased leaf‐to‐fruit ratio (+3.4 cm2/g and +5.2 cm2/g for Barbera and Lambrusco, respectively) and improved relative skin mass (from 6.0 to 9.0% in Barbera and from 8.1 to 10.4% in Lambrusco). In both cultivars, skin and seed mass were highly correlated with total berry mass and changes in relative skin mass were generally not related to berry size. Conclusions:  These results indicate that berry size per se is not the primary factor in determining final grape composition, which instead seems to depend upon factors differentially affecting the growth of the various berry components. Significance of the Study:  Pre‐bloom D induced a consistent, site and cultivar‐independent increase in relative skin mass suggesting this effect being strongly physiologically regulated.

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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.

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