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.