Yield Components, Vegetative Growth and Fruit Composition of ‘Istrian Malvasia’ (Vitis vinifera L.) as Affected by the Timing of Partial Defoliation

The influence of partial defoliation performed at different grapevine growth stages on yield components, vegetative growth and fruit composition of ‘Istrian Malvasia’ (‘Malvazija istarska’) vines was investigated. During two consecutive seasons partial defoliation was performed manually at three grapevine growth stages; before bloom (BB), after bloom (AB), and at the beginning of bunch closure (BC). Three to four leaves on the basal part of primary shoots were removed in order to obtain moderately open grapevine canopy with good bunch exposure to sunlight. Control treatment without partial defoliation was also included. Partial defoliation did not significantly affect any of yield components of ‘Istrian Malvasia’ vines. The only consistent response to partial defoliation was the regrowth of laterals if partial defoliation was done early in the season, leading to the recovering of the removed leaf area from primary shoots. Less intensive regrowth of laterals occurred on BC treatment, resulting in the smallest leaf area per vine and the lowest leaf area/yield ratio, but the differences among treatments were not significant. Basic composition of ‘Istrian Malvasia’ grape juice (soluble solids, titratable acidity and pH) was not significantly affected by the timing of partial defoliation, but soluble solids tended to be higher in BB treatment and lower in BC treatment. It is concluded that the removal of three to four leaves per shoot at different grapevine growth stages did not considerably affect yield components and basic fruit composition of ‘Istrian Malvasia’ vines.