A four-year trial (1999–2002) was carried out in commercial vineyards in order to test the effect of manual leaf removal in the cluster zone at veraison on grape yield, berry composition, and stilbene concentration at harvest. Two Vitis vinifera L. red wine cultivars (Barbera and Croatina) and one white wine cultivar (Malvasia di Candia aromatica) were considered. The vines were Guyot trained, with 10 shoots per meter of row, and leaf removal accounted for approximately 22% of removed canopy surface. Meteorological data were recorded, as well as grape production, fruit composition, and stilbenes (trans-resveratrol, trans-piceid, cis-piceid) at harvest. Grape yield was not affected by leaf removal in any of the tested cultivars. Grape sugars and acidity were affected by leaf removal differently depending on meteorological conditions and cultivar. Leaf removal increased trans-piceid grape concentration in Barbera and decreased trans-resveratrol and cis-piceid in Croatina and Malvasia di Candia aromatica under cool meteorological conditions. Leaf removal had no effect on stilbene grape concentrations under warmer and drier climatic conditions.
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