EFFECTS OF LIGHT REDUCTION AT BLOOM ON FRUITS SET IN BLACK MAGIC TABLE GRAPES CV IN EARLY AND LATE PRODUCTION CICLES

A shading experiment in ‘Black Magic’ cv was conducted in Sicily to test a new thinning method, aiming to reduce the no. berries/cluster, maximising quality and value of the production. A reduction of intercepted light was imposed at the 65 stage of the BBCH scale (50% cap fall) for 12 days. The soilless greenhouse conditions allowed two growing cycles occurring under different climate conditions, an early (end of March flowering) and a late production cycle (beginning of August flowering). During the shade treatment, net photosynthetic rate was significantly reduced by 82% and 96% in the late and early production cycles, respectively. The sum of flowers and berries dropped in the untreated vines was about 80% in the late and 17% in the early cycle, increasing to 96% and 49% in the shaded vines. This supports the hypothesis that C-starvation during bloom induces berries abscission. As a consequence of the berry number reduction (46.2 and 93.4 berries/bunch obtained in the treatment versus 96.8 and 173.0 berries/bunch in the control, in late and early cycles), the yield dropped to 47.4% and 64.0% of control vines in the late and early cycle. Bunch compactness was also reduced, 5.1 and 10.5 berries/cm of rachis in shaded vines while 8.0 and 15.1 berries/cm of rachis in the control, in late and early production cycle. The no. shot berries was reduced 62.5% in shaded vines in the early cycle. TSS in shaded vines was higher than control in both cycles. Under the viticulture viewpoint, control vines in the late production cycle had already an adequate fruit set, so thinning practice is not economical advantageous. In contrast, in the early cycle control vines produced an excessive no. berries/bunch and a high incidence of shot berries, so, in this case, shading stands for a clear agronomic benefit. The fruit set in ‘Black Magic’ cv can be considered sensitive to incident light reduction at bloom, making shading an effective and successful non-chemical method.