Trellising, fruit thinning and defoliation have only small effects on the performance of `Ruby Seedless grape in Morocco

The effects of trellising, thinning and defoliation on growth, yield and fruit composition were investigated in grape (Vitis vinifera L., `Ruby Seedlessʹ) in Morocco over two years. Vines were grown on a double tee (DT) or a triple tee (TT) using two or three cross-arms, thinned at fruit set (29 clusters) or not thinned (35 clusters), and defoliated (removal of basal leaves at veraison up to and including the leaf opposite the first retained grape cluster) or left undefoliated. The TT trellis had greater shoot growth, leaf area, and pruning weights than the DT trellis. Twenty per cent of light reached the fruiting zone in both trellis systems. In contrast, average light in this zone ranged from 52 to 969 µmol m-2 s-1 in the defoliated vines compared with 13 to 59.µmol m-2 s-1 in the undefoliated vines. Berries on defoliated vines were up to 6.K warmer than berries on the control vines. Yield per vine was not affected by any of the treatments, with an average yield of 7.53 ± 1.85.kg per vine. Average berry weight was increased by 6% with either defoliation or fruit thinning. Total soluble solids were significantly (P<0.05) increased in thinned vines (17.02±0.10°Brix) compared with unthinned vines (16.55±0.09°Brix), whereas there was no effect of trellising and defoliation on total soluble solids. Defoliation increased fruit colour slightly in unthinned vines (absorbance values at 520 nm of 0.390 and 0.461), while thinning increased berry colour slightly in undefoliated vines (absorbance values at 520 nm of 0.390 and 0.489). Trellising, fruit thinning and defoliation have only marginal effects on the performance of grape in Morocco.