Combined effect of berry size and postveraison water deficit on grape phenolic maturity and berry texture characteristics (Vitis vinifera L. 'Portugieser')

The effect of berry size and moderate water deficit on skin phenolic maturity and berry texture behaviour was studied on 'Portugieser' (Vitis vinifera L.) under green house conditions. In all berry weight categories (I: < 1.1 g; II: 1.11-1.4 g; III: 1.41-1.7 g; IV: 1.71-2 g; V: > 2,01 g) water deficit resulted in reduced sugar concentration due to decreased photosynthetic activity. Interestingly, lower phenolic concentration for unit skin mass was measured in the drought stressed treatment compared to the control, irrespective of berry size. However, the concentration of the phenolic components for one berry was lower in the well watered treatment. This phenomenon was due to the increased skin/flesh ratio of the water stressed vines. Berry skin hardness was probably in connection with its phenolic concentration for unit skin weight. Changes in several berry texture parameters were accompanied by changes in berry size. Berry hardness and skin elasticity increased with berry size in both treatments. On the other hand, skin break force, skin break energy, skin thickness showed increase/decrease only in the case of the stressed vines. This result suggests that texture properties of the water-stressed berries depend on berry size to a greater extent compared to the berries of the non-stressed vines. This phenomenon may be explained by the faster ripening of the smaller and of the water stressed berries