Berry ripening and evapotranspiration in Vitis vinifera L.

Based on the observation that the allometric situation, i.e., the ratio between berry volume and skin area (smaller vs. larger fruit), and the physical intactness of the skin are paramount in determining final sugar content of mature grapes, water efflux (Jw) by evapotranspiration is hypothesized to be the driving force of berry sugar import and accumulation. This reduction of the physiological process of hexose accumulation to non-metabolic variables allows an assessment and prediction of berry assimilate uptake by relatively simple mathematical equations. Measurements of hexose concentrations and berry diameter in three consecutive years were used to test the model. The post-veraison period was found to separate into two distinct phases with different water flux characteristics. From this emerges that the water status of vine and particularly the conditions in the grape zone must be of practical importance in determining the rate of sugar accumulation during grape ripening.