Differential effects of shading fruit or foliage on the development and composition of grape berries

Abstract

Grape vines ( Vitis vinifera L. cv. Cabernet Sauvignon) were selectively shaded with polypropylene doth to separate the effects of shading fruit from the effects of shading foliage on berry development and on the accumulation patterns of sugar, anthocyanins, malate, tartrate and potassium in the fruit. Shading the foliage led to both a delay and a decrease in berry growth. Leaf shading also affected the timing and the magnitude of sugar accumulation. Total sugar per berry was reduced more by shading than was sugar concentration because of the simultaneous effect of shading on fruit size. The rate of pre-veraison malate accumulation, the maximum malate content at veraison, and the rate of post-veraison malate loss in the berries were all highest in the fully sun-exposed vines and were progressively lower with increasing foliage shade. Tartaric acid was significantly lower in fruit from heavily shaded vines than in fruit from the more exposed treatments. Leaf shading was also significantly correlated with an increase in potassium concentration in the fruit. At harvest, juice pH was more dosely correlated with the concentrations of tartaric acid and potassium in the berries than with malate content. Grapes from heavily shaded vines had the highest pH. Anthocyanin accumulation in the fruit was affected more by duster shading than by leaf shading. Shaded fruit had significantly less anthocyanin than sun exposed fruit. These results indicate that in addition to a general delay in ripening there were also specific effects of shading on individual components of berry composition, and that the specific effects were different for leaf and duster shading.