Leaf area to fruit weight ratios for maximising grape berry weight, sugar concentration and anthocyanin content during ripening

Vineyard management requires the maintenance of the leaf area per unit weight of fruit necessary for growing grapes without detrimental effects on fruit composition. Leaf removal and bunch thinning experiments have previously shown some effects on berry composition. Several berry compositional parameters (e.g. berry weight, sugar concentration and colour) increase with leaf area to fruit weight ratio until reaching an optimum or saturation point. Further increases in the ratio do not have any significant effect. However, optimum ratios from previous experiments have been determined only at harvest and they are highly variable. Irrigated Merlot grapevines were used to study the relationship between leaf area to fruit weight ratio and mean berry weight, sugar concentration and anthocyanin content during ripening. Four defoliation treatments were applied to individual girdled shoots at berry pea size stage. After veraison, leaf and fruit samples were collected weekly until berry maturity and leaf area, fruit weight per shoot, berry weight, sugar concentration and anthocyanins were measured. Berry weight, sugar concentration and anthocyanin content were correlated with leaf area to fruit weight ratio from veraison through to maturity. The fitted regressions allowed us to determine the ratios that maximised the measured compositional parameters. Leaf area per fruit weight necessary for maximum berry weight was more variable than that for sugar concentration and anthocyanin content. Greater leaf area to fruit weight was required for maximising anthocyanin content than that for sugar concentration. We defined optimum leaf area to fruit weight ratios within certain ranges for the ripening period in our vineyard.