Foliar Reflective Film and Water Deficit Increase Anthocyanin to Soluble Solids Ratio during Berry Ripening in Merlot

Abstract

Elevated temperatures can decrease the ratio of anthocyanins to soluble solids in red-skinned berries, and warming trends in grape production regions have raised concern about color to alcohol balance in wines produced from fruit with altered ratios. This study investigated the effect of a foliar reflective film on the ratio of anthocyanins to soluble solids in deficit-irrigated Merlot grapevines over a 5-year period. Vines were irrigated to provide 90 or 35% of estimated water demand (DI90 and DI35, respectively) and were either sprayed with a kaolin-based reflective film or left unsprayed using a replicated, split-plot design. During the 2008–2010 seasons, crop load was adjusted in half of the vines within each subplot by removing 50% of clusters prior to bloom. Regardless of crop load, the reflective film increased the ratio of anthocyanins to soluble solids in DI90 and DI35 when the concentration of soluble solids was 18 to 24%. The reflective film did not alleviate the decrease in yield or titratable acidity associated with water deficit, and it had no influence on yield per vine. However, it reduced the number of berries per cluster, especially in DI35-irrigated grapes. In DI90-irrigated vines, decreased berry number per cluster was associated with increased berry fresh weight and anthocyanin content per berry. Cluster removal influenced berry composition at harvest only under DI35 irrigation. The ratio of anthocyanins to soluble solids during ripening was higher in DI35-irrigated plants than in those under DI90 irrigation. Taken together, foliar reflective film combined with deficit irrigation increased the ratio of anthocyanins to soluble solids under arid conditions with high solar radiation.