Location: Horticultural Crops ResearchTitle: Foliar reflective film and water deficit increase anthocyanin to soluble solids ratio during berry ripening in Merlot
Submitted to: American Journal of Enology and Viticulture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/1/2015
Publication Date: 8/1/2015
Citation: Shellie, K. 2015. Foliar reflective film and water deficit increase anthocyanin to soluble solids ratio during ripening in Merlot. American Journal of Enology and Viticulture. 66:348-356.
Interpretive Summary: Recent warming trends and erratic weather patterns in wine grape production regions have evoked a need for adaptive cultural practices that ameliorate deleterious influences of weather events on berry ripening and preserve or enhance berry composition for wine production. A key finding from this study was that a foliar application of a white colored, kaolin clay-based reflective film to the vine canopy during berry development enhanced the red color of the berry during ripening in the wine grape cultivar Merlot under warm, arid growing conditions with high solar radiation. The reflective film did not have any detectable influence on yield or plant-soil water relations. The findings from this study are of commercial interest to growers in warm production regions where elevated temperatures during ripening may inhibit berry color development and deleteriously alter the color to alcohol balance of the resulting wine.
Technical Abstract: Elevated temperature 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. In this study, we tested the effectiveness of a foliar reflective film to increase the ratio of anthocyanin to soluble solids in Merlot grapevines. Vines were irrigated to provide 90 or 35% of their estimated water demand (DI90 and DI35, respectively) and sprayed with a kaolin-based reflective film in a replicated, split-plot experimental design over multiple growing seasons. Cluster removal prior to bloom was added as an additional split during the last three years of the study to determine whether crop load influenced vine response to the reflective film. The reflective film increased the ratio of anthocyanins to soluble solids during ripening under both irrigation amounts and crop loads, but its effectiveness declined at high concentrations of berry soluble solids. The reflective film did not alleviate water-deficit-associated decreases in yield, berry weight or titratable acidity. Vines with reflective film contained a fewer number of berries per cluster than vines without reflective film and, in vines under DI90, the reflective film increased berry fresh weight and anthocyanin content per berry. The ratio of anthocyanins to soluble solids at veraison and harvest was higher in vines irrigated at DI35 than at DI90. Cluster removal had no detectable effect on the ratio of anthocyanins to soluble solids at harvest. Results from this study indicate that a foliar reflective film in combination with vine water deficit can increase the ratio of anthocyanins to soluble solids in Merlot grapevines grown under warm, arid conditions.