Abstract Melanie FordMichael QianBhaskar Bondada

Bunch Exposure Management in a Challenging Environment Using Sun Protection Agents

Melanie Ford,* Michael Qian, and Bhaskar Bondada 
*Washington State University, Wine Science Center, 2710 Crimson Way, Richland, WA 99354 (bbondada@wsu.edu)

Recent warming trends and erratic weather patterns have increased the incidence of sunburn injury to grape berries, necessitating the use of sun protection agents. The objective of this study was to determine the effects of kaolin (Surround WP) and calcium carbonate on fruit composition, including aroma characteristics, in Cabernet Sauvignon. These sun protection agents were applied just after fruit set at the manufacturer’s recommended dosage until runoff using a backpack sprayer over the fruit zone and the whole canopy. Vines and shoots without the agents served as untreated controls. Sunburned berries showed degradation of crystalline wax structure, while such structures remained intact in clusters sprayed with sun protection agents. Sunburned berries of all cultivars dehydrated, concentrating the TSS, reducing fermentable sugars, potassium, and organic acids and increasing pH. Among the phenolic compounds, total anthocyanins and amount of individual anthocyanins were reduced significantly, while quercetin levels increased in sunburned berries. The levels of various volatile aroma compounds such as terpenoids, C13-norisoprenoids, and C6 compounds varied among treatments. The composition of clusters sprayed with sun protection agents was not compromised, while both kaolin and CaCO3 showed similar effects. 

Funding Support: WSU Viticulture and Enology Scholarship

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