Photoselective Shade Films Affect Grapevine Berry Secondary Metabolism and Wine Composition
Lauren Marigliano, Runze Yu, Nazareth Torres,
and S. Kaan Kurtural*
*UC Davis, 1380 Oakville Grade Road, Oakville, CA, 94562
(skkurtural@ucdavis.edu)
Grapevine physiology and production are challenged by forecasted increases in temperature and water deficits. Within this scenario, photoselective overhead shade films are promising tools in warm viticulture areas to overcome climate change-related factors. The aim of this study was to evaluate the vulnerability of Cabernet Sauvignon grape berry to solar radiation overexposure and optimized shade film use for berry development. A randomized complete block design field study was conducted across two years (2020 and 2021) in Oakville, Napa Valley, CA, with four shade films (D1, D3, D4, or D5) differing in the percent of radiation spectra transmitted and compared to an uncovered control (C0). Integrals for gas exchange parameters and midday stem water potential were unaffected by the shade films in 2020 and 2021. By harvest, berries from uncovered and shaded vines did not differ in size or primary metabolism in either year. Despite precipitation exclusion during the dormant season in the shaded treatments, yield did not differ between them and the control in either season. In 2020, total skin anthocyanins (mg/g fresh mass) in the shaded treatments were greater than C0 during berry ripening and at harvest. Conversely, flavonol concentrations in 2020 were reduced in shaded vines compared to C0. The 2020 growing season highlighted the impact of heat degradation on flavonoids. Flavonoid concentrations in 2021 increased until harvest while flavonoid degradation was apparent from veraison to harvest in 2020 across shaded and control vines. Wine analyses from the 2020 vintage highlighted the importance of light spectra to modify wine composition. Wine color intensity, tonality, and anthocyanin values were enhanced in D4, while antioxidant properties were enhanced in C0 and D5 wines. Altogether, our results highlighted the need for new approaches in warm viticulture areas given the impact that light composition has on berry and wine quality.
Funding Support: Daios Plastics, Jim’s Supply, Drake Enterprises, UC Davis Department of Viticulture and Enology, UC Davis Horticulture and Agronomy Graduate Group
