Phytochemical Concentrations and Antioxidant Capacity of Grapes Treated with Low Copper Formulations against Downy Mildew

Abstract

A two-year study was conducted in an organic vineyard to evaluate the phytochemical concentrations and antioxidant capacity of grapes treated with low copper for downy mildew control compared to grapes that were untreated or treated with a standard fungicide. The metabolic profile, antioxidant capacity, and downy mildew incidence and severity were assessed. The maturity of grapes was an important factor in determining the potential risk for the spread of fungal disease, as suggested by principle components analysis (PCA), which showed a positive relationship between tartaric acid concentration and both incidence and severity of downy mildew disease. Polyphenols and thiols were more abundant in berries with less disease. The thiols were highly correlated with the antioxidant capacity, indicating an important role of these metabolites in determining the antioxidant potential of grape berries. Moreover, both the antioxidant indexes and thiols in the PCA were plotted opposite the disease severity and incidence, suggesting that higher antioxidant potential may be responsible for an increased capacity of grapes to counteract the disease. Results showed that low-copper formulations could control grape downy mildew in the field with a similar efficacy to the standard reference fungicide, without affecting the phytochemical profile and the antioxidant potential of grapes. Low-copper formulations may be thus considered alternatives for organic agriculture that minimize costs and copper accumulation in the soil, thus ensuring grape quality in a sustainable crop management system.