A comprehensive study on the effect of foliar mineral treatments on grapevine epiphytic microorganisms, flavonoid gene expression, and berry composition

Foliar treatments with mineral-based compounds have aroused interest as a sustainable approach to cope with high-temperature stress in vineyards, improving the colour of grapes and wines without altering the sugar concentration. Since berry-associated microorganisms are crucial for wine production, composition and stability, the present study aims to unravel the effects of kaolin and zeolite treatments on berry quality, flavonoid gene expression and epiphytic microorganisms (total fungi, Hanseniospora uvarum, Metschnikowia pulcherrima, plant-associated bacteria and lactic acid bacteria). Experiments were performed on 'Sangiovese' during ripening in two growing seasons (2019 and 2020). Both mineral treatments were able to cause the elicitation of several flavonoid-related genes and to increase the anthocyanin concentration in berries without an alteration of the final technological maturity (TSS, TA, pH) of the grapes. Interestingly, neither kaolin nor zeolites negatively affected the analysed microbial population at harvest despite transient alterations observed in the more stressful year (2019). These results support the use of foliar mineral treatments to increase anthocyanin concentration in grape berries and protect them from excessive heat without altering their native microorganisms.