Strengthening grapevine berry physiology and composition through kaolin-silicon foliar applications under summer...

The increasing frequency of heat and drought events in Mediterranean vineyards threatens vine performance and berry quality. Kaolin (Kl) particle films combined with silicon have been proposed as mitigation strategies to reduce temperature and improve plant water status; however, their effects on berry structure and metabolism remain uncertain.

This study evaluated the foliar application of MiKS, a formulation combining 2% kaolin (Kl) with increasing silicon concentrations (2-8%, v/v), on berry skin structure, cuticular wax composition, metabolite profile, and wine volatile composition of the Touriga Nacional variety grown in the Douro region over two growing seasons.

MiKS treatments promoted significant structural reinforcement of berry skin by increasing cuticle thickness at both veraison and harvest. These anatomical changes were associated with a substantial remodeling of cuticular wax composition, characterized by a predominance of pentacyclic triterpenoids, particularly oleanolic acid, and a reduction in the relative abundance of carboxylic acids. Berry metabolism responded in a stage- and season-dependent manner, with changes in phenolic compounds, organic acids, amino acid-related metabolites, and flavan-3-ols. Carbon isotope discrimination (δ¹³C) indicated improved water status under MiKS 2, whereas technological ripening remained balanced. MiKS treatments also reduced volatile acidity and altered wine volatile organic compound profiles, with higher silicon concentrations promoting esters and alcohols associated with fruity and floral aroma characteristics.

The combined application of kaolin and silicon promoted coordinated structural, physiological, metabolic, and oenological responses while preserving grape technological quality, highlighting MiKS as a promising sustainable foliar strategy to improve grapevine resilience under Mediterranean summer stress.