Seasonal Temperature Variation Shapes Anthocyanin Composition and Berry Coloration in ‘Summer Black’ Grape

Berry coloration in ‘Summer Black’ grape is strongly influenced by anthocyanin composition. This study investigated how seasonal temperature variation affects anthocyanin profiles and berry coloration. Winter berries accumulated significantly higher anthocyanin levels than summer berries, with total anthocyanin content reaching 2405.38 μg/g FW (fresh weight), compared with 1440.94 μg/g FW in summer berries. Winter berries exhibited a distinct pigment profile enriched in trihydroxylated anthocyanins, and delphinidin accumulation was 2.27-fold higher than that in summer berries at the final developmental stage. Lower winter night temperatures were associated with higher F3′5′H expression. In contrast, higher summer night temperatures were associated with increased F3′H expression and cyanidin accumulation, resulting in a greater proportion of dihydroxylated anthocyanins and lighter berry coloration. These findings suggest that seasonal temperature variation, particularly night temperature under the tested double-cropping conditions, is closely associated with anthocyanin composition through differential regulation of the F3′H and F3′5′H branches of the flavonoid pathway, providing insights into the environmental regulation of berry pigmentation and quality formation in grape.