Involvement of grape berry morpho-anatomy and polyphenol content with the severity of grape ripe rot

Abstract Grape ripe rot (GRR), primarily caused by Colletotrichum species, severely affects grape production and wine quality, especially under the favorable climatic conditions of southern Brazil. This study aimed to investigate the relationship between berry skin morpho-anatomical traits, polyphenol content, and GRR severity in 13 grapevine genotypes, eight of which have genes that confer resistance to powdery and downy mildew. Pathogenicity bioassays were conducted using an isolate from the C. acutatum species complex, applied under various inoculation methods across four crop seasons (2019–2022). Scanning electron microscopy (SEM) revealed clear structural degradation in symptomatic berries, particularly in susceptible varieties like Sauvignon Blanc and Merlot. Conversely, resistant genotypes such as PI4407 and Bronner exhibited thicker cuticles and intact epidermal layers. Biochemical analysis showed that polyphenol content tended to increase in response to higher disease severity, especially in Regent and Prior. However, naturally resistant varieties like Concord and Calardis Blanc maintained low disease progression and low polyphenol accumulation, suggesting alternative defense mechanisms. Statistical analysis of the Area Under the Disease Progress Curve (AUDPC) and polyphenol concentration confirmed genotype-specific responses to infection and stress. These findings reinforce the potential of combining anatomical and biochemical markers to guide breeding programs and improve disease management strategies in viticulture.