Molecular Confirmation of Agroathelia rolfsii as the Causal Agent of Watermelon Fruit Rot in Brazil and Comparative Aggressiveness on Watermelon and Melon

ABSTRACT This study provides the first molecular confirmation of Agroathelia rolfsii as the causal agent of preharvest watermelon fruit rot in Brazil and evaluates the pathogenic variability of A. rolfsii and the related species A. delphinii on cucurbit fruits. Morphological and phylogenetic analyses based on ITS and LSU rDNA confirmed the identity of A. rolfsii isolates obtained from symptomatic fruits. Aggressiveness assays, measured by lesion severity, demonstrated that A. rolfsii reproduced typical field symptoms on watermelon cultivars Crimson Sweet and Baby, fulfilling Koch's postulates. Lesion severity varied among isolates, with COUFPI 277 being the most aggressive A. rolfsii strain. A. rolfsii also induced mild rot on melon cv. Canary but not on Piel de Sapo. Notably, A. delphinii isolates were also pathogenic to watermelon, sometimes producing larger lesions than A. rolfsii . These results expand the known host range of A. delphinii and emphasise the need for accurate molecular identification within the Agroathelia – Sclerotium complex for effective disease management.