Diversity and pathogenicity differences among Acidovorax citrulli strains causing bacterial fruit blotch in cucurbit crops

Abstract

This study investigates the genetic diversity and pathogenicity differences among eight Acidovorax citrulli isolates causing bacterial fruit blotch (BFB) in cucurbit crops. Using a polyphasic approach combining biochemical assaysmolecular identification via species-specific Polymerase Chain Reaction (PCR) and Repetitive Element PCR (REP-PCR) fingerprintingthe isolates were characterized to confirm identity and assess genetic relationships. Biochemical tests showed homogeneous profiles consistent with A. citrulli. Molecular analysis confirmed species identity with a specific 360 bp PCR product. Genetic fingerprinting revealed two main clusters: one comprising isolates Ac01–Ac06 with high genetic similarityand a distinct cluster containing Ac07 and Ac08with Ac08 being the most genetically unique. Pathogenicity tests on watermelonmelonand cucumber demonstrated significant variation in virulence among isolates (disease severity ranges: 30.0-96.0% for cucumber60.0-98.0% for melon53.0-100.0% for watermelon)with watermelon exhibiting the highest overall susceptibility to most bacterial strains and Ac08 displaying the highest aggressiveness across all hosts (97.3% average severity)suggesting a broad host range. The study confirms the presence of two major lineages corresponding to known Group I and Group II classificationshighlighting the importance of considering genetic and pathogenic diversity for effective disease management and breeding programs. These findings underscore the critical role of molecular diagnostics in seed certification and BFB control strategies.