Virulence Spectrum and Molecular Characterization of Xanthomonas oryzae pv. oryzae Infecting Rice

Abstract

Background: Bacterial leaf blight (BLB) is a major bacterial disease of rice, causing serious yield losses in endemic regions. Continuous surveillance and characterization of pathogen variability are essential for effective disease management. Methods: A roving survey was conducted during 2025 in major rice-growing areas of the Chengalpattu district, Tamil Nadu. Diseased samples were collected from different rice varieties and subjected to isolation using the maceration technique. The per cent disease index (PDI) was calculated and documented. Morphological, cultural, pathogenicity analysis and molecular characterization (16S rRNA sequencing) were performed to confirm the pathogen. Virulence variability among ten isolates was assessed using clip inoculation on rice variety CO51. Result: The disease severity ranged from 40 to 85%, with CO51 recording the highest susceptibility (85%) among the reported varieties. All the study isolates exhibited circular, smooth, yellow, mucoid colonies on Nutrient Agar and were Gram-negative rods. Pathogenicity tests reproduced typical BLB symptoms and fulfilled Koch’s postulates. Molecular analysis confirmed 100% similarity with Xanthomonas oryzae pv. oryzae in the database. Significant variation in virulence was observed, with isolate 1(YNX001) recording the highest PDI. The study confirmed the prevalence of virulent BLB strains in Chengalpattu district and highlights the need for integrated disease management strategies.