MOLECULAR EPIDEMIOLOGY AND PATHOTYPE DIVERSITY OF XANTHOMONAS ORYZAE PV. ORYZAE IN MAJOR RICE GROWING REGIONS AND IMPLICATIONS FOR RESISTANCE MANAGEMENT AND BREEDING STRATEGIES

Bacterial blight of rice, caused by Xanthomonas oryzae pv. oryzae (Xoo), is a major constraint to rice production, particularly in Asia. This study investigates the molecular epidemiology, pathotype diversity, and virulence evolution of Xoo populations in key rice-growing regions of South and Southeast Asia. Using a combination of molecular techniques, including multilocus sequence typing (MLST), repetitive-sequence PCR (rep-PCR), and whole genome sequencing (WGS), we analyzed the genetic diversity and pathogenicity of 120 Xoo isolates from Punjab (India), Central Luzon (Philippines), Ayeyarwady (Myanmar), and the Mekong Delta (Vietnam). Results revealed significant regional differentiation in Xoo populations, with distinct genetic lineages and virulence profiles associated with specific Xa resistance genes in rice cultivars. Comparative genomics highlighted the presence of key virulence factors, including TAL effectors and the avrXa gene family, and identified horizontal gene transfer events driving the emergence of new virulent strains. Pathogenicity assays showed differential effectiveness of Xa resistance genes, underscoring the need for region-specific management strategies. The findings provide insights into the genetic and pathogenic diversity of Xoo and offer valuable information for the development of durable disease resistance in rice through gene pyramiding and targeted breeding strategies.