Pathogenic and Genetic Diversity in Asian Strains of Xanthomonas oryzae pv. oryzae

The 57 strains of Xanthomonas oryzae pv. oryzae (Xoo) collected from rice growing countries of India, Indonesia, Malaysia, Thai, Taiwan and Philippines were characterized by using polymerase chain reac- tion fingerprinting and virulence analysis. The strains of Xoo were grouped into 13 races on the basis of their pathogenicity to international differential lines. Distribution of races was quite specific to the country. Three strains from India and two strains from Indonesia were virulent to cultivars containing the bacterial blight resistance gene xa5, while most strains from other countries were avirulent to xa5. The strains from India showed high virulence and broad range of pathogenicity, in contrast to those from Malaysia. Two vari- eties of containing Xa21 and xa5 gene, respectively, were resistant to almost Asian Xoo strains. Our Xoo collections from Asian countries were also divided into 4 genetic groups by clustering statistics on the basis of the results from PCR-based RFLP with IS1112 primers. A partial relationship was found among the genetic groups, countries and races, suggesting that strategies that target regional resistance breeding and gene deployment are feasible. The results of this study will facilitate the further understanding of the popu- lation structure of Xoo in Asia.