GENETIC DIVERSITY OF XANTHOMONAS-ORYZAE PV ORYZAE IN ASIA

Restriction fragment length polymorphism and virulence analyses were u sed to evaluate the population structure of Xanthomonas oryzae pv, ory zae, the rice bacterial blight pathogen, from several rice growing cou ntries in Asia, Two DNA sequences from X. oryzae pv. oryzae, IS1112, a n insertion sequence, and avrXa10, a member of a family of avirulence genes, were used as probes to analyze the genomes of 308 strains of X. oryzae pv, oryzae collected from China, India, Indonesia, Korea, Mala ysia, Nepal, and the Philippines. On the basis of the consensus of thr ee clustering statistics, the collection formed five clusters. Genetic distances within the five clusters ranged from 0.16 to 0.51, and dist ances between clusters ranged from 0.48 to 0.64, Three of the five clu sters consisted of strains from a single country. Strains within two c lusters, however, were found in more than one country, suggesting patt erns of movement of the pathogen. The pathotype of X. oryzae pv. oryza e was determined for 226 strains by inoculating five rice differential cultivars. More than one pathotype was associated with each cluster; however, some pathotypes were associated with only one cluster. Most s trains from South Asia (Nepal and India) were virulent to cultivars co ntaining the bacterial blight resistance gene xa-5, while most strains from other countries were avirulent to xa-5. The regional differentia tion of clusters of X. oryzae pv. oryzae in Asia and the association o f some pathotypes of X. oryzae pv, oryzae with single clusters suggest ed that strategies that target regional resistance breeding and gene d eployment are feasible.