DISTRIBUTION OF XANTHOMONAS-ORYZAE PV. ORYZAE DNA MODIFICATION SYSTEMS IN ASIA

The presence or absence of two DNA modification systems, XorI and XorI I, in 195 strains of Xanthomonas oryzae pv. oryzae collected from diff erent major rice-growing countries of Asia was assessed. All four poss ible phenotypes (XorI(+) XorII(+), XorI(+) XorII(-), XorI(-) XorII(+) and XorI(-) XorII(-)) were detected in the population at a ratio of ap proximately 1:2:2:2. The XorI(+) XorII(+) and XorI(-) XorII(+) phenoty pes were observed predominantly in strains from southeast Asia (Philip pines, Malaysia, and Indonesia), whereas strains with the phenotypes X orI(-) XorII(-) and XorI(+) XorII(-) were distributed in south Asia (I ndia and Nepal) and northeast Asia (China, Korea, and Japan), respecti vely. Based on the prevalence and geographic distribution of the XorI and XorII systems, we suggest that the XorI modification system origin ated in northeast Asia and was later introduced to southeast Asia, whi le the XorII system originated in southeast Asia and moved to northeas t Asia and south Asia. Genomic DNA from all tested strains of X. oryza e pv, oryzae that were resistant to digestion by endonuclease XorII or its isoschizomer PvuI also hybridized with a 7.0-kb clone that contai ned the XorII modification system, whereas strains that were digested by XorII or PvuI lacked DNA that hybridized with the clone. Size polym orphisms were observed in fragments that hybridized with the 7.0-kb cl one. However, a single hybridization pattern generally was found in Xo rII(+) strains within a country, indicating clonal maintenance of the XorII methyltransferase gene locus, The locus was monomorphic for X. o ryzae pv. oryzae strains from the Philippines and all strains from Ind onesia and Korea.