RESTRICTION-FRAGMENT-LENGTH-POLYMORPHISM ANALYSES OF THE PLASMID DNASIN STRAINS OF XANTHOMONAS-CAMPESTRIS PV VESICATORIA FROM DIFFERENT GEOGRAPHIC AREAS

Restriction fragment length polymorphisms (RFLPs) of plasmid DNAs in X anthomonas campestris pv. vesicatoria were analysed using 77 strains f rom the United States, Argentina, Australia, Taiwan, and Korea. One or more plasmids were detected in all tested strains, irrespective of ge ographic origin, host plant from which isolated, or chemical resistanc e. All Korean strains contained a few plasmids of similar high molecul ar weight, whereas some small plasmids occured only in strains from th e United States, Argentina, and Taiwan. After digesting total plasmid DNAs with each of four restriction endonucleases, 18 fragments with si zes from about 1 to 23 kb were visualized. Seventy-seven strains of di verse geographic origins, with different levels of resistance to strep tomycin and copper. were classified into the 14 RFLP groups based on t he restriction endonuclease digestion patterns of their plasmid DNAs. Strains belonging to each group shared DNA fragments of identical size , suggesting the possible presence of similar plasmids in these strain s. A 5.8-kb EcoRI plasmid DNA probe prepared from the United States st rain 81-23 hybridized to EcoRI plasmid digests from all tested strains . Other plasmid DNA fragments of the strain 81-23 used as probes had n o homology to plasmid DNA fragments from several strains around the wo rld. The variation in hybridization profiles of plasmid DNA was very s imilar to the results obtained by RFLP analysis of plasmid DNA digeste d by four restriction enzymes. Most of the Korean strains tested were highly sensitive to streptomycin and copper, whereas most strains from other geographic areas showed a high level of resistance to one or tw o of the chemicals. Cluster analysis of genetic distance between the s trains based on the data obtained generated the dendrograms that separ ated all Korean strains from the other strains, suggesting that plasmi d DNA of the Korean strains may be genetically very different from tho se of the others.