Pathovars of Xanthomonas campestris Are Distinguishable by Restriction Fragment-Length Polymorphism

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Abstract
Cloned deoxyribonucleic acid (DNA) fragments, derived from a cosmid library of a Florida isolate of Xanthomonas campestris pv. citri 3041 were used to detect restriction fragment-length polymorphism among 93 strains of X. campestris, which make up 26 pathovars. DNA clones were radiolabeled and hybridized against Southern blot transfers of genomic DNAs of different strains of X. campestris digested with restriction endonucleases. Autoradiographs for DNA clones probed against genomic DNA revealed hybridization profiles which appeared to be highly conserved and unique for each pathovar tested. As a species, the population structure of X. campestris appeared basically clonal. Variability appeared to depend on the DNA probe used; some probes represented DNA loci which were highly variable, and some represented DNA loci which were highly conserved at the species level. By using more than one DNA probe, or by digesting the genomic DNAs with different restriction endonucleases, we were able to differentiate all of the strains of X. campestris described as belonging to a given pathovar. Differences among the pathovars were also confirmed by pathogenicity experiments on plants. Some phytopathogenic strains isolated from plants not previously described as susceptible to X. campestris could be grouped as being related to previously described pathovars.