Relatedness of Strains of Xanthomonas fragariae by Restriction Fragment Length Polymorphism, DNA-DNA Reassociation, and Fatty Acid Analyses

The levels of relatedness of strains of Xanthomonas fragariae collected over several years from locations in Canada and the United States were compared by determining fatty acid methyl ester profiles, restriction fragment length polymorphisms (RFLP) based on pulsed-field gel electrophoresis (PFGE) analysis, and DNA-DNA reassociation values. Based on qualitative and quantitative differences in fatty acid profiles, the strains were divided into nine groups and four groups by the MIDI “10% rule” and unweighted pair analysis, respectively. Restriction analysis of genomic DNA by PFGE with two endonucleases (XbaI and SpeI) revealed four distinct profiles. When a third endonuclease (VspI) was used, one group was divided into three subgroups. The profile of the American Type Culture Collection type strain differed from the profile of every other strain of X. fragariae. Considerable diversity was observed within X. fragariae, although the majority of the strains represented a clonal population. The four groups based on fatty acid profiles were similar to the four groups based on RFLP, but neither method related groups to the geographic origins of the strains. The DNA-DNA reassociation values were high for representative strains, providing evidence that all of the strains belong to the same species.