Indigenous Plasmids in Xanthomonas Campestris Pv. Pruni

Plasmid DNA of 60 strains of Xanthomonas campestris pv. pruni was isolated and analysed by electrophoresis in 0.7% agarose gel. All strains had plasmids and 10 size classes were identified. While 32 strains had only one plasmid, three strains had as many as four plasmids. A plasmid of 26.7 mdal, yielding similar size fragments upon restriction with EcoRI, SalI, BamHI, PstI, and HindIII, occurred most frequently (77% strains). Strains isolated from apricot, peach, plum, and sweet cherry had similar plasmid profiles. However, more than two plasmids in a single strain occurred only in strains isolated in southern New Jersey. There was no apparent relationship between presence of plasmids and pathogenicity on detached peach leaves. EcoRI restriction of plasmid DNA from 41 of 43 strains yielded common fragments of 13.6, 12.2, 7.3, 5.8, and 2.4 kb. These fragments may be epidemiologically significant.