DIVERSITY OF PLASMIDS IN XANTHOMONAS-CAMPESTRIS PV VESICATORIA

Plasmid profiles were determined for 522 strains of Xanthomonas campes tris pv. vesicatoria, the causal agent of bacterial spot of tomato (Ly copersicon esculentum) and pepper (Capsicum annuum). The numbers and s izes of plasmids in strains from culture collections, as well as in st rains recently isolated from plants in commercial fields of pepper or tomato, were diverse. Each plasmid was placed into one of 13 classes b ased on size, as determined by electrophoretic mobility in agarose gel s. Plasmid sizes ranged from about 3 to 300 kb. Ten strains had no det ectable plasmid. Seventy-one different plasmid profiles were observed, with a maximum of five plasmid size classes in a profile. No plasmid or plasmid profile was characteristic for X. campestris pv. vesicatori a. Mobility of plasmids was demonstrated in field experiments after in oculation of pepper plants with donor strains containing plasmids in f ive classes and an antibiotic-resistant recipient strain that containe d one unique plasmid. All strains recovered on an antibiotic-amended m edium contained the unique plasmid present in the recipient strain. Tw enty-nine percent of the 199 cultures recovered on the antibiotic-amen ded medium in one experiment contained one or more plasmids that were similar in size to those in the donor strains; seven different plasmid profiles were observed. The diverse plasmid content of strains of X. campestris pv. vesicatoria in nature may be the result of frequent tra nsfer of the plasmids between strains.