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Genetic Variation in Strains of Clavibacter michiganense subsp. sepedonicum: Polymorphisms in Restriction Fragments Containing a Highly Repeated Sequence. Bradley D. Mogen, Department of Plant Pathology, North Dakota State University, Fargo 58105; Hope R. Olson(2), Robert B. Sparks(3), Neil C. Gudmestad(4), and Arland E. Oleson(5). (2)(3)(5)Department of Biochemistry, North Dakota State University, Fargo 58105; (4)Department of Plant Pathology, North Dakota State University, Fargo 58105 Phytopathology 80:90-96. Accepted for publication 2 August 1989. Copyright 1990 The American Phytopathological Society. DOI: 10.1094/Phyto-80-90.

Plasmid pCS1, a widely distributed plasmid in the potato pathogen Clavibacter michiganense subsp. sepedonicum, contains two copies of a 1.3-kilobase repeated sequence that is present in high copy number on the bacterial chromosome. A BamHI restriction fragment containing one of the plasmid copies of the repeated sequence has been cloned into transcription vector pGEM4. The transcript of this cloned fragment has been used as a molecular probe to detect polymorphisms in restriction fragments that contain the repeated sequence. Eleven different restriction enzymes were used to generate restriction fragment length polymorphism (RFLP) patterns from chromosomal DNA of 10 strains of the bacterium. Under the conditions employed in this study, restriction enzymes BamHI, BclI, BstXI, and SmaI were particularly effective in yielding RFLP patterns that permit discrimination of strains. Restriction enzyme NheI was useful for differentiating pathogen strains that contain autonomously replicating pCS1 from those in which the plasmid is integrated into the bacterial chromosome. The RFLP patterns produced by NheI also provided evidence that integration of pCS1 into the chromosome is a site-specific process. No alterations in RFLP patterns were observed upon repeated subculture of selected strains. Numerical analysis of the RFLP data indicated that the strains are of high similarity.

Additional keywords: potato bacterial ring rot, Solanum tuberosum.