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Genetics

Plasmid pDC190: Distribution Among Erwinia stewartii Strains and Nonassociation with Virulence. R. D. Frederick, Research associate, Department of Plant Pathology, Ohio Agricultural Research and Development Center, The Ohio State University, Wooster 44691; D. L. Coplin, associate professor, Department of Plant Pathology, Ohio Agricultural Research and Development Center, The Ohio State University, Wooster 44691. Phytopathology 76:165-170. Accepted for publication 30 August 1985. Copyright 1986 The American Phytopathological Society. DOI: 10.1094/Phyto-76-165.

The correlation between the presence of pDC190 and the virulence of Erwinia stewartii to corn was investigated. Southern blot hybridizations with use of a pDC190::Mu pf7701 probe confirmed earlier observations that pDC190 replicons were present in all virulent strains. However, a virulent strain in which pDC190 had been labeled with Mu pf7701 was cured of the hybrid plasmid without affecting virulence. Furthermore, the virulence of DC336-1, a previously isolated mutant suspected of lacking pDC190 genes for virulence, was restored by a cloned chromosomal fragment. Therefore, even though highly conserved in E. stewartii, pDC190 does not appear to be essential for virulence on corn seedlings.