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Genetic Studies with Plasmid RP1 in Erwinia chrysanthemi Strains Pathogenic on Maize. G. H. Lacy, Assistant Plant Pathologist, Department of Botany and Plant Pathology, Connecticut Agricultural Experiment Station, New Haven, CT 06504; Phytopathology 68:1323-1330. Accepted for publication 3 March 1978. Copyright 1978 The American Phytopathological Society, 3340 Pilot Knob Road, St. Paul, MN 55121. All rights reserved.. DOI: 10.1094/Phyto-68-1323.

Transfer of the wide-host-range plasmid, RP1, from Escherichia coli into four of twelve Erwinia chrysanthemi strains isolated from stalk rot of maize (ECz) occurred at frequencies of 108 transconjugants per donor (TPD) or lower. However, transfer of RP1 from ECz back to E. coli was more efficient at 104 TPD. The transfer frequency of RP1 was not increased by mating a RP1-cured recipient ECz with an E. coli donor bearing RP1, acquired conjugatively from the same ECz transconjugant strain. Transconjugants of ECz became resistant to carbenicillin, neomycin, and tetracycline as well as sensitive to lysis by plasmid-specific phages PRR1 and PRD1. Transconjugants of ECz also retained the ability to cause stalk rot symptoms on maize. Intraspecific transfer of RP1 from ECz to three of six strains of E. chrysanthemi isolated from hosts other than maize was detected at frequencies of 108 to 105 TPD. Interstrain transfer of RP1 to eight strains of ECz was successful once at a frequency of 108 TPD. Plasmid RP1 was transferred between mutants of a single ECz strain at 105 TPD in vitro and 103 TPD in planta. Chromosomal transfer mediated by RP1 was detected in vitro among auxotrophic mutants of ECz.

Additional keywords: pathogenicity, in planta transfer, gene transfer, pseudotransconjugants.