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Genetics

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 (EC_z) occurred at frequencies of 10^–8 transconjugants per donor (TPD) or lower. However, transfer of RP1 from EC_z back to E. coli was more efficient at 10^–4 TPD. The transfer frequency of RP1 was not increased by mating a RP1-cured recipient EC_z with an E. coli donor bearing RP1, acquired conjugatively from the same EC_z transconjugant strain. Transconjugants of EC_z became resistant to carbenicillin, neomycin, and tetracycline as well as sensitive to lysis by plasmid-specific phages PRR1 and PRD1. Transconjugants of EC_z also retained the ability to cause stalk rot symptoms on maize. Intraspecific transfer of RP1 from EC_z to three of six strains of E. chrysanthemi isolated from hosts other than maize was detected at frequencies of 10^–8 to 10^–5 TPD. Interstrain transfer of RP1 to eight strains of EC_z was successful once at a frequency of 10^–8 TPD. Plasmid RP1 was transferred between mutants of a single EC_z strain at 10^–5 TPD in vitro and 10^–3 TPD in planta. Chromosomal transfer mediated by RP1 was detected in vitro among auxotrophic mutants of EC_z.