TRANSFER FROM ERWINIA-HERBICOLA TO ESCHERICHIA-COLI OF A PLASMID ASSOCIATED WITH BIOCONTROL OF FIRE BLIGHT

Strains of Erwinia herbicola effective in the biocontrol of fire bligh t of hawthorn were used to investigate the possibility that the antago nistic activity is coded by plasmid-born genes. Agarose gel electropho resis of isolated plasmids from four antagonistic Erw. herbicola strai ns showed a band of a supercoiled 12 kb plasmid in each strain, with a second band greater than 16.2 kb consistently seen in two strains. Er w. herbicola strains showed resistance to penicillin-G, which could be conferred on penicillin-G sensitive Escherichia coli TG1 by transform ation with a pure Erw. herbicola plasmid preparation. Transformed stra ins of Esc. coli appeared to contain the Enu. herbicola 12 kb plasmid, but not the > 16.2 kb plasmid. In an agar plate assay, Esc. coli tran sformants produced an inhibition zone against Erw. amylovora similar t o those produced by the original Erw. herbicola strains. In two biocon trol assays, the transformed Esc. coli strains had a suppressive effec t on disease development on infected pear fruit slices and hawthorn bl ossoms.