Plasmids in Pseudomonas syringae pv. pisi carry genes for pathogenicity

All strains tested which are pathogenic to peas and which react with antiserum to Pseudomonas syringae pv. pisi contain two to four plasmids; non-pathogens contain none. Two plasmids from a pathogenic strain were transferred individually to a non-pathogenic recipient strain of Pseudomonas syringae: both plasmids converted the recipient to a pathogen on peas and from hypersensitivity negative to hypersensitivity positive on tobacco. Neither plasmid encoded homoserine catabolism.