Differentiation of Pseudomonas syringae subsp. savastanoi strains isolated from various host plants by restriction fragment length polymorphisms.

A 1.8 kb DNA fragment encoding a putative protein similar to precorrin-3 methylase, a protein of Pseudomonas aeruginosa involved in cobalamin biosynthesis, was cloned from an olive strain of the plant pathogenic bacterium Pseudomonas syringae subsp. savastanoi. This fragment, potentially involved also in virulence, methionine prototrophy and ability to elicit a hypersensitive response, was used as a probe for detecting restriction fragment length polymorphism (RFLP) in 52 strains of P. s. subsp. savastanoi isolated from olive, oleander and ash. Southern blot analysis revealed a single strongly hybridizing band in all P. s. subsp. savastanoi strains and EcoRI polymorphism was detected among strains isolated from olive plants. In addition, when HindIII was used as a restriction enzyme, the P. s. subsp. savastanoi strains isolated from olive clearly differed from those isolated from oleander and ash on the basis of the size of a single hybridizing band. This clear difference between the strains isolated from olive and those isolated from oleander further supports the hypothesis that the populations of P. s. subsp. savastanoi which infect the above-mentioned host plants differ from one another.