POPULATION DIVERSITY OF PSEUDOMONAS-SYRINGAE SUBSP, SAVASTANOI ON OLIVE AND OLEANDER

Twenty-one strains of Pseudomonas syringae subsp. savastanoi, isolated from knots on olive and oleander trees growing in close proximity to or in physical contact with one another, were evaluated for knot induc tion and for bacteriocin production. In addition, DNA preparations fro m the bacterial strains were tested for hybridization to probes contai ning the tryptophan monooxygenase (iaaM) and isopentenyl transferase ( ipt) genes, which are involved in indole-3-acetic acid and cytokinin b iosynthesis, respectively, in P.s. subsp, savastanoi. The strains show ed features characteristic of strains usually isolated from their resp ective host plants. For example, all 10 oleander strains were virulent both to oleander and olive, did not produce bacteriocins and harboure d the iaaM gene on plasmids. In contrast, all 11 olive strains were vi rulent only to olive, 10 strains produced bacteriocins, and nine strai ns carried the iaaM gene on the chromosome. Two olive strains (OA11. O D21) harboured the gene coding for iaaM on plasmids. Furthermore, stra in OD21 carried the iaaM gene on the same plasmid as the ipt gene. Thi s is the first report both of a plasmid-borne iaaM in typical olive st rains (virulent only to olive and bacteriocin producers), and of the p resence of the ipt gene on the same plasmid, In olive and oleander str ains the ipt gene was located either on plasmids or on the chromosome, These results suggest that under natural conditions the pathogen does not appear to spread from oleander to olive even when trees are growi ng in close proximity or in physical contact. The location of the phyt ohormone genes on plasmids or on the chromosome is discussed in relati onship to bacteriocin-production and knot-induction on the host specie s.