Summary: pv. is a bacterial pathogen of olive, oleander and privet, on which it induces tumorous overgrowths called knots or galls. Production of indoleacetic acid (IAA), a necessary factor for gall induction, is coded in oleander strain EW2009 by a 52 kb plasmid called pIAA1. To determine if this trait were commonly plasmid-borne in other strains of this pathogen, Iaa mutants were isolated from twelve different strains by selection for α-methyltryptophan resistance. Each mutant was compared in its plasmid pattern with the parent wild-type. In oleander strains PB205 and PB213 loss of IAA production was associated with loss of, or large deletions in, a 73 kb plasmid called pIAA2. In the remaining strains from olive and privet loss of IAA production was not accompanied by the loss of any plasmid. To prove that pIAA2 coded for the genes for IAA production, a radioactive probe containing the first gene of the IAA pathway () was hybridized to the plasmid DNA of the twelve strains. Only pIAA2 showed homology. We concluded that of all strains studied only PB205 and PB213 harboured a plasmid coding for IAA production, while in the remaining strains the IAA genes were located on the chromosome.


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