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Auxin Production Is a Common Feature of Most Pathovars of Pseudomonas syringae

¹Institut des Sciences Végétales, Centre National de la Recherche Scientifique, Avenue de la Terrasse, F-91198 Gif sur Yvette Cedex; ²Station de Pathologie Végétale, Institut National de la Recherche Agronomique, 42, rue Georges Morel, B.P. 57, F-49071 Beaucouzé Cedex, France

We investigated indole-3-acetic acid (IAA) production by 57 pathovars of Pseudomonas syringae and related species. Most of those analyzed produced IAA, especially in the presence of tryptophan. Eight strains produced high IAA concentrations in the absence of Trp. The iaaM and iaaH genes of P. savastanoi pv. savastanoi were detected in a limited number of strains only, including the eight above-mentioned strains. Thus, IAA synthesis in most assayed strains of P. syringae and related species does not involve genes highly similar to iaaM and iaaH. In contrast, the iaaL gene encoding an IAA-lysine synthase was detected in most pathovars, and was often found on plasmids.

Additional keywords: Azospirillum, Erwinia, plant growth regulators, plant pathogens.