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Molecular Plant Pathology

Phylogenetic Evidence for a Diversification of Pseudomonas syringae pv. pisi Race 4 Strains into Two Distinct Lineages. B. Cournoyer, Department of Biological Sciences, University of the West of England, Bristol BS16 1QY, United Kingdom; Current address: Université Blaise Pascal—Clermont—Ferrand II, URA CNRS 1940—BIOMOVE, 63 177 Aubière, France.; D. Arnold, R. Jackson, and A. Vivian. Department of Biological Sciences, University of the West of England, Bristol BS16 1QY, United Kingdom. Phytopathology 86:1051-1056. Accepted for publication 19 June 1996. Copyright 1996 The American Phytopathological Society. DOI: 10.1094/Phyto-86-1051.

The emergence of race variants among Pseudomonas syringae pv. pisi was investigated. P. syringae pv. pisi hrpL, intergenic sequences between hrpKL and hrpJL, and partial hrpK DNA sequences were used to establish the origin of a race 4-like derivative (PT10) obtained as an IncP1 plasmid transconjugant from a race 6 strain (1704B). DNA sequence comparisons of the hrpJKL region from these two strains show 10 substitutions, including silent and nonsilent substitutions in hrpL, and others in intergenic regions. Phylogenetic analysis of these sequences (DNA and deduced amino acids), including homologs from other P. syringae pathovars, group the lineages corresponding to the P. syringae pv. pisi sequences and cluster them with the P. syringae pv. syringae sequence outside a cluster corresponding to the P. syringae pv. phaseolicola/P. syringae pv. morsprunorum sequences. The race 4 derivative (PT10) is part of a lineage different from the race 6 strain. A hrpJKL polymerase chain reaction/restriction fragment length polymorphism method was used to identify environmental strains that correspond to the PT10 race 4-like population. Phylogenetic analysis including partial hrpL sequences from the race 4-type strain (895A), the race 4-like seed strains, and all the other P. syringae homologous sequences available show a divergence of the race 4 strains into two distinct lineages: a type-strain lineage and a PT10-like lineage.