PHYLOGENETIC-RELATIONSHIPS AMONG RHIZOBIUM SPECIES NODULATING THE COMMON BEAN (PHASEOLUS-VULGARIS L)

The phylogenetic relationships among Rhizobium species that nodulate P haseolus vulgaris (common bean) were determined by directly sequencing the amplified 16S ribosomal DNA genes of these organisms, The bean st rains formed four separate clusters, One cluster was composed of Rhizo bium leguminosarum by. trifolii, R, leguminosarum bv. viciae, and R, l eguminosarum bv, phaseoli, Two other clusters comprised Rhizobium etli and Rhizobium tropici, and the fourth cluster contained a single bean -nodulating strain, Data for species identification were obtained from DNA-DNA reassociation experiments, The levels of DNA relatedness amon g strains belonging to the three biovars of R. leguminosarum ranged fr om 58 to 67%, The levels of DNA relatedness between R, leguminosarum b v. phaseoli and R, etli and R. tropici ranged from 43 to 45% and 13 to 16%, respectively, The levels of DNA relatedness between the strain b elonging to the fourth cluster and strains of the other three Rhizobiu m species that nodulate beans were less than 10%.