Polyphasic characterization of rhizobia that nodulate Phaseolus vulgaris in West Africa (Senegal and Gambia)

Fifty-eight new isolates were obtained from root nodules of common bean (Ph aseolus vulgaris) cultivated in soils originating from different agroecolog ical areas in Senegal and Gambia (West Africa). A polyphasic approach inclu ding both phenotypic and genotypic techniques was used to study the diversi ty of the 58 Rhizobium isolates and to determine their taxonomic relationsh ips with reference strains. All the techniques performed, analysis of multi locus enzyme electrophoretic patterns, SDS-PACE profiles of total cell prot eins, PCR-RFLP analysis of the genes encoding 16S rRNA and of the 16S-23S R NA intergenic spacer region (ITS-PCR-RFLP), auxanographic tests using API g alleries and nodulation tests lead to the consensus conclusion that the new rhizobial isolates formed two main distinct groups, I and II. belonging to Rhizobium tropici type B and Rhizobium etli, respectively. By MLEE R. etli and group II strains showed several related electrophoretic types, evidenc ing some extent of internal heterogeneity among them. This heterogeneity wa s confirmed by other techniques (ITS-PCR-RFLP, SDS-PAGE and host-plant-spec ificity) with the same nine distinct strains of group II showing some diffe rences from the core of group II (54 strains).