Use of the gusA gene marker in a competition study of the Rhizobium strains nodulating the common bean (Phaseolus vulgaris) in Senegal soils

Indigenous rhizobial population is among the factors which influence increa sed crop yield through inoculation with elite strains. In this study, we co mpared in greenhouse conditions the competitiveness of Rhizobium strain ISR A 355 for nodulation of the common bean (Phaseolus vulgaris) cultivated in different unsterile Senegal soils in terms of pH, N and C contents. The str ain ISRA 355 produced a stable GUS+ transconjugant which was used for compe tition with indigenous soil rhizobia in six localities. At Bayakh, the tran sconjugant ISRA 355gusA was less competitive than the indigenous rhizobial strains, whereas in the other localities, it was more competitive since it occupied more than 90% of the nodules. Thus the Rhizobium strain ISRA 355 s hould be used for successfully inoculating the common bean in Senegal soils .