Isolation and characterization of the Rhizobium meliloti Tn5-mutants with impaired nodulation competitiveness

Two Tn5-mutants, T37 and T107, with decreased nodulation competitiveness (Cmp−) were isolated in Rhizobium meliloti strain CXM1-105. Their Cmp− phenotype was repeatedly displayed in sterile plant tests, where competitiveness was measured against a Fix− reference strain CXM1-48 and the parental strain CXM1-105. In addition mutant T37 showed a decreased nodulation rate (Nra−) at the early stages of alfalfa development (9–18 days after germination). Its mutant phenotype was demonstrated also under greenhouse conditions when it was evaluated against reference strain CXM1-48, and against indigenous rhizobial strains persisting in the soil.