Characterization of rhizobia isolates obtained from nodules of wild genotypes of common bean

This study aimed to evaluate the tolerance to salinity and temperature, the genetic diversity and the symbiotic efficiency of rhizobia isolates obtained from wild genotypes of common bean cultivated in soil samples from the States of Goiás, Minas Gerais and Paraná. The isolates were subjected to different NaCl concentrations (0%, 1%, 2%, 4% and 6%) at different temperatures (28 °C, 33 °C, 38 °C, 43 °C and 48 °C). Genotypic characterization was performed based on BOX-PCR, REP-PCR markers and 16S rRNA sequencing. An evaluation of symbiotic efficiency was carried out under greenhouse conditions in autoclaved Leonard jars. Among 98 isolates about 45% of them and Rhizobium freirei PRF81 showed a high tolerance to temperature, while 24 isolates and Rhizobium tropici CIAT899 were able to use all of the carbon sources studied. Clustering analysis based on the ability to use carbon sources and on the tolerance to salinity and temperature grouped 49 isolates, R. tropici CIAT899 and R. tropici H12 with a similarity level of 76%. Based on genotypic characterization, 65% of the isolates showed an approximately 66% similarity with R. tropici CIAT899 and R. tropici H12. About 20% of the isolates showed symbiotic efficiency similar to or better than the best Rhizobium reference strain (R. tropici CIAT899). Phylogenetic analysis of the 16S rRNA revealed that two efficient isolates (ALSG5A1 and JPrG6A8) belong to the group of strains used as commercial inoculant for common bean in Brazil and must be assayed in field experiments.