Soil and climatic conditions determine the rhizobia in association with Phaseolus vulgaris in southern Brazil.

The common bean (Phaseolus vulgaris L.) plays a significant economic and social role in Brazil. However, the national average yield remains relatively low, largely because most bean cultivation is undertaken by small-scale farmers. In this context, biological nitrogen fixation (BNF) is an effective strategy for improving crop yield. Therefore, it is important to identify novel rhizobial strains well suited to local climatic conditions. This study used Phaseolus vulgaris as a trap plant in soils from three distinct conservation areas (Ponta Grossa, Ortigueira, and Londrina) within Paraná State, Brazil. The soil chemical analysis revealed that the pH values in the Ponta Grossa and Ortigueira regions were low, whereas the Ortigueira region exhibited elevated aluminum levels. A total of 94 strains were obtained from the nodules of plants and subjected to analysis for their morphological and genetic properties. No nodules were observed in the Ortigueira region. In the Ponta Grossa region, most of the strains were identified as belonging to the genus Paraburkholderia, whereas all strains from Londrina were identified as Rhizobium. The 16S rRNA gene phylogenetic analysis revealed a high degree of genetic similarity between the Paraburkholderia and Rhizobium strains. These findings indicate that soil chemical properties (pH and aluminum level) and climate conditions may have a significant impact on the symbiotic association between rhizobia and common bean.