Genetic diversity of Rhizobium present in nodules of Phaseolus vulgaris L. cultivated in two soils of the central region in Chile

Although Phaseolus vulgaris L. is native from the Americas and is currently cultured in diverse areas, very little is known about the diversity of symbiotic nitrogen fixing Rhizobium (mycrosymbiont) in many of those cultures. Therefore, the aim of this study was to assess the genetic diversity of Rhizobium present in nodules of P. vulgaris in the central region of Chile. A method to extract DNA from surface-sterilized nodules was applied to two populations of the same seed variety grown in different fields. The 16S rRNA and nifH genes were amplified directly from the DNA extracted. DGGE analysis and clone libraries showed a restricted genetic diversity of the microsymbiotic populations that nodulate P. vulgaris. Both molecular markers revealed the presence of a microsymbiont closely related to Rhizobium etli in all the plants from the soils studied, indicating that the populations of Rhizobium sp. nodulating P. vulgaris in the central region of Chile displayed an extremely low genetic diversity. The level of genetic diversity in microsymbiont populations in plants grown in soils with different origin suggested that other factors rather than the indigenous soil rhizobial populations play a major role in the selection of the symbiotic partner in P. vulgaris.