Assessment of biodiversity in rhizobia symbionts of common bean (Phaseolus vulgaris L.) in Santa Catarina, Brazil

Brazilian soils usually present a great number of populations of rhizobial bacteria capable of nodulating and fixing N-2 in symbiosis with common bean (Phaseolus vulgaris L.), but the diversity of these bacteria is still poorly known. This study aimed to assess the biodiversity of micro-symbionts of common bean in the state of Santa Catarina in southern Brazil. One-hundred and seventeen isolates were obtained from field-grown plants in 23 areas of the far west, midwest and southern plateau of Santa Catarina. Based on morphophysiological properties, the isolates were classified in nine groups. The DNA analysis by BOX-PCR, with the amplification of conserved and repetitive genome regions, detected 107 different profiles joined at a final similarity level of only 26.9 %, i.e., a high level of genetic diversity. The profiles obtained by the amplification of the 16S rRNA gene, followed by the digestion with three restriction enzymes (RFLP-PCR technique) defined six main groups and five isolated bacteria. The population consisted of 17.1 % Rhizobium tropici, 35.9 % R. etli, 32.5 % R. leguminosarum, 1.7 % R. giardinii and 12.8 % yet undocumented profiles of the common bean rhizobial species. R. tropici predominated in the acid soils of the midwest and southern plateau, R. leguminosarum was not detected in the far west and R. etli occurred in all three regions, while the last two species predominated in less acid soils. The results demonstrate the high inter- and intra-specific rhizobial diversity in the soils of Santa Catarina, besides indicating new species.