AUTHOR=Tang Mingxing , Wang Haoyu , Qi Xin , He Teng , Zhang Bin , Wang Entao , Yu Miao , Wang Beinan , Wang Fang , Liu Zhongkuan , Liu Xiaoyun 

TITLE=Diversification of Sinorhizobium populations associated with Medicago polymorpha and Medicago lupulina in purple soil of China

JOURNAL=Frontiers in Microbiology

VOLUME=13

YEAR=2023

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2022.1055694

DOI=10.3389/fmicb.2022.1055694

ISSN=1664-302X

ABSTRACT=<p>The double selection of environment adaptation and host specificity forced the diversification of rhizobia in nature. In the tropical region of China, <italic>Medicago polymorpha</italic> and <italic>Medicago lupulina</italic> are widely distributed, particularly in purple soil. However, the local distribution and diversity of rhizobia associated with these legumes has not been systematically investigated. To this end, root nodules of <italic>M. polymorpha</italic> and <italic>M. lupulina</italic> grown in purple soil at seven locations in Yunnan Province of China were collected for rhizobial isolation. The obtained rhizobia were characterized by RFLP of 16S–23S rRNA intergenic spacer, BOXAIR fingerprinting, and phylogeny of housekeeping and symbiosis genes. As result, a total of 91 rhizobial strains were classified into species <italic>Sinorhizobium medicae</italic> and <italic>S. meliloti</italic>, while three <italic>nodC</italic> gene types were identified among them. <italic>S. medicae</italic> containing <italic>nodC</italic> of type I was dominant in farmlands associated with <italic>M. polymorpha</italic>; while <italic>S. meliloti</italic> harboring <italic>nodC</italic> of type III was dominant in wild land nodulated by <italic>M. lupulina</italic>. For both rhizobial species, greater genetic diversity was detected in the populations isolated from their preferred host plant. A high level of genetic differentiation was observed between the two <italic>Sinorhizobium</italic> species, and gene flow was evident within the populations of the same species derived from different soil types, indicating that rhizobial evolution is likely associated with the soil features. To examine the effects of environmental features on rhizobial distribution, soil physicochemical traits and rhizobial genotypes were applied for constrained analysis of principle coordinates, which demonstrated that soil features like pH, nitrogen and sodium were the principle factors governing the rhizobial geographical distribution. Altogether, both <italic>S. medicae</italic> and <italic>S. meliloti</italic> strains could naturally nodulate with <italic>M. polymorpha</italic> and <italic>M. lupulina</italic>, but the rhizobium-legume symbiosis compatibility determined by both the host species and soil factors was also highlighted.</p>