Diverse <i>Bradyrhizobium</i> spp. with Similar Symbiosis Genes Nodulate Peanut in Different Regions of China: Characterization of Symbiovar sv. Arachis

A total of 219 rhizobial strains isolated from peanut grown in soils from six peanut croplands in Zhengyang county, Henan Province, were typed by PCR-RFLP of IGS sequences. Their phylogenetic relationships were refined on representative strains using sequence analyses of 16S rRNA genes, housekeeping genes (<i>atpD</i>, <i>recA</i>, <i>glnII</i>) and symbiosis genes (<i>nodA</i>, <i>nodC</i> and <i>nifH</i>). The 219 rhizobial isolates were classified into 13 IGS types, and twenty representatives were defined within eight <i>Bradyrhizobium</i> genospecies: <i>B. guangdongense</i> covering 5 IGS types (75.2% of total isolates), <i>B. guangzhouense</i> (2 IGS types, 2.7% total isolates), <i>B. zhengyangense</i> (1 IGS type, 11.3% total isolates) and five novel genospecies (5 IGS types, 0.9 to 3.2% total isolates). All representative strains had identical <i>nodA</i>, <i>nodC</i> and <i>nifH</i> sequences except for one <i>nifH</i> sequence. With this one exception, these sequences were identical to those of the type strains of <i>Bradyrhizobium</i> species and several <i>Bradyrhizobium</i> genospecies isolated from peanut in different regions of China. The <i>nodC</i> sequences of all strains showed < 67% similarity to the closest strains on the Genbank database indicating that they are representative of a novel <i>Bradyrhiobium</i> symbiovar. This study has shown that (1) diverse <i>Bradyrhizobium</i> spp. with similar symbiosis genes nodulate peanut in different regions of China. (2) Horizontal transfer of genes involved in nodulating peanut is common between <i>Bradyrhizobium</i> species in soils used to grow the crop in China. (3) The strains studied here are representative of a novel <i>Bradyrhizobium</i> symbiovar that nodulates peanut in China. We propose the name sv. arachis for this novel symbiovar indicating that the strains were isolated from <i>Arachis hypogaea</i>. Results here have practical implications in relation to the selection of rhizobial inoculants for peanut in China.