Genetic diversity and distribution of bradyrhizobia nodulating peanut in acid-neutral soils in Guangdong Province

To reveal the genetic diversity and geographic distribution of peanut (Arachis hypogaea L.) rhizobia in Guangdong Province, one of the main peanut producing regions in China, 216 bradyrhizobial isolates were trapped by peanut plants inoculated with soil samples (pH 4.7–7.4) collected from ten sites in Guangdong. Based on BOX-PCR fingerprinting analysis, 71 representative isolates were selected for sequence analyses of ribosomal IGS, recA, atpD and symbiotic gene nodA. As a result, 22 genospecies were detected in the peanut rhizobia, including eight minor groups or single strains corresponding to Bradyrhizobium diazoefficiens, B. japonicum, B. yuanmingense, B. arachidis, B. guangdongense, B. guangxiense, B. iriomotense and B. liaoningense, as well as 14 novel Bradyrhizobium genospecies covering the majority of isolates. Five symbiotic clusters were obtained based on the phylogenetic relationships of nodA genes, related to the soybean-nodulating or peanut-nodulating reference strains. Biogeographic patterns, which were mainly correlated with potassium content and pH, were detected in the peanut bradyrhizobial community in Guangdong Province. These findings enriched the diversity of peanut rhizobia, and added the K content as a special determinant for peanut rhizobial distribution in acid soils.