Diverse Peanut Bradyrhizobial Communities in Chinese Soils: Insights from Eastern, Central, and Northern Henan Province.

Henan province is a major peanut-producing area in China, but research on rhizobia nodulating peanut have been limited to southern Henan, which accounts for only less than half of the province. A collection of 212 strains of peanut rhizobia was obtained from six field sites in eastern, central, and northern Henan, Central China, by using peanut as a trap host under glasshouse conditions. PCR-RFLP analysis of ribosomal IGS sequences classified the 212 strains into 28 distinct types. Phylogenetic analyses of the 16S rRNA, atpD, gyrB, dnaK, and rpoB genes from 30 representative strains of the 28 IGS types identified revealed the presence of Bradyrhizobium. liaoningense, B. yuanmingense, B. zhengyangense, and two novel Bradyrhizobium genospecies. This composition differs from the peanut rhizobia community found in southern Henan. B. liaoningense was the dominant species, covering 49% of the total isolates across the field sites, while B. zhengyangense accounting for 27%, B. yuanmingense for 7% and the two novel Bradyrhizobium genospecies for 17%. Phylogenetic analysis showed that the symbiosis-related nodC and nifH gene sequences clustered into six groups: three associated exclusively with the peanut host (symbiovar arachidis and two unnamed group), three originating from other legume hosts (sv. glycinearum, cajani and retamae). Through the principal component analysis (PCA) between IGS types or species and soil physicochemical properties and environmental factors, it showed that IGS types 1, 3, 5, 8, 9, 12, 14, 15, 18, and 21 positively correlated with AveTmax, AveTmin, AN and AP. IGS types 4, 11, 16, 17, 20, 25, and 26 were positively associated with Alt, AvePrecp, and pH. IGS types 2, 7, 10, 22, 24, and 27 correlated with AP, while remaining types exhibited correlations with OM. In addition, B. yuanmingense, B. liaoningense, and Bradyrhizobium genosp. I positively affected by AveTmax, AP, AN, and AK. Bradyrhizobium genosp. II positively correlated with AK, AN, and OM while B. zhengyangense mainly affected by AvePrecp and pH. The alkaline soil pH in this study differs greatly from the acid soils in southern Henan, explaining the inconsistency between the species of peanut rhizobia detected in southern Henan and the rest of the province. The symbiotic effect assay demonstrated that all representative strains successfully formed nodules and exhibited a significant increase in symbiotic efficiency. Representative strains revealed diverse abiotic stress tolerance to NaCl, acidity, alkalinity, temperature and drought. It conducted a comprehensive collection of peanut rhizobia in eastern, central, and northern Henan province, identifying two putative novel Bradyrhizobium species and isolating rhizobial strains with high symbiotic efficiency and robust stress tolerance. This study is a necessary basic for the producing and application of peanut rhizobial inoculant in this main agricultural province.