Symbiotic matching, taxonomic position, and field assessment of symbiotically efficient rhizobia isolated from soybean root nodules in Sichuan, China

To find wide host range compatible potential inoculant strains with high efficiency in N fixation, we isolated rhizobia from soybean root nodules in Sichuan. Most of the isolated rhizobia were no- or low-effective strains. Eight out of 75 isolates promoted significantly the growth of soybean cultivar Gongxuan No. 1. When tested with three more soybean cultivars, the isolates assigned as Bradyrhizobium japonicum SCAUs36, Bradyrhizobium diazoefficiens SCAUs46, and Ensifer fredii SCAUs65 promoted significantly (P < 0.05) the growth of each cultivar. The nodC and nifH genes of bradyrhizobial SCAUs36 and SCAUd46 and E. fredii SCAUs65 grouped together with those of broad host range strains. In field experiments with two more soybean cultivars, B. diazoefficiens SCAUs46 and E. fredii SCAUs65 performed well both in mild and hot-dry climates, implying that the isolates were potential inoculants to be applied in diverse soil and climate conditions.