Impact of Inoculations with Indigenous Bradyrhizobium diazoefficiens Isolates on Productivity and Competition with Indigenous Bradyrhizobia in Adzuki Bean (Vigna angularis)

Abstract

We herein examined the inoculation effects of indigenous Bradyrhizobium diazoefficiens isolates on the growth and yield of adzuki beans and their competition with other bradyrhizobia using pot and field experiments. In the pot experiment, shoot nitrogen content was significantly higher following inoculations with AMP1 and Bd (a mixture of AN9 and AN20) than with the control. Furthermore, a correlation was observed between shoot nitrogen content and shoot dry weight. In the field experiment, the inoculating isolates did not significantly affect growth or yield. However, an interaction effect was observed in pod numbers and yield, suggesting that the effects of inoculation varied depending on the cultivar and inoculating isolate. In the correlation analysis, pod number correlated with node number and nodule number. Similarly, yield correlated with shoot length, node number, nodule number, and pod number. Regarding competition between inoculated isolates and other strains, B. elkanii was dominant in pot and field experiments. To enhance the yield of adzuki bean through inoculations, it is necessary to overcome competition from indigenous B. elkanii and increase the occupancy rate of B. diazoefficiens isolates.