Application of biofertilizer containing Bacillus pumillus TUAT1 on soybean without inhibiting infection by Bradyrhizobium diazoefficiens USDA110

Application of bio-fertilizer with the ability to promote root development in legume plants could be beneficial, and it is vital to find an inoculation method that does not inhibit symbiosis between rhizobium and plants. However, co-inoculation of rhizobia with different microorganisms on legumes generally inhibits interdependency with rhizobia. The present study was conducted to determine the ideal inoculation method of the bio-fertilizer ‘Yume-bio’ containing Bacillus pumilus TUAT1, which has plant growth-promoting activity, without inhibiting rhizobial infection of soybean. Soybean plants were inoculated with Bradyrhizobium diazoefficiens USDA110 during the time of sowing seeds. Then, two types of ‘Yume-bio’ applications were conducted: simultaneous inoculation with the rhizobia (SI) and 1 week after inoculation the rhizobia (I). No inoculation (NI) was used as the control. Four weeks after sowing, biomass dry weight (shoot and root) and nitrogenase activity based on acetylene reduction assay (ARA) both, per plant and nodule weight increased significantly in ‘I’ treatment compared to those in ‘NI.’ However, there were no significant differences between ‘SI’ and ‘NI’ for shoot biomass and ARA per plant. Nodule numbers decreased in ‘SI’ as compared to ‘NI,’ while they were not different between ‘I’ and ‘NI.’ This study suggests that simultaneous inoculation of ‘Yume-bio’ and rhizobia inhibits nodule development, while inoculation of ‘Yume-bio’ 1 week after inoculation of rhizobia is ideal for promoting soybean growth without inhibiting rhizobium infection in soybean.