Abstract

• Enhancement of legume nitrogen fixation by co-inoculation of plant-growth-promoting rhizobacteria (PGPR) with rhizobia is an alternative way to improve the availability of nitrogen in a sustainable agricultural system. This study was conducted to evaluate the co-inoculation effect of Bacillus pumilus TUAT1 and Bradyrhizobium japonicum USDA110 on soybean (Glycine max L.) cv. Enrei by using the plant box experiment and examined the growth parameters (plant weight, root weight, nodules number and nodule weight). The experiment was performed in the Plant Microbiology Laboratory, Department of International Environmental and Agricultural Science, Tokyo University of Agriculture and Technology, Japan in 2018. The growth parameters were measured after 15 days, and 30 days of inoculation period and the results indicated an increase number for all parameters in the dual inoculation than the single inoculation. The plants inoculated with B. pumilus TUAT1, B. japonicum USDA110 and co-inoculation (TUAT1 + USDA110) promoted the plant weight and root weight of soybean compared to un-inoculated plants in both inoculation periods. The nodule formation was not observed in the plants inoculated with B. pumilus TUAT1 alone and un-inoculated (control) at 15 days post inoculation, when co-inoculated and USDA110 inoculated plants provided the highest number of nodules and nodules weight after 30 days. The results proved the potential benefits of increasing nodulation and promoting plant growth through the synergetic effect of TUAT1 and USDA110.