Synergistic interactions between Bradyrhizobium japonicum and the endophyte Stenotrophomonas rhizophila and their effects on growth, and nodulation of soybean under salt stress

Understanding the interactions between endophytic bacteria, rhizobia, free living root associated bacteria and their host plants under stressed conditions remains a significant challenge for proposing strategies to improve the efficacy of PGPR. In this study we analyzed the role of the endophytic bacterium Stenotrophomonas rhizophila in alleviating salinity stress in plants. The nodulation efficiency, plant growth, nitrogen and phosphorus uptake of soybean under hydroponic salt stress conditions were determined. Soybean seedlings were inoculated with Bradyrhizobium japonicum BDYD1 and S. rhizophila ep-17 were grown in hydroponic plastic pots containing 2 l of Hoagland solution for 42 days. Salinity conditions were established by adding 50 and 75 mM NaCl to the nutrient solution. The results showed that the salinity decreased the colonization of B. japonicum BDYD1 in the rhizosphere of soybean, inhibited shoot, root growth, and nodulation compared with those of unstressed plants. We found synergistic interactions between compatible salt tolerant S. rhizophila ep-17 and B. japonicum BDYD1 strains which were manifested themselves as improved root, shoot length, dry weight, N and P uptake and number of nodules compared with the uninoculated plants grown under 75 mM NaCl condition. S. rhizophila and Bradyrhizobium build beneficial association in the rhizosphere and can act synergistically on promoting plant growth, nutrient uptake and fitness of hydroponically grown soybean under salt stress condition.