Increasing symbiotic nitrogen fixation in soybean by using mutation in microsymbiont Bradyrhizobium japonicum

To increase the symbioticnitrogen fixation in soybean, a native Bradyrhizobium japonicum strain RS 117 was selected from four strains via infectiveness, symbiotic effectiveness and sequancing 16S rRNA gene. Then, mentioned strain in the form of YMB inoculum wasirradiated by gamma rays dosages 0-5000 Gray with a 500 Gray interval dosage. About 800 mutant isolates were collected on YMA from different doses. 11 isolates in efficiency point of view changing the GMGT media colour were selected as the best isolates for further study. These isolates were tested for their symbiotic effectiveness (SE) under proper greenhouse condition with a randomized complete block design in 3 replications; and 3 more efficient isolates No. 3, 8 and 9  increased 56- 81 percent SE more than wild strain. At last, relative gene expersion nodA, nifK2 in mutant and wild strain bacteria approved mollacular differences between both of them by indicating Increase and decrease in amount, in mutant isolate number 9 in comparison with the wild Bradyrhizobium japonicum strain RS 117. The results indicate that gamma-irradiated mutations in Bradyrhizobium japonicum strains have significantly increased the biological fixation of nitrogen in soybean plants.