Abstract

This study was conducted to evaluate the possibility of increasing Bradyrhizobium efficiency in fixing biological nitrogen in soil. Bradyrhizobium isolates were obtained from cowpea field in certain Iraqi provinces. Isolates were purified, propagated and authenticated. Isolates were then subjected to a range of Gamma ray dose of irradiation of 0 to 800Gy. For all isolates number of nodules formed by all isolates increased with the increase of Irradiation dose to 400Gy after which numbers of nodules of all isolates were markedly reduced. Highest nodules numbers of all isolates were observed under 400GY irradiation dose. Under the same irradiation dose of 400GY numbers of nodules differ with different isolates being the highest under isolate No. 2.