The family Rhizobiaceae consists of a heterogeneous group of Gramnegative, aerobic, non-spore-forming rods that can invade and form nodules on the root and, in some instances, on the stem of leguminous plants. The slow-growing nodulation bacteria which have specific association with soybean are referred to as Bradyrhizobium. Currentry, Bradyrhizobium has only one designated species. B. japonicum. Some soybean roots can also nodulate with a fast grower named Rhizobium fredii (Sprent and Sprent 1990)