Intra- and inter-specific competition in Rhizobium fredii and Bradyrhizobium japonicum as indigenous and introduced organisms

Schmidt 1973; Kapusta and Rouwenhorst 1973; Weaver and Frederick 1974). However, the numbers needed to overcome indigenous rhizobia are in many cases too excessive to be practical. In much of the soybean-growing area in the north central United States, an area encompassing many soil types, indigeneous strains of Bradyrhizobium japonicum serogroup 123 dominate nodulation of soybeans (Damirgi et al. 1967; Ham et al. 1971b). Although several factors have been examined to account for the success of serogroup 123 (Ham 1980), strain characteristics that confer competitive advantage to 123 remain unknown. The competitive success of 123 was found to be unrelated to an ability to outgrow other indigenous B. japonicum in the host rhizosphere (Moawad et al. 1984). Also, when competition studies were carried out in sterile vermiculite or in soils devoid of naturalized B. japonicum, an isolate of 123 from a midwestern soil was found to be a poor competitor (Kosslak 990