Genetic specificity of nodulation

Summary A genetic system is proposed for establishing desirable strains of Rhizobium japonicum in soybean fields against the competition of aggressive but less productive indigenous strains. This system requires soybean cultivars which substantially exclude the indigenous strains while selectively admitting specific introduced strains. Rhizobium strains were identified which were infective, both in sand and in soil culture, with a host genotype (rj₁rj₁) which excludes most indigenous strains. Rhizobium infectivity was associated, for the first time, with the propensity to induce symptoms caused by rhizobitoxine production by the bacteria. The basis of this association is unknown. A possible enabling role for rhizobitoxine, or a precursor or derivative of rhizobitoxine, in the infection process is discussed.