Difference of infectivity between two similar soybean rhizobial strains and immunohistochemical evidence of double infection

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Abstract
Two strains of soybean rhizobia (Bradyrhizobium japonicum OUG 115 and OUG 117), which were very similar in their microbiological properties but not in their imrnunological response, were tested for nodulation of Glycine max. Strain-specific antisera were obtained by adsorbing the antisera with the cross-reactive cellular antigen. The strains in the nodules formed were identified by cross agglutination and fluorescent immunohistochemical (FIHC) methods using the antibodies labeled with fluorescein isothiocyanate (FITC). Microscopic observation revealed clearly the difference of infectivity between the two strains. About 80 and 7.5% of the nodules tested were found to contain one strain, OUG 117 or OUG 115, respectively, and doubly infected nodules were estimated at 13%, when soybean was inoculated with the same concentration of the two strains.