DNA Homologies between Rhizobium fredii, Rhizobia That Nodulate Galega sp., and Other Rhizobium and Bradyrhizobium Species

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Abstract
The relationships between Rhizobium fredii and the rhizobia that nodulate Galega officinalis and Galega orientalis (goat''s rue) and recognized species of Rhizobium and Bradyrhizobium were investigated by using deoxyribonucleic acid (DNA)-DNA hybridization, legume nodulation tests, and phage typing. The R. fredii strains formed a distinct DNA homology group which could be divided into two subgroups. The mean levels of relative homology at 65.degree. C of 11 strains of R. fredii with R. fredii reference strains USDA 208 and USDA 191 were 86 and 80%, respectively. These values were significantly higher (Student''s t test, P < 0.001) than the mean levels of relative homology with DNAs from other groups of rhizobia. The Galega-nodulating rhizobia also formed a distinct DNA homology group. The mean levels of relative homology at 65.degree. C of DNAs from 11 strains with DNAs from reference strains gal1 and galNW3, which effectively nodulate G. officinalis, were 79 and 85%, respectively. These values were also significantly higher (Student''s t test, P < 0.001) than the values obtained with DNAs from other groups of rhizobia. These results correlated with cross-inoculation and phage-typing results and indicated that the two groups are genetically distinct. Genomic DNA was used as a probe in a modified colony hybridization autoradiographic procedure for the identification of DNAs from Rhizobium leguminosarum, R. fredii, and Rhizobium sp. (Galega) in colonies and from nodules.