HOST-RANGE, RFLP, AND ANTIGENIC RELATIONSHIPS BETWEEN RHIZOBIUM-FREDII STRAINS AND RHIZOBIUM SP NGR234

Rhizobium fredii is a nitrogen-fixing symbiont from China that combine s broad host range for nodulation of legume species with cultivar spec ificity for nodulation of soybean. We have compared 10 R. fredii strai ns with Rhizobium sp. NGR234, a well known broad host range strain fro m Papua New Guinea. NGR234 nodulated 16 of 18 tested lugume species, a nd nodules on 14 of the 16 fixed nitrogen. The R. fredii strains were not distinguishable from one another. They nodulated 13 of the legumes , and in only nine cases were nodules effective. All legumes nodulated by R. fredii were included within the host range of NGR234. Restricti on fragment length polymorphisms (RFLPs) were detected with four DNA h ybridization probes: the regulatory and common nod genes, nodDABC; the soybean cultivar specificity gene, nolC; the nitrogenase structural g enes, nifKDH; and RFRS1, a repetitive sequence from R. fredii USDA257. A fifth locus, corresponding to a second set of soybean cultivar spec ificity genes, nolBTUVWX, was monomorphic. Using antisera against whol e cells of three R. fredii strains and NGR234, we separated the 11 str ains into four serogroups. The anti-NGR234 sera reacted with a single R. fredii strain, USDA191. Only one serogroup, which included USDA192, USDA201, USDA217, and USDA257, lacked cross reactivity with any of th e others. Although genetic and phenotypic differences among R. fredii strains were as great as those between NGR234 and R. fredii, our resul ts confirm that NGR234 has a distinctly wider host range than R. fredi i.