Host range,RFLP, and antigenic relationships betweenRhizobium fredii strains andRhizobium sp. NGR234

Rhizobium fredii is a nitrogen-fixing symbiont from China that combines broad host range for nodulation of legume species with cultivar specificity for nodulation of soybean. We have compared 10R. fredii strains withRhizobium sp. NGR234, a well known broad host range strain from Papua New Guinea. NGR234 nodulated 16 of 18 tested lugume species, and nodules on 14 of the 16 fixed nitrogen. TheR. 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 byR. fredii were included within the host range of NGR234. Restriction fragment length polymorphisms (RFLPs) were detected with four DNA hybridization probes: the regulatory and commonnod genes,nodDABC; the soybean cultivar specificity gene,nolC; the nitrogenase structural genes, nifKDH; and RFRS1, a repetitive sequence fromR. fredii USDA257. A fifth locus, corresponding to a second set of soybean cultivar specificity genes,nolBTUVWX, was monomorphic. Using antisera against whole cells of threeR. fredii strains and NGR234, we separated the 11 strains into four serogroups. The anti-NGR234 sera reacted with a singleR. fredii strain, USDA191. Only one serogroup, which included USDA192, USDA201, USDA217, and USDA257, lacked cross reactivity with any of the others. Although genetic and phenotypic differences amongR. fredii strains were as great as those between NGR234 andR. fredii, our results confirm that NGR234 has a distinctly wider host range thanR. fredii.