Sinorhizobium frediiindigenous populations are prevalent in provinces of Central China whereasBradyrhizobiumspecies (Bradyrhizobium japonicum,B. diazoefficiens,B. elkanii, and others) are more abundant in northern and southern provinces. The symbiotic properties of different soybean rhizobia have been investigated with 40 different wild soybean (Glycine soja) accessions from China, Japan, Russia, and South Korea. Bradyrhizobial strains nodulated all the wild soybeans tested, albeit efficiency of nitrogen fixation varied considerably among accessions. The symbiotic capacity ofS. frediiHH103 with wild soybeans from Central China was clearly better than with the accessions found elsewhere.S. frediiNGR234, the rhizobial strain showing the broadest host range ever described, also formed nitrogen-fixing nodules with differentG. sojaaccessions from Central China. To our knowledge, this is the first report describing an effective symbiosis betweenS. frediiNGR234 andG. soja. Mobilization of theS. frediiHH103 symbiotic plasmid to a NGR234 pSym-cured derivative (strain NGR234C) yielded transconjugants that formed ineffective nodules withG. maxcv. Williams 82 andG. sojaaccession CH4. By contrast, transfer of the symbiotic plasmid pNGR234a to a pSym^-cured derivative ofS. frediiUSDA193 generated transconjugants that effectively nodulatedG. sojaaccession CH4 but failed to nodulate withG. maxcv. Williams 82. These results indicate that intra-specific transference of theS. frediisymbiotic plasmids generates new strains with unpredictable symbiotic properties, probably due to the occurrence of new combinations of symbiotic signals.