STRAINS OF RHIZOBIUM-FREDII EFFECTIVELY NODULATE AND EFFICIENTLY FIX NITROGEN WITH MEDICAGO-SATIVA AND GLYCINE-MAX

Effective nodulation of and efficient symbiotic nitrogen fixation with alfalfa by strains of Rhizobium fredii, the fast-growing soybean micr osymbiont, is herein reported. This discovery has broad implications f or host specificity research and strain improvement. Effective nodulat ion of Egyptian alfalfa cultivar 'Giza 4' by R. fredii type strain USD A 205 was observed and deemed anomalous yet intriguing since nodulatio n of alfalfa by R. fredii had not been previously reported. To investi gate this anomaly, twenty-two strains of R. fredii, including the elev en strains first isolated fifteen years ago from east central province s of China, and three strains of R. meliloti were evaluated for symbio tic capabilities with 'ARC' alfalfa, a standard improved cultivar of M edicago sativa. Efficient nitrogen-fixing symbioses were formed by R. fuedii USDA strains 201, 208, 209 and 214 with this cultivar and four other USDA strains of R. fredii, including the type strain USDA 205, f ormed inefficient nodules. The former strains produced high nodule num bers and high plant dry weights under conditions of nil combined nitro gen, and strains 201, 208 and 214 exhibited symbiotic nitrogen fixatio n activities comparable to those of strains of R. meliloti, the long-r ecognized nitrogen-fixing microsymbiont of alfalfa. R. fiedii strains efficiently nodulating both soybean and alfalfa were confirmed by mega plasmid DNA content, by reinfection of both hosts, and by DNA RFLP.