ABSTRACT
Twelve genotypes of soybean were examined for effectiveness of N2 fixing symbiosis with fast-and slow-growing soybean rhizobia in a greenhouse pot experiment. Plant introductions were inoculated with five fast-growing strains of rhizobium fredii [USDA HH003 HH103, HH303, 191 and 205] or six slow-growing strains of Bradyrhizobium japonicum [USDA 24, 31, 123 and mixed inoculum of USDA 6, 110 and 136]. Seven-week old plants were assessed for nodule dry weight, plant-top dry weight, and nitrogen accumulation. Statistical analyses showed that the combined genotype-stains effect was responsible for all the variation observed in all parameters. In general, the slow- growing strains formed effective nodules on all soybean genotypes, except strain USDA 24. The fast-growing rhizobia strains were less effective on most of soybean genotypes particularly strains USDA 191 and 205. There were significant differences in plant-top dry weight among the different soybean genotypes due to the interaction with the different strains of soybean rhizobia. The interaction between soybeen genotypes and the different strains revealed less top dry weight accumulation with strains USDA 191, 205 and 24. Among soybean genotypes, large differences were observed in N2 fixed due to the inoculation with the different R. japonicum strains. In same way, the same cultivar responded differently to the different strains. The high response of N2 fixation was obtained from the interaction between the cultivar Jupiter and the slow-growing Mix rhizobia strains [6, 110, and 136]