SYMBIOTIC EFFECTIVENESS OF BRADYRHIZOBIUM JAPONICUM USDA 110 AND SINORHIZOBIUM FREDII USDA 191 ON TWO DIFFERENT SOYBEAN CULTIVARS

Abstract

Green house experiments were conducted to investigate the symbioticeffectiveness of two bacteria that fix nitrogen to soybeans: Slow growingbacteria (Bradyrhizobium japonicum USDA 110) and fast growing bacteria(Sinorhizobium fredii USDA 191). Two varieties of soybeans were used:Gazelle (non promiscuous variety) and TGx 1740 (promiscuous variety). Theexperimental design was a randomized complete design arrangementreplicated four times. Nodulation, acetylene reduction activity and dry matteraccumulation by nodulated plants growing in a nitrogen-free culture systemwere used to compare the symbiotic effectiveness of the fast-growingSinorhizobium fredii USDA 191 with that of the slow-growingBradyrhizobium japonicum USDA 110 in symbiosis with two soybean(Glycine max (L.) Merr.) Cultivars. Measurement of the amount of nitrogenaccumulated 30 day period of vegetative growth showed that Sinorhizobiumfredii was more effective in nitrogen fixation in TGX variety than in Gazellevariety while Bradyrhizobium japonicum was more effective in Gazellevariety than in TGx. The superior N2 fixation capability of Sinorhizobiumfredii with TGx variety as host resulted primarily from higher Nitrogenaseactivity per unit nodule mass (specific acetylene reduction activity) andhigher nodule number per plant. The higher N2-fixation capabilities of Bradyrhizobium japonicum with unimproved Gazelle variety as host resultedprimarily from higher nodule mass per plant which was associated with wasassociated with higher nodule numbers.