GENOTYPE X BRADYRHIZOBIUM-JAPONICUM STRAIN INTERACTIONS IN DINITROGENFIXATION AND AGRONOMIC TRAITS OF SOYBEAN (GLYCINE-MAX L MERR)

Bradyrhizobium japonicum strain G49 has been the only inoculum used in French soils. Soybean (Glycine max L. Merr.) cultivars were selected and tested according to their performances with this rhizobial strain. The aim of the present study was to determine the consequences of str ain substitution on N-2 fixation abilities of various genotypes. Three genotypes and cultivar Weber, in combination with B. japonicum strain G49 or SMGS1, were cultivated in pots and tested for nitrogenase acti vity under differing nitrogen nutrition conditions. The reliability of ARA (acetylene reduction activity) measurement for assessing symbioti c nitrogen fixation under the experimental conditions used was checked . Genotypic variability for symbiotic fixation activity was observed w ith each strain under soil culture conditions; important genotype x st rain interactions were also involved. These results were corroborated for the protein yield and other yield component performances of the va rious genotype-strain associations. Thus, in France, the replacement o f strain G49 with another one might result in the alteration of the re lative agronomic performances of the soybean cultivars, since N-2 fixa tion is considered as a major factor of soybean productivity.