The expansion of the soybean crop has evidenced a high host specificity, indicating the requirement of new strains with capacity of nodulating soybean and competition capacity with the natural soil rhizobial population. The purpose of this study was to evaluate the host specificity of mutants isolated from Bradyrhizobium spp strains in relation to nodulation and relative N2 fixation effectiveness in soybean (cultivars Peking and Clark), cowpea and pigeon pea. The experiment was carried out under controlled conditions in a growth chamber, where B. japonicum and B. elkanii mutants and the respective original strains were tested for their nodulation ability on soybean, cowpea and pigeon pea. The crop was harvested 35 days after planting and the nodulation (number, dry nodule weight), shoot dry matter production and relative N2 fixation effectiveness were evaluated. The mutants and strains of Bradyrhizobium spp nodulate Glycine max (cultivars BR-16, Clark and Peking), Vigna unguiculata and Cajanus cajan, however the interaction rhizobia-leguminous demonstrated significant symbiotic effectiveness for Glycine max only.
host specificity; Bradyrhizobium japonicum; Bradyrhizobium elkanii
