Influence of antibiosis produced by actinomycetes on strains of Bradyrhizobium spp. on soybean nodulation

The aim of this work was to evaluate the antibiotic spectrum of actinomycet es from Cerrado soils and their influence on soybean nodulation. Strains BR 29, BR 33, BR 40, BR 85, BR 86, BR 96, 47/587, 3B-7 and 4A-5 of Bradyrhizo bium spp. were characterized by their natural resistence to antibiotics pro duced by 204 actinomycete isolates. The strains BR 29 and BR 96 of B, elkan ii were sensitive to 5.2% and 9.9% the products of actinomycete isolates, r espectively, while BR 33 was sensitive up to 20.3%. The antagonistic effect s caused by actinomycete exclusively to BR 29 and BR 33 were 1.6% and 5.7% respectively. This effect was not observed for strains BR 40 and BR 96. Sin gle and multistrains inoculations in the presence or absence of actinomycet es affected soybean nodulation. On double strain inoculations, with BR 33 a nd BR 29 mixed with actinomycete 370 there was a decrease in nodule occupan cy by BR 29 from 94.1% to 83.7% with concomitant increase in the occupying of BR 33 from 6.7% to 17.2%. The results indicate the importance of ecologi cal studies on actinomycetes population in order to access their role in th e establishment of efficient nodulation.