The Interaction between Bradyrhizobium Japonicum E109 and Azospirillum Brasilense Az39 Improves Bradyrhizobium-Soybean Symbiosis: The Secrets Behind Co-Inoculation

Aims The aim of this work was evaluating the interaction between two of the most widely used strains for soybean inoculation in Argentina, B. japonicum E109 (BjE109) and A. brasilense Az39 (AbAz39). Methods Five treatments were performed: (i) uninoculated seeds; (ii) seeds inoculated with BjE109; (iii) seeds inoculated with AbAz39; (iv) seeds co-inoculated with BjE109 and AbAz39 in a 1:1 proportion (BjE109 + AbAz39) at the seeds sowing and (v) seeds inoculated with a 1:1 proportion of BjE109 and AbAz39 (BjE109-AbAz39) 24 h before seeds sowing. Each treatment was assessed through a seed recovery assay, glasshouse assays and field assays. Results The combination between the two strains improved the ability of BjE109 to survive on soybean seeds after inoculation partially explained by AbAz39’s capacity to produce diverse biologically active molecules. As a result of the greater rhizobial survival on seeds the nodulation values and symbiosis parameters like nodule number, size and biomass and nodulation percentage also increased. In agreement with these observations, combining BjE109 and AbAz39 at strains the grain yield under field conditions were 13,3 and 17,3% greater than single BjE109 inoculation. Conclusions These results here show that the pre-culture combining BjE109 and AbAz39 before the inoculation to the soybean seeds has benefits in plant nodulation and hence production, more than individual inoculation with BjE109 or AbAz39, or the immediate co-inoculation of both strains.