Growth and biochemical responses of soybean to double and triple microbial associations with Bradyrhizobium, Azospirillum and arbuscular mycorrhizae

► Root biomass enhanced by microbial associations. ► B + A gave the highest biomass. ► B + M had a transitory negative effect on nodulation. ► B + A + M reduced shoot biomass and increased proline content. ► Coumestrol, a putative common regulating signal for A and M.