Streptomyces eurocidicus promotes soybean growth and protects it from fungal infections

The aim of this work was to analyze Streptomyces eurocidicus as growth promoter for soybean (Glycine max (L.) Merr.) plants and to study the role of antifungal polyene eurocidin produced by this strain on the biocontrol over two soybean phytopathogenic fungi, Macrophomina phaseolina and Diaporthe aspalathi, which are generally controlled by environmentally harmful chemical antifungals and genetic resistance, respectively. In vitro studies confirmed that the eurocidin producer S. eurocidicus inhibited these pathogens as well as several other important phytopathogenic fungi, while non-antagonistic effect on Bradyrhizobium japonicum was observed. Phenotypic characterization of S. eurocidicus strain showed its potential as growth promoter agent, a property probably related with its ability to produce siderophores and 3-indolacetic acid and also to solubilize tricalcium phos-phate. Moreover, the results obtained demonstrate that seeds treatment with S. eurocidicus promotes soybean plants growth and development, either alone or in combination with B. japonicum in vegetative stage and also, enhances seeds produced per plant at crop maturity under greenhouse conditions. Biocontrol experiments using soybean-M. phaseolina and soybean-D. aspalathi pathosystems showed that the polyene-producer S. eurocidicus and a eurocidin non-producer mutant strain protect soybean plants reducing the severity of both diseases. These results suggested that there is/are another mechanism/s for soybean plants protection independent of the polyene antifungal per se. Altogether these results demonstrate that S. eurocidicus is a good biocontrol agent and also a growth and development promoter; and strongly support further research on this field in order to pursue their use to sustainably manage crop diseases while stimulating plant growth.