Streptomyces N2A, an endophytic actinobacteria that promotes soybean growth and increases yield and seed quality under field conditions

Sustainable agriculture based on the use of soil-beneficial microbes such as plant growth-promoting rhizobacteria (PGPR) and biocontrol agents (BCA) is gaining great consideration to reduce the use of agrochemicals for crop production. With this aim, in this study, a total of 78 actinobacteria were isolated from the rhizosphere and endosphere of soybean roots. Based on in vitro compatibility with Bradyrhizobium japonicum, the ability to produce phytohormones, siderophores, exo-enzymes, antifungal compounds and phosphate solubilization (PGPR traits), two endophytic strains, named N2A and N9, were selected to evaluate their effects on plant growth and development at greenhouse and field conditions. Greenhouse trials showed significantly promoted seedling emergence compared to control and the conventional fungicide treatment. Analysis of growth and development associated parameters at reproductive stages and maturity at greenhouse, but also and most importantly, in field experiments showed significant improvements. Plant biomass, node number, pod number, and consequently yield, were higher in plants previously treated with N2A and co-inoculated with B. japonicum compared to the conventional seed treatment. Furthermore, a significant increase in health status and vigor was observed for seeds harvested from the N2A-treated plants in relation to seeds obtained from the conventional treatment. Thus, we demonstrated that Streptomyces sp. N2A can replace traditional chemical fungicides to protect the seed during germination, allowing good implantation, but also, stimulating the growth and development of soybean crop increasing yield and seed quality at field conditions. Altogether, this supports the potential use of Streptomyces N2A as a PGPR for soybean crop production more efficiently and sustainably.