Endophytic Streptomyces sp. N2A protects soybean against fungal diseases through two distinct mechanisms

Abstract

Endophytic Streptomyces sp. N2A and S. lydicus N9 isolated from soybean were previously demonstrated as biostimulants of soybean (Glycine max (L.) Merr.) crop increasing yield and seed phytosanitary quality at field conditions. Here both strains were tested and effectively biocontrol Charcoal Rot (CR) caused by Macrophomina phaseolina and Soybean Stem Canker (SSC) caused by Diaporthe aspalathi. Induced systemic resistance was demonstrated by the increased expression of both SA and JA/ET signaling pathways associated genes pre- and post-fungal pathogen inoculation in plants treated with each actinobacterium, in both pathosystems. Also, H2O2 accumulation was observed in S. sp. N2A-treated plants after pathogen challenge. Moreover, the priming effect was also demonstrated on growth parameters for bacterial-treated plants after infection with D. aspalathi. Both strains produce ribosomal lipopeptide antibiotic of broad-spectrum effect over fungus and Gram-positive bacteria; known as albopeptide produced by S. sp. N2A and solabiomycin produced by S. lydicus N9. Biocontrol assays of CR showed decreased protection in soybean plants pre-treated with an albopeptin non-producer N2A mutant strain, demonstrating that S. sp. N2A could efficiently control fungal diseases, at least, via two distinct and complementary mechanisms of antibiosis and ISR in soybean. These results, strongly supports further development to formulate a biostimulant and biofungicide agent based on this soil bacteria to increase yield and control fungal diseases of great impact on the crop sustainably.