Characterization of endophytic Streptomyces griseobrunneus Ahn75 and its potential for biocontrol and plant growth-promotion in rice

Abstract Plant endophyte Streptomyces are excellent candidates as biocontrol agents against the rice blast fungus, Magnaporthe oryzae. In this study, rice endophytic strain Ahn75 was isolated from healthy rice stem and identified as Streptomyces griseobrunneus by morphological and molecular characterization. Then the potential of strain Ahn75 for inhibition against M. oryzae and growth-promotion were evaluated using an in vitro assay, genome sequencing, and in vivo greenhouse pot experiments. Strain Ahn75 significantly inhibited the growth of M. oryzae, and its culture filtrate caused 80.88% mycelia growth inhibition, 78.26% spore germination inhibition and significant morphological alterations in M. oryzae. Meanwhile, strain Ahn75 also exhibited several growth-promoting properties, including phosphate and potassium solubilization, siderophore production, and nitrogen fixation. Genome sequencing results showed 40 gene clusters of secondary metabolites, including lactones, non-ribosomal peptide synthetases (NRPS), siderophores, polyketide antibiotics, terpenes, and peptides, that may synthesize active compounds against M. oryzae, and several genes related to plant growth promotion were exhibited in the genome of Ahn75. In greenhouse test, Ahn75 dramatically reduced rice leaf blast incidence by 59.76% and increased grain yield by 55.57% and 59.22% in wet and dry weight, respectively. These findings suggest that strain Ahn75 could be a potential biocontrol and growth-promoting agent for rice.