Antifungal Metabolites of Streptomyces chrestomyceticus STR-2 Inhibits Magnaporthe oryzae, the Incitant of Rice Blast.

Rice, a staple food crop worldwide, suffers devastating yield losses as a result of blast disease caused by Magnaporthe oryzae Cav. The adverse effects of chemicals on the environment are rising concerns for sustainable and eco-friendly approaches. The use of antagonistic microbes for the management of rice blast appears to be a sustainable solution to this challenge. Herein, we isolated 20 Streptomyces strains from rice rhizosphere, among which the isolate STR-2 exhibited maximum inhibition of mycelial growth of M. oryzae accounting for 50% reduction over control. The isolate STR-2 was identified as S. chrestomyceticus through 16S rRNA gene sequencing. In vitro tests demonstrated its ability to produce antifungal and bioactive compounds and also synthesize siderophore, IAA, and phosphate-solubilizing agents, thereby promoting plant growth upon inoculation on rice seeds. GC-MS analysis showed the presence of volatiles, antifungal, antimicrobial, and antioxidant compounds with different retention times. The crude antibiotic extract of 0.5% of S. chrestomyceticus STR-2 reduced the mycelial growth of M. oryzae over the control. Application of talc-based formulation of Streptomyces chrestomyceticus STR-2 resulted in the least disease incidence (15.89%) with the highest disease reduction of 65.26% over untreated control under field condition. These findings indicate the potential of S. chrestomyceticus as a potential bio-inoculant against rice blast disease.