Biocontrol efficacy of Streptomyces species and their silver nanoparticles derived from secondary metabolites against early blight disease of tomato

Muhammad Kamal Rashid & Tavga Sulaiman Rashid

Sydowia 79: 223-233

Published online on October 6th, 2026

Streptomyces species are known for their ability to produce bioactive compounds of potential agricultural value. Two Streptomyces isolates (M1 and M5) were investigated for secondary metabolites as well as for their ability to assist in the biosynthesis of silver nanoparticles (AgNPs). AgNPs were synthesized using the metabolite extracts, and AgNPs formation was confirmed by UV–Vis spectrophotometry, Fourier Transform Infrared Spectroscopy (FTIR), and Energy Dispersive Spectroscopy (EDS). The bioassay test confirmed that Streptomyces gilvosporeus isolate M1 secondary metabolites were active against Alternaria solani with an inhibition rate of 64.8 %. It is interesting to note that AgNPs synthesized from the same strain were more inhibitory (86.8 %). Metabolites of Streptomyces sp. isolate M5 were non-inhibitory to A. solani, but its AgNPs were moderately inhibitory at 46.6 %, hence confirming that the process of nanoparticle formation significantly enhanced the antifungal activity of this strain. Morphological analysis showed that AgNPs biosynthesized using both isolates were spherical with a diameter of 14.57 nm for M1, whereas isolate M5 were bigger in diameter (68.69 nm). Besides antifungal action, the AgNPs biosynthesized also promoted growth of the plant through enhanced root length, chlorophyll content, and biomass when compared with secondary metabolite treatment or fungicide. Overall, Streptomyces-derived secondary metabolites as well as AgNPs showed antifungal activity, where AgNPs showed comparatively enhanced bioactivity and growth promotion in plants. The findings signify the dual use of Streptomyces-mediated AgNPs as antifungal and plant growth promoters. Further research on Streptomyces metabolites and uses of their nanoparticle-mediated potential can likely result in the discovery of novel bioactive compounds and environmentally friendly approach for the control of plant diseases.

Keywords: green nanoparticle, biological control, Alternaria solani, actinomycetes, PGPR

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