Abstract

Bio-synthesised silver nanoparticles are effective in controlling several micro-organisms. They are correspondingly environmentally friendly, affordable, and easy to synthesise when compared with chemically synthesised silver nanoparticles. This study investigated the efficacy of biosynthesized silver nanoparticles against the fungus Sporisorium scitamineum, the causal agent of sugarcane smut. The reduction of silver nitrate upon mixing with the plants’ crude extracts was evidenced by the change in colour of the mixture to dark brown. Optimization of the mixtures using ultraviolet-visual spectroscopy showed peaks in the range of 340 to 450 nm. The Fourier transform infrared spectroscopy analysis identified proteins to be essential capping agents, and reducing sugars were responsible for the reduction of silver nitrate to nanoparticles and stabilizing the nanoparticles. The transmission electron microscope analysis showed the sizes of the nanoparticles to vary between 3 and 70 nm. Carissa spinarum and Melia azedarach had the most antifungal activity against S. scitamineum as observed from the inhibition-zone assay. Silver nanoparticles were successfully synthesized using the selected botanicals. All the synthesized nanoparticles showed varying antifungal effects against the S. scitamineum. C. spinarum and M. azedarach exhibited the highest antifungal activity, while Azadirachta indica showed the least.

Key words: Sporisorium scitamineum, Acacia nilotica, Carissa spinarum, Senna didymobotrya, Warburgia ugandensis, Melia azedarach, Azadirachta indica, bio-synthesised silver nanoparticles, antifungal activity.