Phyto-Synthesis and Characterization of Silver Nanoparticles Using Box-Behnken Design and Its Anti-Alternaria Activity

Alternaria alternata is a global fungal pathogen that causes symptoms such as leaf blight and seed rot resulting in economically significant yield losses in different varieties of crops. Green synthesis of nanoparticles is preferred over other methods of synthesis due to their safety, eco-friendly approach, and cost-effectiveness. Phyto-synthesis of silver nanoparticles (Ag-NPs) using seed extract of Abrus precatorious was optimized and characterized using the Box-Behnken design (BBD). Ag-NPs with a UVmax of 409.01 nm and a crystallite and particle size of 23.75 and 34.36 nm, respectively, were synthesized. In vitro anti-alternaria activity of Ag-NPs showed a concentration-dependent inhibition of the mycelia with a maximum inhibition of 54.61% at 200 ppm which was significantly different ( p < 0.05) from propiconazole (1 ppm) with 100% inhibition. A scanning electron micrograph (SEM) of mycelia treated with 200 ppm of Ag-NPs showed a shrunken and shriveled mycelia while the ultrastructure of the mycelia under a transmission electron microscope (TEM) showed the alteration of the fungus cell wall and disappearance of cellular organelles compared to the control sample, while energy dispersive x-ray spectroscopy (EDX) analysis of the mycelia showed the localization of elemental Ag (0.95%) within the cell of the fungus compared to the control. The results of this study highlighted the antifungal potential of Ag-NPs against fungicide-resistant Alternaria alternata to reduce the environmental impact of synthetic fungicides.