Biogenic Synthesis of Silver Nanoparticles from Horticultural Plant Extracts and their Efficacy Against Post-Harvest Fungal Pathogens of Vegetables in Nigeria

Post-harvest fungal contamination of vegetables represents a major food safety and economic loss challenge in Nigeria, and conventional synthetic fungicide treatments face growing regulatory restrictions and resistance development. Biogenic silver nanoparticles synthesized from plant extracts offer an innovative, low-toxicity alternative with demonstrated broad-spectrum antifungal activity. This dissertation develops and characterizes silver nanoparticles biogenically synthesized from extracts of three Nigerian horticultural plants, neem (Azadirachta indica), bitter leaf (Vernonia amygdalina), and pawpaw leaf (Carica papaya), and evaluates their in vitro and in vivo antifungal efficacy against dominant post-harvest pathogens of tomato, pepper, and cucurbits in Nigeria. Synthesis optimization using response surface methodology identified extraction solvent concentration, silver nitrate molarity, and incubation time as critical parameters. Nanoparticle characterization was performed using UV-Vis spectroscopy, TEM, XRD, and FTIR. Antifungal efficacy was assessed against Fusarium oxysporum, Alternaria alternata, and Rhizopus stolonifer using disc diffusion assays and post-harvest disease suppression trials. Results indicate that neem-synthesized silver nanoparticles exhibited the strongest antifungal activity, with minimum inhibitory concentrations 4 to 8 times lower than commercial thiram fungicide, and no detectable phytotoxicity at effective concentrations in fruit coating trials. The study establishes a scalable biogenic nanoparticle synthesis protocol with significant potential for development as a post-harvest antifungal technology for the Nigerian horticultural sector. Keywords: silver nanoparticles, biogenic synthesis, antifungal, post-harvest pathogens, Nigeria