Phytotoxic Effects of Neem Oil Nanoemulsion on Maize (Zea mays L.) Seed Germination and Seedling Vigour

Aim: This study aimed to develop a stable, eco-friendly antifungal seed treatment using neem oil nanoemulsion (NON) enhanced with green-synthesised silver nanoparticles (AgNPs) derived from Terminalia cattapa leaf extract. The NON was characterised by a mean particle size of 44.58 nm and a polydispersity index (PDI) of 0.945, indicating high stability. Study Design: Experimental Laboratory Study Place and Duration of Study: Department of Crop Protection, Faculty of Agriculture, University of Abuja, and Centre for Genetic Engineering and Biotechnology, Federal University of Technology, Minna. Nigeria, between September and November 2024. Methodology: Neem oil nanoemulsion (NON) achieved 100% fungal growth inhibition at all tested concentrations (600–1000 mg/mL), with identical inhibition zones (34.00 ± 0.50 mm; p > 0.05), suggesting a saturation effect at the lowest tested dose. Low concentrations (6.25–25 mg/mL) significantly enhanced germination (94.4–100%; p < 0.05) and vigour index (0.52–0.60), while higher concentrations (50–100 mg/mL) suppressed germination (≤77.8%) and induced phytotoxicity. Antioxidant assays showed superior radical scavenging activity (DPPH: 80.12%; FRAP: 86.59%) compared to raw neem oil. Result: Agar well diffusion assays demonstrated complete fungal growth inhibition (100%) across concentrations of 600–1000 mg/mL, with consistent inhibition zones (34.00 ± 0.50 mm). Phytotoxicity assessments revealed that low NON doses (Ne6.25–Ne25 mg/mL) enhanced germination (94.4–100%) and seedling vigour, while higher doses (Ne50–Ne100 mg/mL) suppressed growth and reduced germination (≤77.8%). Antioxidant assays demonstrated superior radical scavenging activity (DPPH: 80.12%; FRAP: 86.59%) compared to raw neem oil. Conclusion: NON is a promising sustainable alternative to synthetic fungicides, with dual benefits of pathogen suppression and growth stimulation at low doses. However, precise dose calibration is essential to avoid phytotoxic effects. Field validation, long-term stability testing, and environmental safety assessments are recommended.