In-vitro Antifungal Efficacy of Neem leaf (Azadirachta indica) and Garlic (Allium sativum) Extracts against Phytopathogenic Fungi of Watermelon in Dutse, Jigawa State, Nigeria

Abstract

Watermelon (Citrullus lanatus) is a widely cultivated fruit crop in Dutse, Jigawa State, Nigeria, valued for its nutritional and economic importance. However, its production faces increasing challenges from fungal infections that cause significant pre and post-harvest losses. The objective of this study was to isolate and identify fungal pathogens associated with infected watermelon fruits and to evaluate the antifungal effects of neem (Azadirachta indica) and garlic (Allium sativum) extracts. Infected fruit samples were collected from three major markets in Dutse and analyzed using standard isolation and morphological techniques. Aspergillus niger was the sole fungal pathogen identified. Methanolic extracts of neem leaves and garlic bulbs were prepared and screened for phytochemicals, revealing the presence of alkaloids, saponins, terpenoids, and flavonoids. Antifungal activity was assessed at concentrations of 5, 10, and 15 mg/mL using the agar well diffusion method. Both extracts exhibited significant, concentration-dependent antifungal activity against A. niger (p < 0.05), with inhibition zones of 55.50 mm (neem) and 52.80 mm (garlic) at 15 mg/mL. Minimum inhibitory concentration (MIC) tests showed that garlic inhibited fungal growth at 5 mg/mL, while neem required at least 10 mg/mL. The results confirm that both extracts possess strong antifungal properties, with neem being more effective at higher concentrations and garlic at lower ones. Neem and garlic extracts present promising potential as affordable, eco-friendly alternatives to synthetic fungicides for managing watermelon fungal pathogens. Further research is suggested on formulation development, field application, and mechanisms of action to support their use in sustainable agriculture. Voucher specimens of Azadirachta indica (FUD-BOT/MI/013/2025), Allium sativum (FUD-BOT/MI/014/2025) and Citrullus lanatus FUD-BOT/MI/015/2025) were authenticated and deposited at the Department of Plant Biology, Federal University Dutse.