Efficacy of Neem (Azadirachta indica) Leaf Extract Against Fungi Pathogen Associated with Watermelon (Citrullus lanatus) Spoilage

Background and Objective: Watermelon (Citrullus lanatus) is a member of the Cucurbitaceae family native to Africa and has been cultivated since ancient times. Reports of chemo-resistance pathogens and health implications have stalled the application of agrochemicals for improving fruit production. This led to the isolation, purification, identification of pathogens and use of Azadirachta indica leaf extract to inhibit pathogenic growth responsible for post-harvest deterioration of watermelon (Citrullus lanatus). The study aims to isolate, purify and determine growth rate, zone of inhibition and colony count of fungi pathogen of watermelon using standard mycological techniques to ascertain the effectiveness of Azadirachta indica leaf extract on the pathogen. Materials and Methods: Sample collection and media preparation, culture and purification of isolates, pathogenicity test, as well as neem leaf aqueous extract, were conducted using standard pathological methods in this research, after which five fungi pathogens such as Aspergillus flavus, Fusarium oxysporum, Aspergillus niger, Rhizopus sp. and Saccharomyces sp. They were isolated from infested watermelon fruits and treated with 5, 10, 20 and 40 g concentrations of neem extracts where 5.4, 5.8, 6.1 and 6.6 cm inhibition rates were observed. Results: Aspergillus species appeared undeterred by the extract at these concentrations, but the overall inhibitory potential of neem leaf extracted was observed at 40 g inhibitory concentration at 50% concentration (IC₅₀). This means that the higher the concentration of the neem extract, the more effective in inhibiting pathogenic diseases of watermelon. Findings revealed that at controlled doses, Azadirachta indica leaf extracts may be able to suppress post-harvest pathogenic fungus in watermelon. Conclusion: To get compounds with significant resistance to post-harvest rotting, bioactive components should be assessed via bioassay-guided isolation.