Comparative Studies of the Antifungal Properties of Mango and Orange Leaves in the Prevention of Gummy Stem Blight in both Water Melon and Cucumber

Abstract

Gummy stem blight, caused by the fungal pathogen Didymella bryoniae, is a significant disease of watermelon (Citrullus lanatus) and cucumber (Cucumis sativus), leading to reduced yield and economic losses.  Fungicides are commonly used to manage this disease; however, they pose risks such as environmental pollution, fungal-resistance and food safety concerns.  There is need to explor plant-based alternatives due to their biodegradability, safety and eco-friendliness. This study evaluated phytochemical composition and in vitro antimicrobial potential of ethanolic and methanolic leaf extracts of orange (Citrus sinensis) and mango (Mangifera indica) against Didymella bryoniae, the causal agent of gummy stem blight in watermelon and cucumber. Leaf extracts were prepared using Soxhlet extraction with methanol and water as solvents, and the agar well diffusion method was employed for the susceptibility assay. Preliminary fungal identification was based on conidial and colony morphology, Pathogenicity was conducted on fresh test plants to ensure the organism caused the disease. Phytochemical analysis revealed the presence of tannins, flavonoids, carbohydrates, steroids, and alkaloids in both extracts, with orange leaf extract exhibiting a high concentration of alkaloids and cardiac glycosides (+++). Saponins and anthraquinones were absent in both extracts. Methanolic orange leaf extract demonstrated the highest antifungal activity, with zones of inhibition measuring 88.00 mm and 80.00 mm at concentrations of 200 mg/mL and 150 mg/mL, respectively. In contrast, methanolic mango leaf extract exhibited inhibition zones of 62.23 mm and 57.89 mm at the same concentrations. The lowest concentration (12.50 mg/mL) showed minimal activity (20.21 mm). Fluconazole, used as a control, exhibited inhibition zones of 100 mm at similar concentrations. Statistical analysis indicated significant differences (P < 0.05) in the inhibition zones among the various concentrations and between the extracts and the control. The results suggest that orange leaf extract is more effective than mango leaf extract in inhibiting Didymella bryoniae.