Antifungal Activity of Methanolic Leaf Extract of Gmelina arborea Roxb. ex Sm. AGAINST Fusarium oxysporum Schltdl Causing Damping -Off Disease

Abstract

Fusarium oxysporum, the causal agent of damping-off disease, is a destructive soilborne pathogen that significantly reduces seedling establishment and crop yield. Although synthetic fungicides remain effective in controlling this pathogen, their continuous and excessive use has led to challenges such as resistance development, environmental pollution, and health hazards. In this study, the antifungal activity of methanolic leaf extract of Gmelina arborea Roxb. ex Sm. was evaluated against F. oxysporum causing damping off disease. Fresh leaves of Gmelina arborea were collected, authenticated, dried, and extracted using 70% methanol by maceration. Pure strains of Fusarium oxysporum were obtained and identified from Mycology Laboratory, Department of Crop protection, Ahmadu Bello University, Zaria. Phytochemical screening of Gmelina arborea leaf extract revealed the presence of alkaloids, flavonoids, phenols, tannins, saponins, terpenoids, steroids, and cardiac glycosides, while anthraquinones were absent. Quantitative analysis showed high levels of flavonoids (125.41 mg/g) and phenols (124.98 mg/g), both known for their antimicrobial activity. The antifungal effect of the extract was tested in vitro by incorporating graded concentrations (5–25 mg/mL) into potato dextrose agar and monitoring mycelial growth inhibition. Results demonstrated a concentration-dependent effect, with maximum inhibition (68.3%) observed at 20 mg/mL. Interestingly, inhibition decreased at 25 mg/mL (54.9%), possibly due to antagonistic interactions at higher concentrations. These findings demonstrate that G. arborea possesses promising antifungal potential against F. oxysporum. The presence of bioactive phytochemicals, particularly flavonoids and phenols, likely accounts for the observed inhibitory effects. Therefore, the extract could serve as a natural alternative to synthetic fungicides in the management of damping-off disease.