Abstract
Senna alexandrina Mill leaves are widely used in traditional medicine for its pharmacological properties. The present study was designed to evaluate antifungal activities of solvent extracts from S. alexandrina leaves against human and phytopathogenic fungi, including plant pathogens, Alternaria alternata, Fusarium monoliforme, F. oxypsporum, F. solani and Helminthosporium sativum, and human pathogens, Candidia albicans, C. famata, C. krusei, and C. parapsilosis. Poisoned food and agar well diffusion methods were used to assess antifungal activity. Acetone, methanol and aqueous extracts were prepared and screened; methanol and aqueous extracts were effective in inhibiting the growth of some phytopathogens. However, Candida spp were resistant towards all solvent extracts. Maximum growth inhibition was observed with methanol and aqueous extracts for Fusarium monoliforme (85%) and F. solani (76%) at a concentration of 0.5 mg/mL. Minimum inhibitory concentration (MIC) and minimum fungicidal concentrations (MFC) ranged between 1-128 mg/mL. Scanning and transmission electron microscopy (SEM and TEM) of fungal isolates at MIC concentrations revealed severe damage to cell morphology and ultrastructure. Distorted and shriveled hyphae as well as peeled and damaged conidia were evident in SEM microphotographs. Similarly, TEM microphotographs showed underdeveloped cells, shrunken cytoplasm, membrane bulging and membranes absence. Fourier-transform infrared spectroscopic analysis of methanol and aqueous extracts showed the presence of important functional groups, including phenols, alcohols, aromatic compounds, and flavonoids. Senna alexandrina leaf extracts can serve as a useful alternative to harmful fungicides for control of plant pathogens.