Antifungal Activity and Fourier Transform Infrared Spectrometric Characterization of Aqueous Extracts of Acacia senegal and Acacia tortilis on Phytopathogenic Fungi

Abstract

Objective: To evaluate the in vitro antifungal activity of aqueous extracts of Acacia senegal (A. senegal) and Acacia tortilis (A. tortilis) against three phytopathogenic fungi (viz., Alternaria alternata [A. alternata], Helminthosporium rostratum [H. rostratum] and Fusarium solani [F. solani]). Methods: Crude aqueous extracts of A. senegal and A. tortilis at 1%, 2.5% and 5% concentrations were used for screening. Antifungal activities of the extracts were evaluated against three phytopathogenic fungal strains (A. alternata, H. rostratum and F. solani) by poisoned food technique. Scanning electron microscopy (SEM) of the treated and untreated mycelia was employed to analyze the ultrastructural changes and Fourier-transform infrared (FTIR) spectrometry analysis was performed to identify important functional groups. Results: Aqueous extract of A. tortilis at high concentrations exhibited moderate inhibitory activity against the selected fungal strains. The aqueous extract of A. senegal showed no effect on A. alternata, while exhibited very mild activity against H. rostratum and F. solani at high concentrations (2.5% and 5%). Scanning electron microphotographs of the untreated fungal cells showed no structural changes (well‒defined mycelium and conidia without any distortion), whereas the treated cells showed structural distortions, twisted and wrecked mycelia and showed the presence of vesicles on the surface. FTIR analysis showed the presence of important functional groups such as alcohols, carboxylic acids and aromatic compounds. Conclusion: Results from this study indicate that the aqueous extracts of both A. senegal and A. tortilis have the potential to be used as natural fungicidal agents in the management of diseases caused by plant pathogenic fungi.