Suppression of Phytopathogenic Fungi by Plant Extract of Some Weeds and the Possible Mode of Action

Aims: The goal of this work was to emulate the antifungal properties of some newly collected weeds against important phytopathogenic fungi: Pythium ultimum, Penicillium expansum and Fusarium solani. The mode of action through which the extracts could affect the target fungi was studied.

Place and Duration of Study: Department of Biology, Faculty of Science, King Khalid University, Saudi Arabia, between February, 2014 and May, 2015.

Methodology: Ten plant species were obtained from Aseer region. The plant extract obtained by ground dry plant material to be a fine powder and shaking in chloroform, ethanol or hexane. Screening of antifungal activity of the plant extracts was carried out against the phytopathogenic fungi grown on Czapek’s agar medium using disc diffusion method and the minimum inhibitory concentration was determined. The treated fungal samples were examined and photographed using the scanning electron microscope to define the alteration and malformation in the fungal hyphae. The chemical composition of the most active plant extracts was determined using gas chromatography–mass spectrometry (GC–MS).

Results: Preliminarily test of the crude extract of the weed plants showed antifungal activity against all organisms but in various extent. The crude extract of Foeniculum vulgare showed the highest antifungal activity against the three phytopathogens. Scan electron microscopy (SEM) approved a clear morphological malformation in the hyphae and spores supported the assumption that the mechanism involved in killing the fungus includes the altering of cell membrane permeability that leads to the plasmolysis of the cells and changing their shape. Gas chromatography–mass spectrometry (GC-MS) analysis results showed that many aliphatic and aromatic compounds were identified in the different extracts. The main observation was the number and types of the detected compounds have greatly depended on the type of the extract. We assume that many compounds in each extract act in synergetic effect to destruct the fungal cell integrity and involved in their death.

Conclusion: The plant extract of Foeniculum vulgare is a promising natural product that could be applied in control of many phytopathogenic fungi as an alternative to hazard chemical fungicides.