Antifungal Activity of Isolated Compounds from the Leaves of Combretum erythrophyllum (Burch.) Sond. and Withania somnifera (L.) Dunal against Fusarium Pathogens

Hlabana Alfred Seepe; Tselane Geneva Ramakadi; Charity Mekgwa Lebepe; Stephen O Amoo; Winston Nxumalo

doi:10.3390/molecules26164732

Antifungal Activity of Isolated Compounds from the Leaves of Combretum erythrophyllum (Burch.) Sond. and Withania somnifera (L.) Dunal against Fusarium Pathogens

Molecules. 2021 Aug 5;26(16):4732. doi: 10.3390/molecules26164732.

Authors

Hlabana Alfred Seepe^{1

2}, Tselane Geneva Ramakadi², Charity Mekgwa Lebepe², Stephen O Amoo^{1

3

4}, Winston Nxumalo²

Affiliations

¹ Agricultural Research Council-Vegetables, Industrial and Medicinal Plants, Roodeplaat, Private Bag X293, Pretoria 0001, South Africa.
² Department of Chemistry, University of Limpopo, Private Bag X1106, Sovenga 0727, South Africa.
³ Indigenous Knowledge Systems Centre, Faculty of Natural and Agricultural Sciences, North-West University, Private Bag X2046, Mmabatho 2735, South Africa.
⁴ Department of Botany and Plant Biotechnology, Faculty of Science, University of Johannesburg, P.O. Box 524, Auckland Park 2006, South Africa.

Abstract

Crop diseases caused by Fusarium pathogens, among other microorganisms, threaten crop production in both commercial and smallholder farming. There are increasing concerns about the use of conventional synthetic fungicides due to fungal resistance and the associated negative effects of these chemicals on human health, livestock and the environment. This leads to the search for alternative fungicides from nature, especially from plants. The objectives of this study were to characterize isolated compounds from Combretum erythrophyllum (Burch.) Sond. and Withania somnifera (L.) Dunal leaf extracts, evaluate their antifungal activity against Fusarium pathogens, their phytotoxicity on maize seed germination and their cytotoxicity effect on Raw 264.7 macrophage cells. The investigation led to the isolation of antifungal compounds characterized as 5-hydroxy-7,4'-dimethoxyflavone, maslinic acid (21-hydroxy-3-oxo-olean-12-en-28-oic acid) and withaferin A (4β,27-dihydroxy-1-oxo-5β,6β-epoxywitha-2-24-dienolide). The structural elucidation of the isolated compounds was established using nuclear magnetic resonance (NMR) spectroscopy, mass spectroscopy (MS) and, in comparison, with the available published data. These compounds showed good antifungal activity with minimum inhibitory concentrations (MIC) less than 1.0 mg/mL against one or more of the tested Fusarium pathogens (F. oxysporum, F. verticilloides, F. subglutinans, F. proliferatum, F. solani, F. graminearum, F. chlamydosporum and F. semitectum). The findings from this study indicate that medicinal plants are a good source of natural antifungals. Furthermore, the isolated antifungal compounds did not show any phytotoxic effects on maize seed germination. The toxicity of the compounds A (5-hydroxy-7,4'-dimethoxyflavone) and AI (4β,27-dihydroxy-1-oxo-5β,6β-epoxywitha-2-24-dienolide) was dose-dependent, while compound B (21-hydroxy-3-oxo-olean-12-en-28-oic acid) showed no toxicity effect against Raw 264.7 macrophage cells.

Keywords: apigenin; maslinic acid; natural products; phytotoxicity; purification; salvigenin; withaferin A.

MeSH terms

Animals
Antifungal Agents / pharmacology*
Combretum / chemistry*
Fusarium / drug effects*
Mice
Microbial Sensitivity Tests
Plant Extracts / pharmacology*
Plant Leaves / chemistry*
RAW 264.7 Cells
Withania / chemistry*

Substances

Antifungal Agents
Plant Extracts

Grants and funding

NRF Grant No 98670/National Research Foundation