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

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.

Antifungal Potential of Canarian Plant Extracts against High-Risk Phytopathogens

“…This fact could be attributed to the potential antifungal activity of some withanolide derivatives that are soluble in water. Thus, Seepe et al [ 66 ] reported that a withaferin A glycoside isolated from a Whitania species was active against Fusarium verticilloides.…”

Biocontrol of Fusarium graminearum, a Causal Agent of Fusarium Head Blight of Wheat, and Deoxynivalenol Accumulation: From In Vitro to In Planta

“…Moreover, selenium nanoparticles (SeNPs) synthesized by Lactobacillus acidophilus ML14 controlled F. culmorum and F. graminearum growth based on their powerful antioxidant and antifungal activities and hence, counteracting drought and heat stress in wheat plant [ 40 ]. Flavonoid, 5-hydroxy-7,4′-dimethoxyflavone which was extracted from Combretum erythrophyllum leaves using solvent acetone, inhibited the growth of many Fusarium species including F. graminearum with a MIC value of 0.63 mg/mL [ 41 ].…”

“…After adding the inoculating agent, the randomly selected wheat heads were covered with a plastic bag, which has been removed after 24 h. The plants were then kept for one month before harvesting. All wheat seeds were collected (1.5 g/one wheat head) and ground using a coffee mill (Krups KM75 Coffee Grinder) as described before [ 41 ] and stored in the refrigerator.…”

Lantadene A and boswellic acid isolated from the leaves of Lantana camara L. have the potential to control phytopathogenic Fusarium species

“…A silica gel column was used to separate and purify the fractions as outlined by Seepe et al. [ 43 ]. The column was eluted with 100% petroleum ether as solvent and thereafter, 50 mL of mobile phase mixtures (v/v): petroleum ether: ethyl acetate and ethyl acetate: methanol at different solvent ratio.…”