Anti-fungal, anti-mycotoxigenic activity and phytochemical spectra of selected South African plants

Abstract

Inhibition of in vitro mycelial growth against six mycotoxigenic fungal pathogens in vitro of six medicinal plants leaves extracts to check potential of anti-mycotoxigenic activity . Organic extract from Strychnos mitis exhibited a noteworthy antifungal activity yielding lowest minimum inhibitory concentration (MIC) value of 0.01 mg/ml against three Furasium species (Furasium vercitilloides, Furasium oxysporum and Furasium graminareum) and a further MIC value of 0.08 mg/ml against Aspergillus parasiticus, Aspergillus flavus and Aspergillus ochraceous at 24 hr incubation period. At both 24 and 48 hr incubation period, aqueous extract from Mystroxylon aethiopicum yielded MIC value of 0.02 mg/ml against A. parasiticus while aqueous extract from Spirostachys africana exhibited MIC values of 0.04 and 0.02 mg/ml against F. vercitilloides and F. graminareum at 48 hr respectively. In the mycelial growth inhibition (MGI) studies, the extracts showed varying degree of inhibition in a dose dependent manner. M. aethiopicum showed the highest mycelial growth percentage inhibition of 44.38 against Fusarium verticiloides in a three-day incubation period. Furthermore, the organic extracts were also evaluated for cytotoxicity effects against both African green monkey (Vero) and Bovine dermis (skin) cell lines using the MTT (3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide) assay. Organic extract from S. africana exhibited the lowest lethal concentration (LC50) value of 0.10 mg/ml against both cell lines used in the study, while S. mitis exhibited the highest selectivity index (SI) value of 88.0 against F. graminareum. In the antioxidants assays, only extracts from S. africana and M. aethiopicum exhibited a noteworthy activity against 2,2-Diphenyl-1-picrylhydrazyl (DPPH), 2-2′-Azino-di-[3-ethylbenzthiazoline sulfonate (ABTS) and chelation of iron.The extracts, with potent biological activity, were also subjected to Gas-chromatography-mass spectrometry (GC-MS) analysis to identify the presence and prevalence of phytocompounds. M. aethiopicum extract exhibited the presence of tetradecane (15.74%) and heptadecane (14.96%), while S. africana yielded n-hexadecanoic acid (12.14%) and nonadecane,2-methyl (12.14%). These results suggest that bio-compounds from plants can be further explored in vivo and used to develop a bio-fungicide with less side effects compared to synthetic fungicides. Elsewhere, tetradecane, heptadecane and n-decanoic acid were reported to inhibit the mycelial growth inhibition of various mycotoxigenic fungal strains.