Aqueous Extracts of Tulbaghia violacea Inhibit Germination of Aspergillus flavus and Aspergillus parasiticus Conidia

Abstract

Aspergillus flavus and Aspergillus parasiticus are important plant pathogens and causal agents of pre- and postharvest rots of corn, peanuts, and tree nuts. These fungal pathogens cause significant crop losses and produce aflatoxins, which contaminate many food products and contribute to liver cancer worldwide. Aqueous preparations of Tulbaghia violacea (wild garlic) were antifungal and at 10 mg/ml resulted in sustained growth inhibition of greater than 50% for both A. flavus and A. parasiticus. Light microscopy revealed that the plant extract inhibited conidial germination in a dose-dependent manner. When exposed to T. violacea extract concentrations of 10 mg/ml and above, A. parasiticus conidia began germinating earlier and germination was completed before that of A. flavus, indicating that A. parasiticus conidia were more resistant to the antifungal effects of T. violacea than were A. flavus conidia. At a subinhibitory extract dose of 15 mg/ml, hyphae of both fungal species exhibited increased granulation and vesicle formation, possibly due to increased reactivity between hyphal cellular components and T. violacea extract. These hyphal changes were not seen when hyphae were formed in the absence of the extract. Transmission electron microscopy revealed thickening of conidial cell walls in both fungal species when grown in the presence of the plant extract. Cell walls of A. flavus also became considerably thicker than those of A. parasiticus, indicating differential response to the extract. Aqueous preparations of T. violacea can be used as antifungal treatments for the control of A. flavus and A. parasiticus. Because the extract exhibited a more pronounced effect on A. flavus than on A. parasiticus, higher doses may be needed for control of A. parasiticus infections.

The action mechanism and biocontrol potentiality of novel isolates of Saccharomyces cerevisiae against the aflatoxigenic Aspergillus flavus

“…Saccharomyces cerevisiae EBF101 and S. cerevisiae 117 exhibited the maximal levels of growth inhibition against A. flavus Z103 with clear zones up to 4Á2 and 3Á5 cm, respectively. Recently, several authors recorded the antagonistic effect of S. cerevisiae against A. flavus (Joannis-Cassan et al 2011;Prado et al 2011;Somai and Belewa 2011). The antagonistic ability of S. cerevisiae might be related to the competition for nutrients and space, direct contact and production of hydrolytic enzymes (Lima et al 2013).…”

Tulbaghia violaceaHarv. plant extract affects cell wall synthesis inAspergillus flavus

“…A previous study (Somai and Belewa ) found that the cell walls of A. flavus and A. parasiticus , two closely related fungi, had undergone morphological changes when exposed to subinhibitory doses of T. violacea plant extract. This appears to be a normal reaction in fungi when exposed to plant extracts and has been reported previously (Rasooli et al .…”

“…). Electron micrographs of spores exposed to the plant extract indicated that the extract induced remodelling of the spore cell wall (Somai and Belewa ). This study expands on the above research by focusing on the effects of the plant extract on A. flavus cell wall specifically by investigating changes in the β ‐(1,3) glucan and chitin production and on the β ‐(1,3) glucan and chitin synthases responsible for their biosynthesis.…”

“…In addition, there are about 25 species of Tulbaghia with T. violacea being the most common and is the most often used plant species in traditional medicine (H. Baijnath, personal communication). Owing to the importance of T. violacea in traditional medicine, its antifungal nature and our finding that T. violacea affects spore germination (Somai and Belewa ), we decided to further develop our studies by investigating the mechanism of action of the plant extract on A. flavus . Thus, the current study determines the effect that T. violacea aqueous plant extract has on chitin and β ‐(1,3) glucan synthesis in A. flavus .…”

The effect of storage and processing on antimicrobial activity of Tulbaghia violacea

“…However, there are considerable discrepancies in the antimicrobial assay results reported. Whereas some authors have found the plant to be completely devoid of antimicrobial activity (McGaw et al, 2000;Bamuamba et al, 2008;Nyila et al, 2012), others have observed significant antimicrobial properties in various Tulbaghia extracts (Motsei et al, 2003;Lindsey and Van Staden, 2004;Thamburan et al, 2006;Nteso and Pretorius, 2006a,b;Buwa and Afolayan, 2009;Belewa et al, 2011;Somai and Belewa, 2011;Jäger and Stafford, 2012;Soyingbe et al, 2013).…”