An investigation into the biocatalytic and antimicrobial properties of Eucomis autumnalis Mill. bulbs

[摘要] English: Over the past number of years a renewed interest in the search for natural alternative products, with the aim to replace existing synthetic antimicrobial, herbicidal and pesticidal chemicals in organic crop production systems, was shown. Eucomis autumnalis, a medicinal plant found in South Africa, was used in this study to determine the biostimulatory and antimicrobial properties of a crude bulb extract as well as to evaluate the potential to develop a natural product from this plant. Preliminary screening procedures showed that the crude bulb extract possessed no biostimulatory, but indeed antimicrobial properties.After confirming the in vitro antifungal properties of the crude extract on a number of fungal pathogens, its in vivo activity against Mycosphaerella pinodes, causing Ascochyta blight on peas (Pisum sativum), was also confirmed. Using pea leaves, it was also shown that the crude bulb extract had no phytotoxic effect on the plant tissue even at the highest concentration applied. The collective in vitro and in vivo data obtained supplied the rationale for attempting to isolate and purify the active substance(s) responsible for the antifungal activity.By means of activity directed liquid-liquid extraction, using a series of organic solvents with increasing polarity, most of the antifungal activity was contained in a diethyl ether extractant. Column chromatographic separation of compounds in the active diethyl ether extractant yielded ten combined fractions of which only one showed significant anti-fungal activity against the test organism Sclerotium rolfsii.Subsequently, six active components were isolated from the latter fraction by means of preparative TLC and the chemical groups to which they belonged identified using standard colouring reagents as well as fluorescence under UV light. Due to some compounds having similar Rf-values and tested positive for more than one chemical group, it was clear that all in this fraction were not separated in pure form. However, all active compounds in this fraction tested positive for flavonoids, strongly indicating the presence of this chemical group. Flavonoids are known for their strong antifungal properties.It was concluded from this study that the bulbs of E. autumnalis possess significant antifungal activity to warrant a further investigation into the possibility to utilize this plant in developing a natural fungicide with application potential in agriculture. However, purification of the active substance(s) as well as the elucidation of its(their) molecular structure(s) will be important in order to investigate a possible mechanism of action.

[发布机构] University of the Free State