Sudanese Withania somnifera: a potential control agent for plant microorganisms

For centuries plants have been used throughout the world as pesticides, drugs and remedies for various diseases. However, pesticides and drugs in general, tend to be very expensive particularly so for the developing countries. Comparative cost is often the deciding factor in choice of control methods. As a result it can be deduced that direct use of crude extracts or dried plant parts, where possible, would be of great value. This study aimed to evaluate the presence and the activity of the natural products in the Sudanese-chemotype Withania somnifera prior to their direct use as crude extract and/or powdered dried plant-parts in the field. The methanolic extract of the aerial parts of Withania somnifera (L) Dunal (Solanaceae) showed interesting antifungal activity against Fusarium nivale (syn Microdochium nivale) and yielded many withanolides after column and preparative HPLC separation which were guided by this antifungal activity (% inhibition zone). An equal volume of water was added to the concentrated methanol and partitioned with ethyl acetate. The active fraction was chromatographed first on a short silica gel (kieselgel) column. Using the chromatogram and a TLC single-spot analysis the collection was combined in 21 fractions. Then, the active Fraction(s) was re-chromatographed on gel exclusion over sephadex LH-20 in a long column. The active subfractions were then subjected to preparative reversed phase HPLC (Waters 600, multisolvent system) and all tubes were collected in 10 subfractions. The active subfractions were then subjected to preparative reversed phase HPLC (Waters 600, multisolvent system) and each peak was collected manually and, the purified active peaks were then subjected to identification. The structures of Withaferin A and 2, 3-deoxy 3methoxy Withaferin A were determined by NH3-DCI-MS (and MS-MS) and NMR spectroscopy. Against Swiss mice Mus musculus (mouth injection using adaptable syringe) these products showed no acute toxicity up to 20 g plant/kg body weight (the highest dose used). It could be concluded that there are many encouraging aspects regarding the potential for a direct use of such crude extract and powdered dried plant-parts against such plant microorganisms under Sudanese environmental conditions: this plant is widely distributed in Sudan, very rich in withanolides, and the quantity is sufficient e.g. the quantity of withaferin A was estimated in the present work to be more than 40 mg/kg plant material. Additionally, this concentration may indicate that the amount of plant material required would not be high. Furthermore, the preparation of the crude-extract or the powdered form would not be expensive. Moreover, in this study no acute toxicity was recorded up to 20 g plant/kg body weight (the highest dose used). In the foreseeable future, further research is needed to determine activities against broader spectrum of plant local causal organism strains of fungi and bacteria both in the laboratory and the field, the ideal formulation and concentrations for field application.