Short reportIn vitro activities of Maesa lanceolata extracts against fungal plant pathogens
Section snippets
Plant.
Maesa lanceolata Forsskal var goulungensis weir (Myrsinaceae) [1], [2] stem bark (500 g) collected from Kakamega forest in Western Kenya and authenticated by Mr Andrew Chapya (a taxonomist affiliated to the University of Nairobi Herbarium). A voucher specimen is held at the Herbarium, in Nairobi, Kenya (Ref. 306/2001).
Uses in traditional medicine.
Fruits of M. lanceolata are widely used in East Africa to treat a variety of ailments, such as sore throat, tapeworms, hepatitis and cholera [3]. In Central Africa, it is used against Entamoeba histolytica infections [4], while in Saudi Arabia a decoction of the heated fresh leaves is used to alleviate rheumatic arthritis [5].
Previously isolated classes of constituents.
Saponins from the leaves [6], benzophenons from the fruits [7]. M. lanceolata extracts are active against Bacillus subtilis [8].
Tested material.
Hexane, chloroform and methanol extracts (yields: 1.02, 1.91 and 2.99%, respectively), 17 fractions obtained by Si-gel CC of the methanol extract eluting with ethyl acetate–methanol, three fractions obtained from fractions 15–17 (yields: 0.005, 0.009 and 0.015%, respectively) above by PHPLC, performed with a C18 column eluting with MeOH–water mixtures (POA detection).
Studied activity.
Antifungal. Dispensed amount of the tested material: 0.25–50 μg.
Micro-organisms used.
Isolated and identified fungal strains stored and maintained by normal sub-culture techniques at Colorado State University (USA) were used for the bioassays. The following fungal isolates were tested: Trichoderma virens, Pythium ultimum, Rhizoctonia solani, Phytophthora cryptogea, Fusarium oxysporium, Aspergillus niger, Phoma sp., Sclerotium rolfsii, Pyrenophora teres and Cochliobolus heterostrophus.
Results.
All 10 fungi tested were inhibited strongly by the methanolic extract (Table 1). Only two fungi (P. ultimum and R. solani) were moderately inhibited.
The methanolic extract was separated through open-air chromatography and 17 fractions were collected and bioassayed. With the exception of fractions 15, 16 and 17, which showed strong inhibitions, the other fractions displayed no activity. Upon pooling the three active fractions together and passing them through HPLC, three peaks were recovered.
Discussion and conclusion.
It was previously reported [6] that M. lanceolata does not have antifungal activity. However, our results clearly show the contrary. One possible explanation for this contradictory result is that we used stem bark instead of leaves [4], [9].
P. ultimum and R. solani were inhibited by methanolic extracts. However, the purified fractions lost the inhibitory activity. This phenomenon is currently observed in natural product separation [4], [6]. A possible explanation is that the compounds in
Acknowledgements
Funding for this research was provided by the Colorado State University (CSU) Agricultural Experimental Station through J.M.V., and the Fulbright Senior Scholar Exchange Program that enabled P.O.O. to undertake this work at CSU. We wish to thank the two Institutions and Mr Andrew Chapya (Taxonomist) who collected and authenticated plant materials.
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