7a-Acetylugandensolide and antimicrobial properties of Warburgia ugandensis extracts and isolates against sweet potato pathogens

Abstract

7a-Acetylugandensolide together with thirteen known drimane-type sesquiterpenes have been isolated from Warbugia ugandensis bark extracts. Their structures were established by spectroscopic and physical methods as well as comparison with data available in the literature. The in vitro antimicrobial activities of the extracts and isolates were investigated against fungi and bacteria which infect sweet potato. Ethyl acetate extract exhibited the highest (P 0.05) antifungal and antibacterial activities compared to nhexane and methanol extracts. Rhizopus stolonifer was more susceptible to ethyl acetate extract (inhibition zone = 24.5 mm) than Blitox which was used as a positive control. The minimum inhibitory concentration (MIC) for the isolates ranged between 12.5 and 200 mg/ml with the lowest MIC value of 12.5 mg/ml being observed with polygodial against Fusarium solani; warburganal against Aspergillus niger and F. solani; and mukaadial against A. niger.