EVALUATION OF CROTON JATROPHOIDES (MSINDUZI) EXTRACT AS A SUPPRESSANT AGAINST FUSARIUM OXYSPORUM F. SP. LYCOPERSICI IN VITRO

Abstract

Fusarium wilt of tomatoes, caused by Fusarium oxysporum f. sp. lycopersici, is a major soil borne disease in tomato plants. The fungus enters plant through roots and stem causing wilt disease. It has a big economic impact to farmers. All recommended control strategies have proved ineffective in controlling the pathogen. Studies have shown that Croton jatrophoides has activity against fungal phytopathogens. This study was conducted to assess the ability of extracts from C. jatrophoides to suppress Fusarium oxysporum. Specific objectives were: to extract bioactive compounds from C. jatrophoides for use against F. oxysporum; to determine the minimum inhibition concentration of crude extracts that could elucidate response against F. oxysporum; to test in-vitro efficacy and levels of bioactive compounds extracted using selected inhibition concentration that elucidated response against F. oxysporum ranged from 31.25 mg/ml for Leaf/Hexane extract to 50.0 mg/ml for Bark/Methanol extract. Hexane and ethyl acetate solvents had the highest abilities in extracting bioactive compounds from C. jatropoides. Most of the compounds that exhibited antifungal activity were non-polar. Interaction effects were observed between parts of the plants from which bioactive compounds were derived and the type of solvents used. Hexane derived extracts had highest significant (P < 0.05) efficacy in control of F. oxysporum, followed by Ridomil (metalaxyl and mancozeb), a positive control. DMSO had the least effect on the pathogen. In absence of Hexane, ethyl acetate was the second most suited solvent for extraction of bioactive compounds from C. jatrophoides. Methanol had the least abilities in extraction of bioactive compounds from C. jatrophoides. The study has shown that it is possible to extract bioactive compounds from C. jatrophoides and determine minimum inhibition concentration and efficacy of the bioactive compounds. However, further studies are needed to determine the nature, mode of action, specific phyto-chemical substances involved and actual dose for control of Fusarium oxysporum pathogen. Key words: Croton jatrophoides; F. oxysporium; tomatoes wilt; Minimum inhibition