Effects of Solvent Extracted Bioactive Compounds from the Bark, Roots and Leaves of Croton jatrophoides on Tomato Wilt Disease (Fusarium. oxysporum f. sp. lycopersici)

Abstract

Fusarium wilt of tomatoes, caused by Fusarium oxysporum, is a major and most prevalent soil borne disease in tomato plants both in the field and green house. The economic impact of this disease cannot be underestimated. All recommended control strategies have proved to be ineffective in controlling the pathogen. Studies have shown that Croton jatrophoides has medicinal activity against the phytopathogens. This study was conducted to evaluate the efficacy of extracts from Croton 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 extract that could elucidate response against F. oxysporum; to test in-vitro the efficacy and levels of bioactive compounds extracted using selected solvents from bark, the leaves and the root; to determine interaction effects between the treatments and the crude extracts. The experiment involved the isolation of bioactive crude extracts from the roots, bark and leaves of Croton jatrophoides plant using three solvents, namely hexane (non-polar), ethyl acetate (moderately polar) and methanol (highly polar). The isolated crude extracts from each solvent were concentrated using rotary evaporator, then purified using micro-filters. These extracts were then used for testing their antifungal activity in Potatoes Dextrose Agar (PDA) petri-plates containing Fusarium oxysporum inoculum. The results indicated that the quantity of the solvent required for exhaustive extraction of bioactive compounds from the ground material was at 180 mL. The minimum inhibition concentration that elucidated response against F. oxysporum was found to be 50.0 mg/mL. Non-polar solvents such as hexane and ethyl acetate were found to have the highest abilities in extracting bioactive compounds from C. jatropoides materials since most of these compounds that had antifungal activity were non-polar. Hexane derived extracts had the highest significant efficacy in control of Fusarioum oxysporum, comparable to Rindomil, a positive control. Dimethyl sulfoxide (DMSO) had the least effect on Fusarioum oxysporum. In the 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. There were interaction effects between the parts of the plants from which bioactive compounds were derived and the type of solvents used.