Production and characterization of antifungal compounds produced by tomato plants inoculated with Fusarium oxysporum f. sp. lycopersici Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/zw12z8912

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  • The fungitoxicity of acetone extracts from the xylem of Fusarium wilt disease resistant tomato plants (cv. Jefferson) inoculated with Fusarium oxysporum f. sp. lycopersici was greatly influenced by environmental factors. Extracts obtained from plants 1 h after watering were 4-times more toxic than extracts from plants subjected to water stress for 5 h before extraction, and 10-times more toxic than those from plants after 23.5 h of water stress. Materials from plants extracted at various times during the day exhibited a striking diurnal pattern of antifungal activity. Material from plants extracted at the end of the dark period were the most toxic, and extracts obtained at the end of the light period were the least toxic. The extracts were most toxic to the pathogen in vitro at pH 4.5 and were completely ineffective at pH 6.0 and above. Monogenic resistance of tomato to race 1 of the wilt pathogen was negated by the application of 1% ethanol through the roots. Vascular and foliar disease symptoms were pronounced 15 days after inoculation in ethanol-treated plants, but were absent in ethanol-treated uninoculated plants and in untreated inoculated plants. The pathogen population increased dramatically in inoculated plants treated with ethanol, but remained low and constant in inoculated, untreated plants. By 5 days after inoculation, the fungitoxicity of xylem extracts was very low in ethanol-treated, inoculated plants, but was very high in the untreated, inoculated plants. Similar results were obtained with isolated stem sections treated with ethanol and inoculated with the pathogen. The antifungal compounds in xylem extracts were partially purified and characterized. Chromatography on silica gel, Sephadex LH-20, and Sephadex G-10 resolved four highly antifungal compounds. Sequential thin layer chromatography on silica gel was used to isolate one compound which formed hexagonal orange crystals in cold methanol and melted at 96 C. The isolated compound had strong absorption bands in the visible and ultraviolet spectra, indicating the presence of a π-π conjugated system. No α-tomatine or rishitin could be detected in any extracts, suggesting that antifungal compounds other than these two substances may be involved in wilt disease resistance in tomato.
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