A series of novel methyl sulfone derivatives containing 1,3,4-oxadiazole (thiadiazole) moiety were bioassayed in vitro against Gibberella zeae using mycelial growth rate method. The bioassay results showed that compounds xa202 and xt208 displayed excellent antifungal activity against G. zeae with EC50 values of 3.49 μg/ml and 3.73 μg/ml, respectively. The mechanism for compounds xa202 and xt208 against G. zeaewere studied. After treating with compounds xa202 and xt208 at 50 μg/ml for 24 h, the permeability of fungi cell membranes, the conductivity and the concentration of calcium ions (Ca2+) in mycelial solution showed increasing tendency, while the chitinase content experienced a slight decline initially and then increased rapidly. Compounds xa202 and xt208 were also found to have more potent inhibitory activities against ergosterol biosynthesis than a commercial fungicide, carbendazol. The inhibitory rates for xa202 and xt208 were 32.04% and 55.34%, respectively.
Key words: Gibberella zeae, mechanism of action, conductivity, calcium ions and ergosterol biosynthesis.
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