Differences in sensitivity of Fusarium culmorum towards triazoles and relation with trichothecene chemotypes

Fusarium culmorum is a fungal pathogen causing head blight and foot/root rot on many small-grain cereal as well as ear rot and stalk rot on maize. In addition to yield losses, F. culmorum also produces mycotoxins such as the trichothecenes deoxynivalenol and nivalenol. Triazoles are widely used around the world to control Fusarium spp. but results are not always satisfactory and resistances within the Fusarium genus have been reported. In order to evaluate the triazoles sensitivity of F. culmorum, a collection of 105 strains with different origins, years of isolation, host plants and chemotypes was constituted. The concentrations leading to a 50 % reduction of the optical density (EC50) of those strains towards tebuconazole and epoxiconazole were evaluated using microtiter plate assays. Significant differences of EC50 towards tebuconazole (range = 0.15 to 1.38 mg/l) and epoxiconazole (range = 0.26 to 1.86 mg/l) were observed. Cross-resistance was found between fungicides (ρ=0.6), with tebuconazole being more efficient (mean=0.32 mg/l) than epoxiconazole (mean=0.57 mg/l), although an interaction between the factors ‘strains’ and ‘fungicide’ was noticed. When compared to F. graminearum and F. cerealis, F. culmorum appeared to be the most sensitive species. Interestingly, nivalenol-producing strains of F. culmorum were more resistant to both fungicides compared the deoxynivalenol-producing ones. prix Marasas pour le meilleur poster