Effect of trichothecenes produced by Fusarium graminearum during Fusarium head blight development in six cereal species

Fusarium head blight (FHB) is a complex cereal disease associated with trichothecene production; these mycotoxins are factors of aggressiveness in wheat. Six species ( bread and durum wheat, triticale, rye, barley and oats) were submitted to point inoculations with two isogenic strains of Fusarium graminearum; a wild strain (Tri5+) produced trichothecenes and the mutated strain (Tri5-) did not. The trichothecene-producing strain was generally more aggressive than the non-producing strain, but this varied according to crop species. The difference in aggressiveness was less pronounced in rye, a very resistant species. High resistance levels were observed in oats due to the large spacing between florets. In six-row barley, despite the existence of a moderate Type II resistance, the fungus was often observed to move externally from one floret to another within the dense spike, without penetrating the rachis. Bread wheat had low resistance to the trichothecene-producing strain and good resistance to the non-producing strain. Triticale responded to the strains in a similar way but was somewhat more resistant to both: symptoms on the spikelets and rachis of the triticales were restricted to below the point of inoculation. Durum wheat was susceptible to the trichothecene-producing strain and only moderately resistant to the non-producing strain, which was able to cause serious damage only to this species. Our study confirmed that the role of trichothecenes in FHB pathogenesis differs among species. The failure of the trichothecene non-producing F. graminearum strain to spread within the in florescence of wheat, triticale, rye and barley, and the significant reduction of spread in the durum wheat spike strongly suggested that trichothecenes are a major determinant of fungal spread and disease development in Triticeae.