PCR chemotyping of Fusarium graminearum, F. culmorum and F.cerealis isolated from winter wheat in Wallonia, Belgium

Within the pathogen complex responsible for Fusarium head blight (FHB) are some species that can produce mycotoxins that accumulate in the grains, creating a threat to human and animal health. In Europe, type B trichothecenes, especially deoxynivalenol (DON), are frequently found in grain batches. Most of the genes involved in producing these mycotoxins (TRI genes) are grouped in a 12- gene core cluster (TRI cluster). Fusarium graminearum, F. culmorum and F. cerealis possess this cluster, but the presence or absence of certain TRI genes, as well as their functionality, results in a strain capable of producing either nivalenol (NIV) or deoxynivalenol and a related acetylated derivative (3- or 15-ADON). Because of the different levels of toxicity in these secondary metabolites, it is important to have a better knowledge of the population in Belgium in order to estimate the risk posed by Fusarium species occurring in wheat ears. Two multiplex PCR reactions, targeting the TRI3 and TRI13 genes, were used to differentiate the strains of the three species cited above in terms of the possible chemotypes (NIV, 3-ADON and 15-ADON). In all, 105 single-spore strains of F. graminearum, 90 of F. culmorum and 20 of F. cerealis, isolated from winter wheat, were tested. The three chemotypes were identified in the F. graminearum population, with the vast majority of the strains (93%) being of the 15-ADON chemotype. For F. culmorum, the 3-ADON chemotype was prominent (76.6%) and the rest of the strains were of the NIV chemotype. The 20 tested F. cerealis strains could produce only nivalenol. The different proportions of chemotypes in F. graminearum and F. culmorum and the existence mixed-chemotype populations in the field indicate different specificities of the chemotypes in epidemics.