TRI12 based quantitative real-time PCR assays reveal the distribution of trichothecene genotypes of F. graminearum and F. culmorum isolates in Danish small grain cereals.

Quantitative real-time PCR assays, based on polymorphisms in the TRI12 gene of the trichothecene pathway, were developed to identify and quantify the trichothecene genotypes producing 3-acetyl-deoxynivalenol (3ADON), 15-acetyl-deoxynivalenol (15ADON) or nivalenol (NIV) in the Fusarium graminearum species complex, Fusarium culmorum, Fusarium cerealis and Fusarium pseudograminearum. These assays were applied on a total of 378 field samples of cereal grain of wheat, barley, triticale, rye and oats collected from 2003 to 2007 to study the trichothecene genotype composition in Danish cereals. The three genotypes, 3ADON, 15ADON and NIV were found in all five cereal species, great annual variation in the occurrence of the trichothecene genotypes was evident with considerable variation between the samples. 3ADON was the dominant genotype in barley, triticale, rye and oats while 15ADON was most dominant in wheat. The NIV genotype was found at low levels in most samples. Study of genotype composition within the Danish F. graminearum and F. culmorum population was based on principal component analysis (PCA). PCA revealed that the dominating genotype of F. graminearum in wheat is 15ADON. For barley, the PCA analysis indicated that the F. graminearum population consisted of all three genotypes, and in triticale, the F. graminearum population consisted mainly of 15ADON genotype. F. culmorum/F. cerealis showed correlation to the NIV genotype in wheat and triticale but not in barley. F. culmorum/F. cerealis also showed some correlation to 3ADON especially in wheat and triticale. Selected wheat and barley samples from 1957 to 2000 showed low amounts of F. graminearum and F. culmorum in general but with a dominance of the 3ADON genotype. 15ADON was not detected in these samples, except for very low amounts in the sample representing the years from 1997 to 2000. Detection of low amounts of the 15ADON genotype in these historical samples and the relatively high amounts of 15ADON genotype in 2003 and following years correspond well with the occurrence of F. graminearum and indicates that the 15ADON genotype was introduced along with F. graminearum around 2000. The amounts of the 3ADON and 15ADON genotypes correlated well with the total amount of DON whereas the amounts of NIV genotype correlated well with the amount of NIV in wheat and triticale but not in barley where the results indicate that Fusarium poae may also contribute to the NIV content.