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Chemotype changes in the Fusarium graminearum population in Canada
In 2004 a paper was published by O’Donnell, Ward, Geiser, Kistler and Aoki proposing to divide the species known as Fusarium graminearum into several species based on phylogenetic analysis of DNA sequences. Subsequent analysis of Canadian isolates by the senior authors demonstrated that in Canada only one of the proposed species is found, and that species retained the name Fusarium graminearum. Further work on these Canadian isolates also revealed a number of other characteristics. Those results have been published in the journal Fungal Genetics and Biology. The title of the paper is "An Adaptive Evolutionary Shift in Fusarium Head Blight Pathogen Populations is driving the Rapid Spread of More Toxigenic Fusarium graminearum in North America" and is authored by T.J. Ward, R.M.Clear; A. Rooney, K O'Donnell, D. Gaba, S. Patrick, D. Starkey, J. Gilbert, D. Geiser, and T. Nowicki. The following information was obtained from that publication.
In North America, the F. graminearum chemotype traditionally responsible for fusarium head blight is known as the 15 ADON chemotype. It forms deoxynivalenol (DON) and its analog 15 acetyl-deoxynivalenol (15 ADON). A second chemotype known as 3 ADON forms DON and 3 acetyl-deoxynivalenol (3 ADON) and has been important outside of North America. As part of a collaborative effort, isolates of F. graminearum collected by the Canadian Grain Commission from Fusarium-damaged kernels of wheat between 1984 and 2004 were analysed by scientists at the United States Department of Agriculture in Peoria using a multilocus genotyping assay for Fusarium species and chemotype determination. The following graph shows the observed change in the population’s chemotype over 6 years in western Canada.
3 ADON Population Shift
With this unexpected and rapid shift in the population, isolates from Prince Edward Island and Quebec were also obtained and analysed. Analysis of these isolates found the 3 ADON chemotype to be well established in those provinces, especially Prince Edward Island where it was the sole chemotype detected. Phenotypic differences, such as toxin producing ability, were compared between 75 isolates, 25 isolates of each of the 3 ADON and 15 ADON populations from western Canada and the 3 ADON population from Prince Edward Island. The isolates were inoculated onto autoclaved rice and analysed for DON, 3 ADON and 15 ADON. Surprisingly, there was a large difference in the DON levels of the 3 ADON compared to the 15 ADON populations.
DON production in vitro
When the ratio of 15 ADON to 3 ADON isolates from the sampled provinces was compared, it showed a strong chemotype cline or gradient, with the 3 ADON population highest in the east and declining in a westerly direction.
Chemotype Changes in the Fusarium graminearum population in Canada, 1998 - 2004
This recent and rapid shift in the F. graminearum population in Canada must be driven by a fitness advantage in the 3 ADON population. At present, collaborative work with colleagues in the Canadian Grain Commission, Agriculture and Agri-Food Canada, and the United States Department of Agriculture in Peoria, assisted by a grant from the Western Grains Research Foundation, is seeking to understand the mechanism and its implication for mycotoxin levels in grain. Interestingly, the observed changes in population and differences in toxin producing potential have also been reported in the Midwest United States. Recently published work by Gale et al. (in press) mirrors the findings in Canada.
