Abstract
Fusarium graminearum is responsible for production of the mycotoxin deoxynivalenol (DON) on maize and wheat in Ontario, Canada. It has been understood since the early 1980s that in most parts of Canada, the predominant chemotype of F. graminearum is 15ADON, and not the 3ADON chemotype mainly found in Europe and Asia. The discovery of F. graminearum strains that did not produce DON but the structurally related 7-α hydroxy, 15-deacetylcalonectrin (3ANX) and its hydrolysis product 7-α hydroxy, 3,15-dideacetylcalonectrin to (NX) demonstrated that we still have a lot to learn about this well studied but complicated fungus. We conducted a survey of maize and wheat samples from Ontario farms. In the 2015 crop year, we isolated 86 strains and tested a representative subset of 20 using the published genetic probes for assessing genotype. We also developed a targeted LC-MS/MS method for the identification and quantitation of known toxins from this species to determine chemotype. The results showed that 80% of our strains produced some 3ANX in addition to 15ADON and one strain produced 3ANX and no 15ADON. Comparison of chemical data with genotyping revealed that in more than 50% of the cases there was no clear agreement. These data demonstrate the importance of chemical analysis for understanding the toxigenic potential of strains, especially using a LC-MS method that is capable of differentiating 3ADON and 15ADON. For this collection, genotyping of isolates did not produce reliable information on the chemotype. This is the first report of 3ANX toxin production concurrently with 15ADON and suggests that the 3ANX producers in North America likely originated from the 15ADON background.
Highlights
Fusarium graminearum and related species that produce the mycotoxin deoxynivalenol (DON) are important pathogens of maize and small grains in temperate areas worldwide [1,2]
The samples were collected by the Ontario Corn Committee, Kent Corn Committee, experimental plots at the University of Guelph Ridgetown Campus as well as samples collected from annual ear rot and Fusarium Head Blight/ Gibberella ear rot surveys conducted by the Ontario Ministry of Food and Agriculture, and the University of Guelph, Ridgetown Campus
In contrast to the agreement observed in the positive control strains, we found that genotypes based on the literature probes from the systematic collection in Ontario generally did not align with all genetic assays for the positive control strains (Table 1)
Summary
Fusarium graminearum and related species that produce the mycotoxin deoxynivalenol (DON) are important pathogens of maize and small grains in temperate areas worldwide [1,2]. The diseases Fusarium head blight (FHB) and Gibberella ear rot (GER) have been observed for hundreds of years. It was reliably known that grain affected by these diseases contained extractable toxins since the 1930s. F. graminearum chemotypes was not resolved until 1973 by the Japanese scientist Takumi Yoshizawa using strains of F. graminearum isolated from grain that had resulted in human toxicosis [3]. The Japanese strains produced DON via 3, 15-diacetyl-DON to the monoacetate 3-acetyl-DON (3ADON) [4,5]
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