Quantification of trichothecene-producing Fusarium species in harvested grain by competitive PCR to determine efficacies of fungicides against fusarium head blight of winter wheat

We developed a PCR-based assay to quantify trichothecene-producing Fusarium based on primers derived from the trichodiene synthase gene (Tri5). The pr imers were tested against a range of fusarium head blight (FHB) (also known as scab) pathogens and found to amplify specifically a 260-bp product from 25 isolates belonging to six trichothecene-producing Fusarium species. Amo unts of the trichothecene-producing Fusarium and the trichothecene mycotoxi n deoxynivalenol (DON) in harvested grain from a field trial designed to te st the efficacies of the fungicides metconazole, azoxystrobin, and tebucona zole to control FHB were quantified. No correlation was found between FHB s everity and DON in harvested grain, but a good correlation existed between the amount of trichothecene-producing Fusarium and DON present within grain . Azoxystrobin did not affect levels of trichothecene-producing Fusarium co mpared with those of untreated controls. Metconazole and tebuconazole signi ficantly reduced the amount of trichothecene-producing Fusarium in harveste d grain. We hypothesize that the fungicides affected the relationship betwe en FHB severity and the amount of DON in harvested grain by altering the pr oportion of trichothecene-producing Fusarium within the FHB disease complex and not by altering the rate of DON production. The Tri5 quantitative PCR assay will aid research directed towards reducing amounts of trichothecene mycotoxins in food and animal feed.