Fusarium head blight (FHB) is a major disease in wheat causing severe economic losses globally by reducing yield and contaminating grain with mycotoxins. In Canada, Fusarium graminearum is the principal etiological agent of FHB in wheat, producing mainly the trichothecene mycotoxin, deoxynivalenol (DON) and its acetyl derivatives (15-acetyl deoxynivalenol (15ADON) and 3-acetyl deoxynivalenol (3ADON)). Understanding the population biology of F. graminearum such as the genetic variability, as well as mycotoxin chemotype diversity among isolates is important in developing sustainable disease management tools. In this study, 570 F. graminearum isolates collected from commercial wheat crops in five geographic regions in three provinces in Canada in 2018 and 2019 were analyzed for population diversity and structure using 10 variable number of tandem repeats (VNTR) markers. A subset of isolates collected from the north-eastern United States was also included for comparative analysis. About 75% of the isolates collected in the Canadian provinces of Saskatchewan and Manitoba were 3ADON indicating a 6-fold increase in Saskatchewan and a 2.5-fold increase in Manitoba within the past 15 years. All isolates from Ontario and those collected from the United States were 15ADON and isolates had a similar population structure. There was high gene diversity (H = 0.803–0.893) in the F. graminearum populations in all regions. Gene flow was high between Saskatchewan and Manitoba (Nm = 4.971–21.750), indicating no genetic differentiation between these regions. In contrast, less gene flow was observed among the western provinces and Ontario (Nm = 3.829–9.756) and USA isolates ((Nm = 2.803–6.150). However, Bayesian clustering model analyses of trichothecene chemotype subpopulations divided the populations into two clusters, which was correlated with trichothecene types. Additionally, population cluster analysis revealed there was more admixture of isolates among isolates of the 3ADON chemotypes than among the 15ADON chemotype, an observation that could play a role in the increased virulence of F. graminearum. Understanding the population genetic structure and mycotoxin chemotype variations of the pathogen will assist in developing FHB resistant wheat cultivars and in mycotoxin risk assessment in Canada.
Fusarium head blight (FHB), caused by several Fusarium spp., is a worldwide problem that severely impacts cereal grain yield and poses major risks to human and animal health due to production of the mycotoxin deoxynivalenol (DON) and its acetylated forms, 3-acetyl-DON (3-ADON) and 15-acetyl-DON (15-ADON). Recent studies suggest an inconsistent effect of F. graminearum chemotypes and resistance of wheat (Triticum aestivum) genotypes. To gain insight into the interaction effects of F. graminearum chemotypes and spring wheat genotypes on FHB resistance response, 10 spring wheat genotypes with varying levels of FHB resistance were inoculated with 10 F. graminearum isolates, consisting of 5 3-ADON- and 5 15-ADON-producing isolates and evaluated in type I (spray inoculation) and type II (point inoculation) resistance assays. Wheat genotypes carrying the resistance allele of the Fhb1 quantitative trait locus on chromosome 3BS had lower disease in type II evaluations, regardless of F. graminearum isolate or chemotype. Isolates of F. graminearum were also significantly different for disease aggressiveness. In addition, the 3-ADON-producing isolates were 18% more aggressive than the 15-ADON isolates in type I resistance assays. No difference in aggressiveness of the two chemotypes was observed, when tested in type II resistance assays. There was no interaction effect between F. graminearum chemotypes and spring wheat genotypes, suggesting that screening of germplasm for resistance can be performed with limited number of aggressive isolates.
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