Response of indigenous field populations of Fusarium graminearum to fungicide application in Manitoba

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Allen, Sarah
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Fusarium Head Blight (FHB) is an economically important fungal disease of wheat in North America that results in yield loss, reduced grain quality, and grain contamination due to production of mycotoxins by the primary causal species, Fusarium graminearum. Fungicide use is an important component of an integrated pest management strategy (IPM) for the control of FHB, although efficacies have been variable in the field. Field population characteristics, including high genetic diversity, suggest an ability of this pathogen to rapidly adapt to FHB management strategies. This study investigated the impact of fungicide application on the population dynamics of F. graminearum field populations. Across two spring wheat field trials located in Southern Manitoba, isolates were recovered from symptomatic spikes from untreated plots and plots that received a single fungicide application (a 1:1 prothioconazole and tebuconazole mixture) at two application timings. The effect of fungicide treatment on the genetic variation within field populations was assessed using Amplified fragment length polymorphism (AFLP) markers, which showed that fungicide treatment did not have a significant effect on the field population structure within a single growing season. The fungicide sensitivity level of each isolate to the same commercial fungicide product was assessed with an in vitro micro-titre plate method. No significant effect of field fungicide application on the sensitivity levels of recovered isolates was observed, corroborating the genetic data. These data indicate that fungicide application is not significantly impacting F. graminearum field populations in Manitoba within a single growing season. The genetic data identified two subpopulations (previously described as NA1 and NA2) within each field trial that were strongly associated with trichothecene genotype. The fungicide sensitivity level of isolates from the NA2 subpopulation at one site was reduced in comparison to the NA1 subpopulation, but this difference was not observed in the other site. Different agronomic practices between the sites may indicate current management strategies are driving selection for populations with reduced sensitivity to triazole fungicides. Further studies exploring the impact of current management strategies on a wider geographical and temporal scale are required to better understand the population dynamics of F. graminearum to ensure the future sustainability of the management of this important fungal disease.
Fusarium head blight, Fusarium graminearum, DMI fungicide, AFLP fingerprinting, Wheat, Genetic diversity