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Mycotoxin profiles of Fusarium graminearum in corn and wheat in Ontario

Dr. R. R. Burlakoti, Weather INnovations Consulting LP

Fusarium diseases of corn and wheat in Ontario

Fusarium graminearum is an economically important fungal pathogen in corn, wheat and other small grains in Ontario. The fungus causes Fusarium head blight (FHB) of wheat. FHB is problematic in spring and winter wheat as well as other small grains in Ontario. FHB is a historic disease of cereal grains of Canada; the disease was first reported in the late 17th century and has been becoming increasingly problematic since 1890s. FHB epidemics have been occurred several times in last few decades. The fungus also causes Gibberella ear and stalk rot in corn. Gibberella ear rot (GER) is also problematic for Ontario corn production; the GER epidemics in 1996, 2006, and 2011 caused millions of dollars losses to Ontario grain industries. Both FHB and GER diseases reduce the grain quality and marketability and they contaminate grains with mycotoxins. Both diseases are favoured by warm temperature, high humidity and rainfall during the flowering period of crops.

wheat corn
Fusarium head blight of wheat Gibberella ear rot of corn

Mycotoxin production by Fusarium graminearum in cereal grains

Fusarium graminearum produces preharvest mycotoxins in corn and wheat in the field. Incidence of FHB and GER in wheat and corn grains increase the levels of mycotoxins, however, the fungus can also produce mycotoxins without visible symptoms in grains. These mycotoxins cause health hazards to both humans and animals. Among several mycotoxins produced by this fungus, the trichothecene group, primarily deoxynivalenol (DON,) is the major problem in Canadian cereal grains. Canadian Food Inspection Agency has established the maximum tolerable limit for DON 1 ppm for food grains and 3 ppm for livestock feeds.

What are the chemotypes of Fusarium graminearum?

The DON producing F. graminearum strains also produces the acetyl derivatives of DON; 3-Acetyldeoxynivalenol (3ADON) and 15-Acetlyldeoxynivalenol (15ADON), in cereal grains. Compared to natural DON production, the amounts of 3ADON and 15ADON productions are not significant in cereal grains. The F. graminearum strains that produce DON and 3ADON are called ‘3ADON chemotypes’, and the fungal strains that produce DON and 15ADON are called ‘15ADON chemotypes’.

Fusarium graminearum chemotype groups in cereal grains

Why are chemotypes of Fusarium graminearum of concern in cereal grain industry?

Historically, 15ADON chemotype of F. graminearum strains are the most predominant in Canada and USA. The 3ADON producing strains originally dominated in European and Asian countries. In recent years, the 3ADON producing strains became dominant in Atlantic Canada and their frequencies have been increasing in western Canada as well as in the Midwest USA. Several researchers have reported that 3ADON producing strains are now more aggressive and are replacing the 15ADON populations in many wheat growing areas of North America. They further claimed that 3ADON producing strains can produce higher quantities of DON in wheat grains than 15ADON producers. It is not clear why 3ADON producing strains produce higher DON than the 15ADON producing strains. It has been suggested that this recent change in F. graminearum population be taken into consideration in FHB management strategies including resistant breeding programs.

Are the Fusarium graminearum chemotypes in Ontario different than other provinces of Canada?

Weather INnovations recent research work on a large scale surveillance of F. graminearum strains from corn and wheat grain samples showed that the majority of the fungal strains in Ontario are 15ADON chemotype. Types of crop cultivars, weather pattern, and geographic locations showed limited impact on the chemotype distribution of the fungus. The frequency distributions of F. graminearum chemotypes are quite different than Western and Atlantic provinces of Canada and Great Plains of United States where the frequency of 3ADON type has been increasing in recent years.

Why is the population dynamics of Fusarium graminearum important in the management of FHB and Food safety?

Fusarium head blight and DON accumulation in cereal grains is affected by weather variables, agronomic practices, crop genetics, and pathogen populations. Fungal populations may change and adapt to different environments and also might have different toxigenic potentials in producing mycotoxin. Information on F. graminearum populations will be useful to screen wheat, corn, and other small grain germplasms against Fusarium head blight and ear mould. The baseline data on chemotype frequency of the pathogen will be also useful in evaluating risk for Ontario food safety policy development. DONcast®, the weather-based model developed in Ontario to predict the preharvest DON in wheat, incorporates several agronomic and weather variables. We hypothesize that the information on the dynamics of F. graminearum populations would be useful to improve DONcast®. For example, if there is regional variation in pathogen population, regional factors can be incorporated in the DONcast® for better performance of the model. The recent research shows less temporal and regional variations in the F. graminearum chemotypes suggesting that the current DONcast® model in Ontario does not require incorporation of the regional effect.