Fungicide sensitivity towards the predominant pathogen species of Fusarium head blight in cereals from Manitoba, western Canada.

Abstract
In recent years, Fusarium head blight (FHB) is the most aggressive fungal disease and growing threat to
the economic sustainability of cereal crop production in Manitoba due to yield loss and downgrade grain
quality as several mycotoxins contamination occurred in FHB infected grains. In our lab, Fusarium
poae (Fp) and F. graminearum (Fg) were frequently isolated from FHB infected grains of barley and oats.
Four fungicides, namely, caramba (metconazole), prosaro (prothioconazole+tebuconazole), proline
(prothioconazole), folicur (tebuconazole) were tested against representative isolates of Fp (n=13)
and Fg (n=13). These 26 isolates were selected from nearly 300 Fp and Fg strains isolated from
commercial barley and oat fields of Manitoba, based on chemotypes diversity, virulence factors,
mycelial growth performances and genotyping by sequencing (GBS). Fungicide sensitivity was quantified
by measuring the radial growth of the cultures on PDA (potato dextrose agar) media amended at two
concentrations of fungicides (active ingredient: 0.01 and 0.10 mg/L). Two-way analyses of variance
(ANOVA) revealed on average, Fp isolates were statistically less sensitive to all four fungicides,
compared to Fg regardless of doses. Specifically, the redial growth of the Fp-MRC585 strain cannot be
restricted (24%, 5%, 2%, 3% inhibition) by the higher concentration of caramba, prosaro, proline and
folicur amended plates, respectively. Similarly, the Fg-MRC572 strain also cannot be restricted (< 10%
inhibition) to folicur, not the other three fungicides. This study confirmed the Caramba was consistent in
controlling both Fp and Fg isolates tested. This in-vitro assay suggests that the selective pressure exerted
by these commonly used fungicides may impact the population dynamics of FHB species, most likely the
increasing insensitivity towards newly evolving/shifting F. poae communities in the regions due to
different intrinsic characteristics and tolerance ability of these field isolates. The current results would
assist Manitoba small grain producers to select effective fungicides in the integrated FHB management
strategies.