Alberta Grains, Manitoba Crop Alliance, Saskatchewan Barley Development Commission, Western Grain Research Foundation
Fusarium head blight (FHB) is a fungal disease affecting cereal crops in Canada that reduces productivity and produces mycotoxins in the grain. This fungal disease is caused by a number of Fusarium species. In Canada, Fusarium graminearum is considered as the most important Fusarium species because of its abundance, its toxin producing ability and its impact on grain quality and yield. In the last decade, dramatic changes in the proportion of Fusarium species have been noted. Recent studies have identified F. poae as a major Fusarium species complex that causes FHB in grain in several European and South American countries. In Canada, annual FHB surveys indicate that F. poae is the predominant Fusarium species found in commercial barley and oat fields. F. poae can produce a wide range of type A and B trichothecene mycotoxins as well as several non-trichothecene mycotoxins. A thorough understanding of the population structure and chemotype composition of Fusarium species from multiple crops such as wheat, corn, barley and oats is crucial to understanding the fungal complex that causes FHB. The goal of this project is to improve yield and grain quality in Canada by identifying chemotypes of Fusarium species, its distribution and relationship to mycotoxins, and their impact to the grain industry.
Between 2018 and 2023, the surveys for Fusarium head blight (FHB) on barley and oat were conducted annually in Manitoba, Alberta, and Saskatchewan when crops were at the early- to soft-dough (ZGS 79–82) (Zadoks et al. 1974) stages of growth. Grain samples from producer’s fields were analyzed for Fusarium infection using morphological- and molecular-based methods.
Between 2018 and 2023, F. poae and F. graminearum were the two most frequently isolated Fusarium pathogens affecting barley in Manitoba, Saskatchewan, and Alberta.
In Manitoba, F. poae was the predominant Fusarium pathogen detected in between 15.3% to 84% of fields and 1.73% to 18.5% of kernels. In comparison, F. graminearum was detected at a lower level, between 10.5% and 34% of fields and between 0.37% and 2.27% of kernels (Figure 1 and Figure 2). F. poae infection was the highest in 2022, detected in 100% of fields and 18.1% of kernels. F. graminearum infection was the highest in samples from 2020, found in 34% of fields and 2.3% of kernels.
In Saskatchewan. F. poae infection was the highest in 2018 (82% of fields and 7.9% of kernels), whereas the highest level of F. graminearum was found in samples collected in 2020 (60% of fields and 2.1% of kernels).
Fusarium infection was also detected in barley samples collected in Alberta. However, the infections caused by F. poae and F. graminearum were much lower than those from Manitoba and Saskatchewan.
In oat, F. poae, F. graminearum, and F. sporotrichioides were the three most common Fusarium species in oat samples from Manitoba and Saskatchewan between 2018 and 2023.
In Manitoba, F. poae was the predominant Fusarium species detected in oat, found in 54-89% of fields and 5.3-21.1% of kernels. In comparison, the levels of infection caused by F. graminearum and F. sporotrichodies were much lower. The percentage of infection caused by F. graminearum was higher than by F. sporotrichiodies from 2018 to 2020, but they were similar in 2021 and 2022.
In Saskatchewan, F. poae was the predominant Fusarium species detected in oat from 2018 to 2021, found in 49-85% of fields and 5.5-12.6% of kernels. The infection levels caused by F. graminearum is lower than F. poae but higher than F. sporotrichiodies.
The content of Fusarium-associated mycotoxins in barley and oat grains was analyzed using LC-MS/MS. One gram of flour was used to extract mycotoxins.
In Manitoba, average concentrations of DON in samples collected from 2019 to 2021 varied between 12 and 243 ppb. The highest average concentration of DON was found in 2020 samples with a maximum of 4540 ppb. The average concentrations of NIV in barley samples from 2019 to 2021 ranged from 123 to 660 ppb. The highest average concentration of NIV was also found in samples collected in 2020, with a maximum of 5320 ppb. The average concentrations of T-2/HT-2 in samples between 2019 and 2021 ranged between 8-27 ppb with a maximum of 430 ppb, which were much lower than DON and NIV.
In Saskatchewan, average concentrations of DON in samples collected from 2019 to 2021 varied between 8 and 345 ppb. In the 2020 samples, the average concentration of DON was the highest, with a maximum concentration of 5321 ppb. The average concentrations of NIV in barley samples from 2019 to 2021 ranged between 8 and 332 ppb. The highest average level of NIV was also found in samples collected in 2020, with a maximum of 4523 ppb. H2/HT-2 mycotoxins were detected only at a trace level, with the highest average concentrations found in samples collected in 2020.
In Alberta, DON, NIV, and T-2/HT-2 were also detected in samples collected between 2019 and 2021 but only at low levels.
NIV was detected in oat samples at a significant level, especially in samples from 2020. The average concentrations of DON and NIV were similar in samples from Manitoba and Saskatchewan between 2019 and 2021. In both provinces, the average concentrations of NIV were highest in samples collected in 2020 (551 ppb for Manitoba and 584 ppb for Saskatchewan). This result shows the importance of testing for NIV in naturally infected oat grains. At present, the testing for NIV is not routinely conducted at mills or elevators in Canada.
Principal component analysis (PCA) was performed to identify the primary contributors of different Fusarium mycotoxins in oats. The first two dimensions accounted for 53% of the variability using the three most common Fusarium species (Fp, Fg, and Fs) in the grain samples. On the x-axis, component 1 describes 31% of the variability; on the y-axis, component 2 represents an additional 22% of the original variability. A strong correlation was found between Fg DNA and DON as they clustered in the same quadrant. Similarly, Fp DNA, NIV, and BEA showed a close association. Fs and T-2/HT-2 showed the maximum correlation within 3-year sample analyses.
Virulence attribute of F. poae/F. graminearum on wheat, barley and oat
The virulence of F. graminearum and F. poae on Akina(oat), CDC Austenson(barley), and AC Barrie(wheat) was examined in the growth cabinet. F. poae strains MRC 424 and MRC 99 were selected based on the production of APS1 (apicidin biosynthetic) and NRPS (nonribosomal peptide-synthetase) metabolites. F. graminearum strains (MRDC 85 and MRDC 86) were selected based on chemotypes (3-ADON and 15ADON chemotypes).
The pathogenicity of F. poae and F. graminearum on wheat, oat and barley were compared based on the visual estimation of the percentage of Fusarium infected spikelets, the concentration of Fusarium DNA, and mycotoxins in infected grain samples.
Based on the visual symptoms, F. graminearum is more pathogenic than F. poae on AC Barrie (wheat), CDC Austenson (barley) and Akina (oat). Although all three varieties are rated as I for FHB resistance, F. graminearum is more pathogenic on AC Barrie (wheat) and CDC Austenson (barley) compared to Akina (oat). On the other hand, F. poae is more pathogenic on CDC Austenson (barley) and Akina (oat) than AC Barrie (wheat)
The samples were collected at maturity and subjected to qPCR analysis for Fusarium biomass. The concentration of Fusarium graminearum DNA was higher in AC Barrie (wheat) than Akina (oat) and CDC Austenson (barley) when plants were inoculated with F. graminearum. In comparison, the concentrations of F. poae DNA were higher in grain samples of Akina (oat) and CDC Austenson (barley), compared to AC Barrie (wheat), after the inoculation of F. poae. The co-inoculation of F. poae and F. graminearum slightly reduced the concentration of F. graminearum DNA in Akina (oat) and CDC Austenson (barley). In contrast, such a trend was not observed in the concentration of F. poae DNA in those samples (Table 3).
We also investigated the production of Fusarium mycotoxins in the grain samples, including DON, DON3G, NIV, DAS, and BEA. The concentrations of DON and DON3G were higher in grain samples of CDC Austenson (barley) and CDC Barrie (wheat) compared to Akina (oat). In comparison, the concentrations of NIV were higher in CDC Austenson (barley) and Akina (oat) than in CDC Barrie (wheat). Additionally, the co-inoculation of plants with F. poae and F. graminearum resulted in a slightly lower level of DON in grains samples of CDC Austenson (barley) and CDC Barrie (wheat). Still, they did not affect the concentration of NIV in samples of CDC Austenson (barley) and Akina (oat) (Table 4).
Our study shows that F. graminearum and F. poae differ in pathogenicity and host specificity. F. graminearum is more aggressive than F. poae when measured by visual symptoms, Fungal DNA concentrations and mycotoxin levels. F. poae is more pathogenic in barley and oat than wheat. The co-inoculation of two pathogens only caused a slight decrease in the concentration of F. graminearum DNA and DON. In contrast, it does not affect the concentration of F. poae and its associated mycotoxins, including NIV, DAS and BEA.