Improving Fusarium Head Blight Management in Durum Wheat in Saskatchewan

Fusarium head blight (FHB) is one of the most important diseases of wheat in Canada. To manage the disease, farmers rely on an integrated pest management strategy that combines cultural practices (tillage and crop rotation), cultivar resistance and fungicide application at the current recommendation of early anthesis until 50% anthesis (BBCH61-65). Moderately resistant varieties are available in common wheat but not for durum wheat due to lack of resistance in the primary gene pool. The current study evaluated the effect of fungicide application timing and seeding rates on durum wheat affected by FHB; field trials were carried out from 2016 - 2018 at three locations in Saskatchewan. The parameters evaluated were: FHB index, Fusarium-damaged kernels (FDK), deoxynivalenol (DON) accumulation, grain protein content (GPC), and yield. Seeding rate influenced all parameters; the high seeding rate (400 seeds m-2) had higher yield and FHB index, lower DON accumulation and GPC than the low seeding rate (75 seeds m-2). Under extended wet conditions (high FHB risk), all anthesis applications starting at BBCH61 to BBCH69 had a similar effect on FHB index, FDK, DON accumulation, and yield, whereas in years with low disease severity, the BBCH65 application had lower disease (FHB index and FDK) and DON accumulation. The dual application (BBCH61+73) results for FHB index, FDK, and toxin content were similar to the BBCH65 application at all site-years. In North America, the triazole (demethylation inhibitors, FRAC group code - 3) fungicides (e.g., tebuconazole, metconazole, and prothioconazole) are the most effective groups against FHB. I tested 252 Fusarium graminearum isolates collected from western Canada for their sensitivity to tebuconazole, metconazole, and prothioconazole. Phenotyping for fungicide sensitivity of F. graminearum isolates revealed variation in sensitivity to each of the three fungicides. The EC50 of the isolates for tebuconazole, metconazole and prothioconazole was between 0.013 - 0.16 mg L-1, 0.008 - 0.088 mg L-1, and 0.012 - 0.058 mg L-1, respectively. The EC50 values did not differ between trichothecene groups 3-acetyl deoxynivalenol (3ADON) and 15-acetyl deoxynivalenol (15ADON) or year of isolate collection (before/after fungicide registration). A three-year Saskatchewan wide survey of Fusarium spp. conducted between 2014 and 2016 revealed that F. graminearum was the dominant species detected and quantified in infected wheat, followed by F. avenaceum. Among F. graminearum chemotypes, the 3ADON chemotype was found more frequently than 15ADON, while the F. graminearum-nivalenol (NIV) chemotype was absent. This work indicated and re-confirmed that the pathogen profile in Saskatchewan is changing over time. Mycotoxin quantification revealed that 72% of the samples had toxin accumulation >1 μg kg-1. Toxins present were DON, D3G, 3ADON, 15ADON, NIV, T2, and HT2. A weak correlation was detected between F. graminearum DNA and DON levels (R = 0.288, P = 0.008). In the final study in this thesis, I found that all four F. graminearum chemotypes (3ADON, 15ADON, NIV, and NX-2) were pathogenic on wheat and varied in FHB severity, with 3ADON (29.7 ± 3.6) and 15ADON (22.4 ± 2.9) isolates more aggressive than NIV (16.7 ± 2.8) and NX-2 (16.2 ± 3.1) isolates. Significant differences were observed for mycotoxin accumulation among chemotypes, which was highest for 3ADON (14.1 ± 2.26 μg kg-1). All these studies will help to understand pathogen population structure and biology, which will help improve future breeding strategies and FHB management programs to reduce yield losses and mycotoxin contamination