The Effect of Fhb1 and Fhb5 Quantitative Trait Loci in Hard Red Spring Wheat Does Not Depend on Fungicide Use for Managing Fusarium Head Blight in Wheat.

Fusarium head blight (FHB), caused by Fusarium graminearum, is one of the most damaging diseases that affect wheat in Canada. The disease is best managed by integrating host resistance and fungicides, mainly demethylation inhibitors. Research has shown that the effect of fungicides may be dependent on the level of resistance of the cultivar. However, whether the performance of genotypes carrying specific Sumai 3-derived major FHB quantitative trait loci is dependent on fungicide application has not been explored. In our study, the performance of near-isogenic lines (NILs; <1.0% genome/alleles from the resistance donor), carrying Fhb1 and Fhb5 in a hard red spring wheat cultivar CDC Go background compared with a moderately susceptible (MS) genotype, was evaluated with and without one application of metconazole during full flowering. Field experiments were conducted at five site-years in Saskatchewan, Canada, between 2016 and 2017. In both the individual and combined analysis (all trials), we found that the effect of NILs and metconazole in suppressing FHB symptoms and deoxynivalenol (DON) accumulation in the grain was additive. FHB severity was generally low and fungicide efficacy levels, relative to the untreated control, were increased in the MS cultivar than in the NILs carrying Fhb1 and Fhb5, which were least affected by the disease. The results confirm the importance of integrating fungicides with cultivar resistance to reduce FHB and DON, regardless of the presence of those well-characterized resistant genes.