Identifying genes underlying FHB QTLs in bread wheat

Fusarium Head Blight (FHB) is a destructive fungal disease which reduces wheat yield. Fusarium species produce deoxynivalenol (DON) mycotoxin, which is harmful to animals and humans that feed on contaminated grain. DON acts as a virulence factor enabling fungal spread in the wheat rachis and causing bleaching above the point of infection. Host resistance is broadly used to control FHB and is classified as type I, resistance to the initial penetration, or type II, resistance to fungal spread. Many Quantitative Trait Loci (QTLs) associated with FHB resistance have been identified. FHB resistance QTLs located on the 5A and 2D chromosomes in bread wheat (Triticum aestivum), respectively, were studied in the present project. A recombinant inbred line (RIL) population (Hobbit sib x WEKH85A) and a near isogenic line (NIL) population (Crusoe x Wuhan) were tested for FHB type II resistance to fine-map the 5A and 2D QTLs, respectively. For the fine-mapping of both loci, a single marker analysis based on the physical position of SNPs in the Chinese Spring genome was performed. Results revealed that both 5A (QFhb.WEK-5A) and 2D (QFhb.Wuhan-2DL) loci were stable across years and were refined to 6.24 Mbp on the long arm of chromosome 5A and to 55.6 Mbp on the long arm of the 2D chromosome, respectively. Further fine-mapping is needed to refine QFhb.Wuhan-2DL. Additionally, DON tolerance was assessed using wheat root assays. It was demonstrated that the QFhb.WEK-5A locus in line WEK8H5A may be associated with two traits: DON tolerance and FHB resistance. RNA-Seq identified a DON-responsive candidate gene TraesCS5A02G191700 in the FHB QFhb.WEK-5A locus. Sequencing revealed that a 3 bp (CTT) deletion in the promoter region of gene TraesCS5A02G191700 may be responsible for the enhanced expression of this gene upon challenge with DON or F. graminearum in line WEKH85A. Functionally validation is still needed