QTL Mapping for Discovery and Characterization of an Inhibitor of Fhb1 in Hexaploid Wheat (Triticum aestivum)

Abstract

Fusarium head blight (FHB) is one of the most destructive diseases of wheat worldwide, resulting in decreased grain yield and seed quality, and infected grain that is unacceptable for end use due to the presence of mycotoxins, such as deoxynivalenol (DON). Asian sources of resistance have had the most impact worldwide, with the most prevalent resistance gene in many wheat breeding programs being Fhb1, originally mapped in the Chinese variety ‘Sumai 3.’ DON is the primary Fusarium graminearum virulence factor, and Fhb1 has been successful at preventing epidemics due to its dual role in fungal defense and DON detoxification, resulting in both reduction in DON concentration and prevention of disease spread within the grain head. However, during candidate gene investigation, segregating susceptibility occurred in the homozygous presence of Fhb1 in the moderately susceptible variety ‘Bobwhite.’ Other studies have also found resistance conferred by susceptible parents, which along with these candidate gene results, indicate there may be inhibitory genes present in some backgrounds that suppress the effect of FHB resistance genes. This study was conducted to first identify additional regions of the genome responsible for FHB resistance, and then determine if any of these regions could be inhibiting Fhb1. The 260-2 (Sumai 3/Stoa//MN97448 resistant NIL)/Bobwhite population used in the candidate gene study was recreated with separate sub-populations selected for the homozygous presence or absence of Fhb1, and genotyped with the 9K Infinium SNP chip. Quantitative trait loci for resistance and correlated traits (FHB spread, FHB severity, FHB incidence, DON accumulation, visually scabby kernels, 30 head weight, micro test weight, plant height, and heading date) were mapped in each sub-population, and phenotypic analysis indicated polygenic inheritance for all traits. Both populations identified genomic regions coincident with previously reported major genes (Fhb2 and Ppd-D1), as well as a potentially novel QTL on the long arm of chromosome 2A. The Fhb2 and 2A QTL regions were highly significant for FHB resistance and exhibited similar additive effects under both Fhb1 states. The combination of all trials conducted here indicates no interaction between any QTL and Fhb1. Although there is no evidence of resistance gene suppression, the results present a thorough investigation of additive gene action for Fusarium head blight resistance in the context of Fhb1-mediated resistance. Selection for QTL at multiple loci will enable wheat breeders to develop improved Fusarium head blight resistance, especially in the presence of Fhb1.