Avoiding trade-off when enhancing Fusarium Head Blight resistance of barley

Fusarium head blight (FHB) is threatening barley production worldwide. FHB is of particular concern because the causal fungi produce trichothecene mycotoxins, such as deoxynivalenol (DON), that contaminate grain. Malt is used extensively in the brewing and distilling industries and in a wide variety of foodstuffs. Maltsters place a nil-tolerance for DON in grain. The genetic basis of resistance to FHB in barley is complex and many studies have found a close association between morphological characters and levels of susceptibility. For example, resistance to FHB has been shown to be associated with plant height (PH). Unfortunately, most FHB resistant germplasm identified to date has very poor malting quality traits. We recently identified very high levels of FHB resistance in Chevalier, a heritage barley variety, prized for its malting quality. Significantly Chevalier is tall and more susceptible to mildew than the short modern variety, Tipple which carries the mlo powdery mildew resistance gene. Chevalier became obsolete around 1920, before the discovery of the mlo resistance. The project will investigate the relationships between plant height, resistance to FHB and mildew, accumulation of DON and their impact on agronomic traits including malting quality. This work will also determine whether the FHB resistance of Chevalier can be introgressed into modern malting barley varieties without compromising other important agronomic traits. Aim 1: To identify plant height quantitative trait loci (QTL) that do not influence FHB resistance. We have produced evidence to suggest that the mechanism underlying the PH effect is critical in determining whether there is any pleiotropic effect on FHB susceptibility. It is important to evaluate individual PH loci for their FHB response to identify those that may provide the desired agronomic character without compromising resistance to FHB or DON accumulation. To test this, the student will evaluate characterised barley PH mutants along with their parent lines for resistance to FHB and mycotoxin accumulation in grain. This work will reveal those PH loci most promising for breeding purposes. Furthermore, FHB contaminated and healthy grain from each line will be examined for consequences on malting characteristics. Aim 2. To investigate whether FHB and mlo powdery mildew resistances can occur together in the same variety. The mlo powdery mildew resistance has been widely used in spring barley but it has been reported that lines carrying an allele of the mlo resistance are more susceptible to FHB than those that do not. However only one mlo allele (mlo-5) has been examined and the results may be due to linkage to genes conferring FHB susceptibility originating from the donor of this allele rather than to true pleiotropy. To test this, a series of near-isogenic lines carrying a range of mlo alleles from different sources will be assessed for resistance to FHB and DON accumulation to determine whether this negative association is maintained for other mlo alleles. This work will reveal whether mlo compromises FHB resistance and whether particular alleles might provide resistance to mildew without compromising resistance to FHB. FHB contaminated and healthy grain from each line will be examined for consequences on malting characteristics. Aim 3. Identification of QTL for FHB resistance and other agronomically important traits derived from Chevalier heritage barley. A recombinant inbred population is being developed by crossing Chevalier to Tipple. F1 material is available and the student will use single seed decent to produce a population for phenotyping in the final year of the project. A genetic map will be prepared and QTL mapping undertaken for plant height, FHB and mildew resistance and malting quality. This will identify QTL for FHB resistance and will reveal potential trade-offs between these and other important agronomic traits.