Location: Plant Science Research2012 Annual Report
1a. Objectives (from AD-416):
The overall goal of this research plan is to identify and characterize genes that can be used to improve disease resistance in wheat. Four objectives will address this goal. Objective 1: Use marker-assisted selection to introduce new Fusarium head blight (FHB) resistance into hard red spring wheat. Objective 2: Use transcript profiling and virus-induced gene silencing (VIGS) to identify wheat genes involved in resistance to rust pathogens. VIGS will be completed in collaboration with Steve Scofield, ARS West Lafayette, Indiana. Objective 3: Use the model plant Brachypodium distachyon (Brachypodium) to identify and validate genes involved in stem rust resistance in wheat. Objective 4: Coordinate the Uniform Regional Performance Nursery for Spring Wheat Parents. Wheat improvement is a balancing act because it requires the simultaneous selection of multiple diverse traits to develop superior new cultivars. Two of the three diseases that are subjects of investigation here (FHB, leaf rust) presently cause economic losses to the U.S. wheat crop, while the third disease (stem rust) has the potential to do so. By taking a multidisciplinary approach to improving wheat disease resistance as proposed in this research plan, multiple avenues for protecting wheat against these three diseases will become available. Providing strategies, knowledge, and tools for improving wheat disease resistance, as delineated by the first three objectives, will lead to reduced yield losses attributable to FHB and leaf rust, and will ensure that the potential disease threat from stem rust can be addressed proactively. The fourth objective subsequently provides an opportunity for all spring wheat breeders to evaluate the overall performance of advanced germplasm, including assessment of resistance to FHB, leaf rust, and stem rust, in addition to overall agronomic quality.
1b. Approach (from AD-416):
Wheat is the most widely grown crop in the world and is a major staple crop for humans. Wheat is economically very important to the United States, which ranks third among all countries in wheat production and is the world's largest wheat exporter. Despite its importance as a crop, low prices that are generally paid for wheat grain result in small profit margins for producers. Further, both abiotic and biotic stresses can cause significant fluctuations in U.S. wheat production. Reducing wheat losses associated with the fungal diseases Fusarium head blight, leaf rust, and stem rust will enhance both the stability and profitability of U.S. wheat production. This research project seeks to contribute to the goal of controlling these three diseases by completing integrated genetic, molecular genetic, and genomics research that will further our understanding of genes and underlying molecular processes in wheat that are involved in resistance to each of these diseases. The results of this research will provide both new resources and new knowledge that can be used to increase resistance to each of these three diseases in wheat. This will lead to improved wheat yield and yield stability and will ensure that the U.S. wheat crop is protected against current and future disease threats.
3. Progress Report:
In FY 2012 we advanced several projects related to improving resistance to Fusarium head blight (FHB), to finalize previous research projects, and to set up necessary genetic resources (genetic stocks, mapping populations) for future research. Previously we found that deletion of a segment of chromosome 3D in the rapid-maturing wheat Apogee increased FHB resistance. We completed crosses between the line with the deletion and hard red spring wheat lines that contain the FHB resistance quantitative trait locus (QTL) Fhb1, to begin pyramiding the deletion with this QTL. Through growth chamber disease evaluations we re-confirmed that introduction of Fhb1 into Apogee rarely increases FHB resistance, indicating that it has a gene that suppresses the effect of this QTL. We evaluated a population that was segregating for Fhb1 as well as the hypothesized suppressor gene(s) in Apogee, and results revealed a significant deficiency of resistant individuals consistent with the presence of a segregating suppressor gene in the population. We completed development of two F6:7 RIL (recombinant inbred line) populations that will be genetically fixed for Fhb1 but segregating for background genetic differences including suppressor genes that differ between the parents. These populations will provide us the opportunity to examine the genetics of Fhb1 suppression and subsequently determine the chromosome location of the gene(s) involved. Previously we had undertaken a project to map QTLs for FHB resistance in the Australian wheat breeding line ET3. Surprisingly, the most consistent QTL detected came from the susceptible parent of the mapping population. Thus, we made crosses between this genotype and a set of advanced breeding lines from the hard red spring wheat breeding programs at University of Minnesota, South Dakota State University, and North Dakota State University to begin introducing this new QTL into regional wheat-breeding programs. Previously we conducted genetic analysis of timothy stem rust resistance in a Brachypodium RIL population, and results suggested that a single major gene was segregating, together with modifier genes. In 2012, we devised and then tested a method to rapidly map the location of this gene in Brachypodium. This resulted in the identification of a genome region approximately 1 Mb in size that is likely to harbor the gene. This provides a starting point for fine mapping of the gene and, ultimately, its isolation. We had identified induced mutants of Brachypodium that had either enhanced timothy stem rust resistance or increased susceptibility. Quantification of fungal biomass in these mutants was conducted and revealed that it was significantly higher in the susceptible mutant and significantly lower in the resistant mutant compared to their respective wild type parents. We evaluated the genetic basis of susceptibility in one mutant in an F2 population, and results suggest that the mutant phenotype is conditioned by a single locus.
1. Mapping a gene for barley stripe virus resistance in Brachypodium. The model grass Brachypodium has been proposed as a model system for understanding the intricacies of crop resistance to diseases. With ARS and university collaborators in California and collaborators in China, ARS researchers in St. Paul, Minnesota, mapped the chromosome location of a gene for resistance to barley stripe mosaic virus, which can cause significant yield losses in barley. Unusual biological features of Brachypodium such as its high meiotic recombination rate allowed the gene location to be narrowed to a cluster of just five genes. The gene, once isolated, may provide a new avenue of protecting barley against the virus. Employing Brachypodium as a model for gene discovery will accelerate progress toward enhancing disease resistance and other traits in wheat, in turn increasing wheat grower profits in the U.S. as well as improving global food security.
Barrero, J.M., Jacobsen, J.V., Talbot, M.J., White, R.G., Swain, S.M., Garvin, D.F., Gubler, F. 2012. Grain dormancy and light quality effects on germination in the model grass Brachypodium distachyon. New Phytologist. 193(1):376-386.