2010 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.
The first genetic linkage map for a Brachypodium recombinant inbred line population was completed in collaboration with ARS scientists at Albany, CA, and university colleagues at the University of California. This was used in a collaborative effort to map a virus resistance gene in the population. Selfed progeny of several Brachypodium putative mutants were tested for stem rust resistance and susceptibility, which identified a set of lines that exhibited germline transmission of mutations affecting stem rust resistance. Crosses between two promising mutants and the parent line were made as a first step toward characterizing the genetics of the stem rust resistance mutations. Several new putative stem rust mutants were also identified. A new recombinant inbred population was increased and employed for stem rust resistance genetic analysis, as were eight F2 Brachypodium populations. Several new stem rust isolates that infect Brachypodium were collected. Hydroponically grown Brachypodium root and shoot tissue were provided to colleagues for use in development of a gene expression atlas. Protocols for Brachypodium transformation were implemented to provide a new tool for lab research.
A set of F2-derived F3 wheat lines segregating for a putative new major Fusarium head blight resistance quantitative trait locus (QTL) was evaluated twice in the greenhouse in FY10. Molecular mapping identified the location of the QTL, but further analysis indicated that the resistance derives from a new mutation in the genome of a susceptible spring wheat. Introgression of the wheat Fusarium head blight resistance gene Fhb1 into triticale was completed by backcrossing. This provides several sets of near-isogenic triticale lines differing by the presence or absence of this gene.
With ARS collaborators at St. Paul, MN, molecular markers in wheat were scored in a population as part of a project to map a gene conferring partial resistance to stem rust. RNA from wheat infected with leaf rust was used for microarray analysis at an early time point in the infection process.
As part of coordinating the Hard Red Spring Wheat Uniform Regional Performance Nursery (URN), a report detailing results of the 2009 nursery was written and distributed (see http://wheat.pw.usda.gov/GG2/germplasm.shtml) and the coordination of the 2010 URN was initiated. Similar efforts were completed for a second nursery coordinated – the Uniform Regional Scab Nursery for Spring Wheat Parents (see http://scabusa.org/pdfs_dbupload/ursn08_report.pdf).
New mutation increases Fusarium head blight resistance of wheat. Fusarium head blight (FHB) causes major economic losses to wheat. ARS researchers at St. Paul, MN, in collaboration with University of Minnesota cooperators, have determined that a new mutation in a wheat cultivar that is normally highly susceptible to FHB converts it to a cultivar that is moderately resistant. Greenhouse tests suggest that this mutation reduces disease symptoms by approximately 50%. This new mutation provides a new resource that, when combined with other genes, may improve FHB resistance in wheat. Reducing FHB damage will eliminate many million dollars of economic losses to U.S. wheat farmers.
Garvin, D.F., Mckenzie, N., Vogel, J.P., Mockler, T.C., Blankenheim, Z., Wright, J., Huo, N., Cheema, J.J., Dicks, J., Hayden, D.M., Gu, Y.Q., Tobias, C.M., Chang, J.H., Chu, A., Trick, M., Michael, T.P., Bevan, M.W., Snape, J.W. 2010. An SSR-Based Genetic Linkage Map of the Model Grass Brachypodium distachyon. Genome. 53(1):1-13.
Bevan, M.W., Garvin, D.F., Vogel, J.P. 2010. Brachypodium distachyon genomics for sustainable food and fuel production. Current Opinion in Biotechnology. 21:211-217.
Vogel, J.P., Garvin, D.F., Gu, Y.Q., Lazo, G.R., Anderson, O.D., Bragg, J.N., Chingcuanco, D.L., Weng, Y., Belknap, W.R., Thomson, J.G., Dardick, C.D., Baxter, I.R. 2010. Genome sequencing and analysis of the model grass Brachypodium distachyon. Nature. 463:763-768.