2013 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.
This project terminated during FY13. During the life of the project, significant advances were made in the areas of wheat genetics and genomics, as well as research advancing the model grass Brachypodium distachyon. Analysis of wheat genetic stocks each containing one of five different reported genes for Fusarium head blight resistance derived from diverse wheat varieties and wheat relatives revealed that just one, the well-known gene Fhb1, consistently enhanced resistance. This indicates that the other genes will not be useful for improving resistance to this disease in Midwestern wheat varieties. Molecular mapping of Fusarium head blight resistance in an Australian wheat variety indicated that the resistance in the variety was conditioned by multiple genes with small and inconsistent effects. Surprisingly, a gene with the largest and most consistent effect on resistance came from the susceptible parent in the mapping population that was analyzed. Serendipitously, during this project a spontaneous mutation occurred in one wheat line being developed that resulted in the loss of a specific chromosome segment. Deletion of this segment greatly increases Fusarium head blight resistance, suggesting that one potential reason that improving Fusarium head blight resistance in wheat is so challenging is that genetic inhibitors of resistance genes are present in wheat. Thus, this novel chromosomal deletion may be a useful new tool for improving Fusarium head blight resistance in wheat because it appears to eliminate an inhibitor gene. A second major focus of the project employed the model grass Brachypodium for genomics research. One accomplishment was leading the development of the first molecular map of Brachypodium, which involved collaboration with multiple laboratories in the U.S. and U.K. Similarly, genetic materials developed during the course of the project were used in collaborative research to develop three additional molecular maps of Brachypodium. In two instances these molecular maps were employed to find the chromosome locations of a gene for resistance to a virus that causes damage to barley, and genes for partial resistance to leaf rust of Brachypodium. These discoveries will permit the isolation of the disease resistance genes for use in improving disease resistance in barley and wheat. Mutational analysis of Brachypodium identified mutants with altered resistance to the disease stem rust. One mutant shows a loss of resistance, while another exhibits improved resistance. These mutants can be used to explore how Brachypodium resists infection by wheat stem rust. This will lead to the isolation of key genes that can be transferred to wheat to improve stem rust resistance in this valuable crop. Lastly, a major advance in plant genomics was completed in the form of the development of a high quality whole genome sequence of Brachypodium. This project, for which the SY served as a project co-director, involved a large international collaboration of scientists from the U.S., Europe, and Asia. This genome sequence is being used to accelerate research and crop improvement in wheat, barley, oat, and other crops.
Molecular mapping of a leaf rust resistance gene in wheat. Wheat rust is a significant disease of wheat, and the organism that causes it can rapidly overcome resistance genes. Development of durable leaf rust resistance in wheat may be accomplished by combining genes that each only contributes partial resistance to the disease. ARS scientists in St. Paul, MN, identified a molecular marker for a gene conferring partial levels of resistance to leaf rust in both greenhouse and field studies. This marker can be used by wheat breeders to introduce the gene into new wheat cultivars, to gain an additional layer of protection against leaf rust and in turn increase profits of U.S. wheat growers.