Location: Plant Science Research2011 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 2011 several projects related to improving Fusarium head blight resistance in wheat were advanced. First a molecular map of a wheat recombinant inbred population segregating for Fusarium head blight (FHB) resistance from a novel source was developed using several hundred molecular markers. Subsequently, this map was used to identify gene locations controlling FHB resistance in the population. One gene was detected across different disease evaluations in both the greenhouse and field, and accounted for a significant level of the resistance in the population. This gene can be included in FHB breeding efforts to "stack" a series of resistance genes to improve FHB resistance. We completed a project to delineate the genetic basis of improved FHB resistance in a new wheat line that is associated with a new mutation. In this instance, the improved resistance is associated with the loss of a gene or genes that increase susceptibility to FHB. Using a large set of molecular markers, the lost gene(s) were localized with high resolution to the terminal portion of a single wheat chromosome. The mutation also was found to reduce accumulation of the undesired fungal toxin deoxynivalenol. Genes that increase FHB susceptibility may be common in wheat, but this issue remains largely unexplored. We began several projects to investigate the genetic basis of the phenomenon further. This included crossing wheat near-isogenic lines that we believe differ for the presence or absence of a gene that disables a major FHB resistance gene widely used around the world by wheat breeders, and advancing segregating populations toward recombinant inbred status for future genetic studies of FHB resistance gene suppressors. Ultimately, eliminating suppressor genes will increase the overall level of FHB resistance in wheat globally. Multiple disease resistance research projects with the model grass Brachypodium were undertaken in FY 2011. We completed a collaborative project with the University of Modena in Italy to map the locations of genes controlling partial resistance to the leaf rust fungus Puccinia brachypodii in Brachypodium. Three genes contributing partial disease resistance in multiple disease evaluations were identified and their respective locations in the Brachypodum genome identified. Another significant advance was made when a set of Brachypodium genotypes was evaluated for resistance to stem rust of wheat. Seedling responses ranged from immune to susceptible, and a small subset of Brachypodium genotypes included were susceptible to nearly all of the wheat stem rust isolates examined. Plants are now being grown for crossing so that we can proceed with investigating the genetics of wheat stem rust resistance. An important component of the project is to coordinate regional wheat performance nursery programs. This includes the Hard Red Spring Wheat Uniform Regional Performance Nursery and the Uniform Regional Scab Nursery for Spring Wheat Parents. Both were successfully coordinated for the 2010 crop production year, and reports detailing results of the nurseries were prepared and distributed to the breeding community through various web portals.
1. Mapping genes for partial resistance to leaf rust in Brachypodium. The recent emergence of forms of rust fungi that overcome resistance genes used by wheat breeders points to a need to search for alternative methods to control rusts. The model grass Brachypodium has been proposed as a model system for understanding the intricacies of crop resistance to rusts. Along with collaborators in Italy, ARS researchers in St. Paul, Minnesota, determined the chromosome positions of three genes that provide a modest degree of protection to leaf rust disease in Brachypodium. Partial resistance genes are of particular interest because they are believed to retain their ability to protect plants from diseases longer than genes with major effects. Genetically dissecting partial leaf rust resistance in Brachypodium opens avenues for isolating partial rust resistance genes from wheat that can be stacked to obtain durable rust resistance. Such resistance will increase wheat grower profits in the U.S. as well as increase global food security in the face of new aggressive forms of rust.