Location: Plant Science Research2014 Annual Report
Wheat improvement is a balancing act requiring simultaneous selection for multiple diverse traits, including resistance to a range of diseases, to develop superior new cultivars. One of the diseases that is a subject of investigation here (Fusarium head blight, FHB) continues to cause significant economic losses to the U.S. wheat crop, while the other (stem rust) has the potential to do so. The overall goal of this project is to identify and characterize genes that will improve resistance to these diseases in wheat. The proposed approaches for improving wheat disease resistance will generate novel strategies, tools, and knowledge for protecting wheat against both FHB and stem rust that complement current breeding efforts for both diseases. These research activities will be coupled with the coordination of a service activity that permits wheat breeders to evaluate advanced germplasm for agronomic quality and disease resistance. Combining basic and applied research in this manner will ensure that new wheat cultivars continue to retain high yield and quality while also being protected from current and potential disease threats. To achieve project goals, three objectives will be pursued: Objective 1: Develop and evaluate hard red spring wheat with improved Fusarium head blight resistance by mapping and introgressing both a new resistance QTL and a novel genome deletion that increases resistance. Objective 2: Evaluate genotypic background effects on Fusarium head blight resistance expression by examining the genetic control of resistance suppression. Objective 3: Characterize and isolate genes for stem rust resistance from the model plant Brachypodium distachyon for introduction into wheat.
Wheat is the most widely grown crop in the world and is a major staple food 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. Both abiotic and biotic stresses can cause significant fluctuations in U.S. wheat production. Reducing current wheat losses associated with the fungal disease Fusarium head blight, and taking steps to protect the crop against the threat posed by stem rust, will increase both the stability and profitability of U.S. wheat production. This research project seeks to contribute to the goal of controlling these diseases by completing genetic, molecular genetic, and genomics research that will further our understanding of genes and molecular processes that are involved in resistance to these diseases. The results of this research will provide both new resources and new knowledge that can be used to increase resistance to Fusarium head blight and stem rust in wheat. This in turn will lead to improved wheat yields and yield stability for producers and will ensure that the U.S. wheat crop is protected against current and future disease threats.
During FY14, progress was made on a number of research objectives. First, as part of an effort to introduce a potential new gene for resistance to the fungal disease Fusarium head blight into wheat grown in the upper Midwest, we identified a set of genetic markers that we believe are in the immediate vicinity of the resistance gene. These will be examined to determine which is closest to the resistance gene, and thus can be used by regional university wheat breeding programs in Minnesota, North Dakota, and South Dakota to indirectly select for it without the need for labor-intensive and time-consuming disease evaluations. In a related project, we are seeking to enhance Fusarium head blight resistance using a novel strategy – introducing into disease-susceptible wheat a unique deletion of part of a wheat chromosome that dramatically increases Fusarium head blight resistance. We advanced the process of introducing this deletion in an additional generation and are now just two breeding generations away from having material for disease testing in the greenhouse to confirm the efficacy of this novel strategy for disease control. In parallel we are combining a well-known wheat Fusarium head blight resistance gene (Fhb1) with this resistance-enhancing genetic deletion, to evaluate the potential benefit of having both the gene and the deletion present to further reduce disease damage. We advanced this project through two more breeding generations in FY14. Another project is seeking to understand why, in one particular wheat variety, the aforementioned Fusarium head blight resistance gene Fhb1 rarely increases resistance. In just one of several genetic stocks we developed from this variety to contain Fhb1 is increased disease resistance evident. Thus we are examining the genetic basis of this phenomenon in a wheat population segregating for what we believe is a genetic inhibitor of Fhb1. We completed a replicated experimental disease evaluation of this population in spring 2014, which revealed clear evidence of one or more segregating inhibitory genes. The long term goal is to identify the chromosome location of the hypothetical Fhb1 inhibitor gene(s), and then use modern genetic breeding methods to eliminate them from wheat, as yet another novel approach for improving resistance to this major disease. An additional area of research is exploring the molecular control of resistance to the disease wheat stem rust on plant species which it cannot infect. Termed nonhost resistance, this type of resistance is very robust and affords long term protection to the disease. We are employing the model grass Brachypodium distachyon (Brachypodium), a relative of wheat that is a nonhost to wheat stem rust, to identify genes that control the process of nonhost resistance. We completed the genetic mapping of an unusual genetic variant of Brachypodium that allows stem rust of a related forage grass (timothy) to infect it. We narrowed down the number of genes that can be considered responsible for allowing the disease to progress to a set of nine. Future experiments will determine which of the nine genes is allowing the disease to develop. Using the same materials, we also evaluated the genetic control of wheat stem rust. While we intend to complete a second disease test to confirm this first evaluation, it appears that two genes may be involved in susceptibility to wheat stem rust, in contrast to what we observed for timothy stem rust. Our long term objective is to use genes critical to nonhost stem rust in Brachypodium to reconstruct critical components of its nonhost resistance response in wheat. This will provide an additional line of defense against this potentially devastating wheat disease. Lastly, a key aspect of continual improvement of U.S. wheat varieties is rooted in evaluating performance of potential new varieties at multiple locations, to assess adaptation and performance in a range of environments. The USDA-ARS has been a leader in coordinating multisite evaluations for wheat grown around the U.S for many decades. In FY14, a report on the agronomic performance of new potential wheat varieties adapted to the upper Midwest was developed for the 2013 growing season, and made publically available. Breeding programs can use information in the report to identify breeding materials in other programs that would be beneficial to include in their own breeding programs. This will permit continued improvement of wheat in the upper Midwest.
1. New tools to fight an old disease. Stem rust is a potentially devastating disease of many grass crops, including wheat. The fungus that causes stem rust can mutate and thus overcome naturally occurring stem rust resistance genes. Thus new genes that provide long term protection against stem rust would hold great value for protecting wheat against stem rust. In collaboration with ARS colleagues in St. Paul, Minnesota and Albany, California, the chromosome location of a gene that plays a role in providing durable resistance to stem rust was determined with high precision in Brachypodium, a model grass related to wheat. This study provides critical information needed for isolating the gene. Genes in plant species that protect them from stem rust may be used to reconstruct novel pathways for stem rust resistance in wheat and other crops, thus enhancing global wheat production and food safety.
Jeong, D., Schmidt, S.A., Rymarquis, L.A., Park, S., Ganssmann, M., German, M.A., Accerbi, M., Zhai, J., Depaoli, E., Fahlgren, N., Fox, S.E., Garvin, D.F., Mockler, T.C., Carrington, J.C., Meyers, B.C., Green, P.J. 2013. Parallel analysis of RNA ends enhances global investigation of microRNAs and target RNAs of Brachypodium distachyon. Genome Biology. 14:R145.
Graybosch, R.A., Bockelman, H., Garland-Campbell, K., Garvin, D.F., Regassa, T. 2014. Wheat. In: Smith, S., Diers, B., Specht, J., Carver, B., editors. Yield Gains in Major U.S. Field Crops. CSSA Special Publications 33. Madison, WI: American Society of Agronomy, Inc., Crop Science Society of America, Inc., and Soil Science Society of America, Inc. p. 459-487.