1a. Objectives (from AD-416)
The long term goal of this project is to reduce losses in wheat and barley yield and quality caused by stripe, leaf, and stem rusts, and assure stable,sustainable wheat and barley production while protecting the environment. Over the next five years we will focus on the following objectives: 1)determine factors influencing epidemic development and host-pathogen interactions for rusts, including to identify and monitor emerging races of stripe rust on a national basis and to improve rust prediction and integrated control; 2)evaluate germplasm and breeding lines of wheat and barley for resistance to rusts,including to support breeding programs in developing cultivars with adequate and durable resistance and to identify new sources and genes of effective resistance to stripe rust; and 3)determine the genomic structure and functional genes of the stripe rust pathogen and molecular mechanisms of plant-pathogen interactions.
1b. Approach (from AD-416)
The prevalence, severity, and distribution of rusts will be monitored through disease surveys in commercial fields, monitoring nurseries, and experimental plots of wheat and barley, as well as wild grasses. Stripe rust races will be identified by testing rust samples on wheat and barley differential genotypes. Rust epidemics will be predicted based on environmental and cropping system factors. Geographic regions where stripe rust can over-winter and over-summer will be mapped by analyzing climatic and cropping data. Disease forecasting models will be developed for various epidemic regions by analyzing historical weather and disease data and tested with rust survey data. Fungicide tests will be conducted to identify new effective fungicides. Germplasms and breeding lines of wheat and barley will be evaluated in greenhouses with selected races and in field plots under natural infections of rusts to support breeding programs. New sources and genes of effective resistance to stripe rust will be identified through germplasm evaluation, genetic studies, and molecular mapping. Molecular markers for resistance genes will be developed using resistance gene analog, microsatellite, and other marker techniques. The genomic structure and functional genes of the stripe rust pathogen and molecular mechanisms of plant-pathogen interactions will be determined through constructing physical and functional gene maps. Fingerprinting and end-sequencing bacterial artificial chromosome (BAC) clones will be conducted to construct the physical map, which will be filled with functional genes identified from cDNA clones of the pathogen. Functional genes will be identified by comparing the sequences of full-length cDNA clones to genes in GenBank databases. Molecular markers will be developed using sequences of functional genes and BAC-ends for studying population structures of the stripe rust pathogen. Genes of wheat and the stripe rust pathogen involved in the plant-pathogen interactions will be identified. Formerly 5348-22000-010-00D (3/07).
3. Progress Report
In 2010, we conducted monitoring and forecasting for stripe rust and provided disease updates to growers in the Pacific Northwest (PNW). Through cooperators in other states, stripe rusts of wheat and barley were monitored throughout the US. As a result of our disease monitoring, accurate forecasting, timely alerts, and advices for disease management, wheat growers implemented fungicide control, which minimized damage under the unusually severe stripe rust epidemic. New models were developed and tested to forecast potential stripe rust damage for the PNW and research were finished to determine stripe rust over-wintering and over-summering regions in the U.S. We completed testing 289 stripe rust samples obtained from 14 states in 2009 and we have finished about 50% of more than 300 samples in 2010 to identify virulence races. From the 2009 samples, we detected 6 barley stripe rust races and 27 wheat stripe rust races, of which two new races were identified for wheat stripe rust. The information on predominant races and distribution is essential to breeding for resistance and disease management. To support breeding programs in the U.S., we tested more than 20,000 wheat and barley entries for stripe rust resistance. The data were provided to breeders for developing resistant cultivars and to growers for choosing resistant cultivars to grow. Growing resistant cultivars in the majority of wheat fields prevented major yield losses in the PNW and other regions. Through our intensive testing, cultivars with durable resistance to stripe rust have been developed. In 2010, we cooperated on the pre-release, final release, and registration of more than 10 wheat cultivars possessing stripe rust resistance with breeding programs in various states. To identify new genes for stripe rust resistance and develop molecular markers, we completed a batched bulk marker screening study and identified more than 20 different stripe rust resistance genes from world wheat germplasm. We have mapped a new gene for durable high-temperature adult-plant (HTAP) resistance to stripe rust. We have selected lines with effective resistance and better plant types for breeding programs to use for developing resistant cultivars. To understand wheat-stripe rust interactions, we have constructed the first custom genechip for the stripe rust pathogen and identified 55 genes of the fungus specifically induced in the compatible interaction and 17 genes in the incompatible interaction using the microarray technique. Using a gene sequencing approach, we obtained the first molecular evidence that the stripe rust fungus has largely different sequences in the two nuclei of its asexual spores. The results reveal major mechanisms of the pathogen evolution. In 2010, we initiated the stripe rust genome sequencing project. We evaluated 23 fungicide treatments to control stripe rust. Effective fungicides were identified. We determined yield losses of 24 winter and 16 spring wheat cultivars grown in the PNW and their responses to fungicides. The data will be useful for registering new fungicides and for advising growers to determine whether or not to use fungicides on cultivars they grow.
1. Wheat and barley germplasms and breeding lines evaluated for resistance to stripe rust. For control of cereal rusts, it is critical to identify more germplasms and to select breeding lines of wheat and barley for resistance. In 2010, ARS scientists in Pullman, WA, evaluated more than 15,000 wheat and 5,000 barley entries for stripe rust resistance. From the evaluation studies, we identified new germplasm and advanced breeding lines with stripe rust resistance. The stripe rust evaluations were provided to breeding programs for eliminating potential susceptible cultivars, and developing new cultivars with adequate resistance. Through our rust resistance evaluation and providing resistance resources and molecular markers for resistance genes, more than 10 wheat cultivars with stripe rust resistance were pre-released, released, or registered by various breeding programs.
2. Identified different genes and mapped one new gene for effective resistance to stripe rust. Growing cultivars with genetic resistance is the most effective, economical, and environmentally friendly approach for control of stripe rust, but there are not many available genes effective against all races of the stripe rust pathogen. It is essential to identify new genes for effective resistance. Using a new batched bulk molecular marker approach developed in our program, ARS scientists in Pullman, WA, identified more than 20 different genes conferring effective resistance to stripe rust in 38 wheat germplasms and developed mapping populations to map these genes. One of the genes was mapped to the wheat chromosome. These genes will be useful for breeding programs to develop resistant cultivars.
3. Developed new wheat germplasms with effective resistance to stripe rust. Resistant germplasms usually have undesirable plant types or unwanted agronomic traits, which may discourage breeders to use in developing new cultivars. In 2010, we planted over 10,000 spring wheat lines selected from progenies of crosses we have used to identify and map new effective resistance genes for further selection. From these lines, ARS scientists in Pullman, WA, selected about 50 lines that were fully resistant, with plant types better than their resistant parental germplasms, and potentially having different resistance genes. This new germplasm will be valuable for breeding programs to develop cultivars with a great diversity of effective resistance genes.
4. Identified genes of the stripe rust pathogen involved in interactions with wheat plants and revealed major evolutionary mechanisms of the pathogen. For sustainable control of stripe rust, it is essential to know important genes in the pathogen and mechanisms of its evolution. ARS scientists in Pullman, WA, constructed a custom genechip for the stripe rust pathogen and used gene sequencing to determine genetic variations among major races. From the studies, we identified 55 genes specifically regulated in the compatible interaction and 17 genes specifically regulated in the incompatible interaction, and identified a process created by mutation as the major mechanism of pathogen evolution. The information leads to a better understanding of the plant-pathogen interactions and evolution of the pathogen.
5. Identified new races and determined frequencies and distributions of stripe rust races. The stripe rust fungus is able to evolve into new virulent races and races also can spread from one region to another to render certain resistant cultivars susceptible. Therefore, it is critical to identify new races, and determine frequencies and distributions of races. In 2010, ARS scientists in Pullman, WA, completed the study to identify races for 289 samples collected from 14 states in 2009. We identified 27 wheat stripe rust races including two new races and 6 barley stripe rust races; and determined the race frequencies and distributions in various epidemiological regions. The results provide guidance for breeding programs to use effective genes to develop resistant cultivars.
5. Significant Activities that Support Special Target Populations
Advice on disease control were provided to growers through disease forecasting, disease updates, field day talks, on-farm visits, phone conversation, and e-mails, which greatly reduced damage under unusually severe epidemic of stripe rust in 2010. The disease management activities directly benefited growers and field consulting companies, many of which have small farms and business.
Griffey, C.A., Thomason, W.E., Pitman, R.M., Beahm, B.R., Paling, J.J., Chen, J., Fanelli, J.K., Kenner, J.C., Dunaway, D.W., Brooks, W.S., Vaughn, M.E., Hokanson, E.G., Behl, H.D., Corbin, R.A., Custis, J.T., Waldenmaier, C.M., Starner, D.E., Gulick, S.A., Ashburn, S.R., Whitt, D.L., Souza, E.J., Bockelman, H.E., Long, D.L., Jin, Y., Chen, X., Cambron, S.E. 2009. Registration of ‘USG 3555’ Wheat. Journal of Plant Registrations. 3(3):273-278.