Project Number: 3640-21220-021-00
Project Type: Appropriated

Start Date: Apr 11, 2012
End Date: Apr 10, 2017

Objective:
Objective 1: Monitor, collect, and characterize U.S. cereal rust pathogen populations. Sub-objective 1.A. Monitor, collect and characterize cereal rust pathogen populations in the U.S. for virulence phenotypes to rust resistance genes in cereal cultivars. Sub-objective 1.B. Determine levels of genetic variation in P. triticina and P. graminis populations. Sub-objective 1.C. Refine phylogenetics and systematics of P. graminis and P. triticina. Objective 2: Discover and characterize fungal genes that are involved in pathogenesis and the obligate biotrophic interactions of cereal rust pathogens and their hosts. Objective 3: Identify and characterize rust resistance genes in novel and elite germplasm to assist in the development of resistant cereal cultivars. Sub-objective 3.A. Evaluate wheat, oat and barley germplasm from U.S. breeding programs for rust resistance. Sub-objective 3.B. Identify and characterize new sources of rust resistance in wheat, barley, and oat. The proposed research objectives are central to the mission of the USDA ARS Cereal Disease Laboratory (CDL): to reduce losses in wheat, oat, and barley to major diseases using host resistance. Research is focused on genetic variation in both the host cereals and their rust pathogens that determine the resistance/susceptible phenotype of the interaction. Isolates of rust fungi obtained from annual surveys of the wheat, barley, and oat crops are used to inform the breeding process. Successful control of cereal rusts with host resistance cannot be achieved without knowledge of variation in cereal rust populations. Studies of virulence and molecular variation in cereal rust populations can answer questions that range from the applied, such as which host resistance genes are effective against the current rust population and what resistance genes are in current cereal cultivars, to more basic questions like what are the origins of new races and how do they spread. Discovery of the molecular determinants of pathogenesis and obligate biotrophy in cereal rust fungi via genomic approaches offers intriguing leads in the development of novel resistance mechanisms. Identification, characterization, and introgression of new host resistance to cereal rusts are key to increasing the diversity of resistance genes in our cereals and staying ahead of these "shifty" pathogens.

Approach:
Cereal rust fungi are dynamic leading to constant changes in the U.S. population which leads to the erosion of effective rust resistance in cereal crops. In addition, the introduction of foreign isolates, such as Ug99, further threaten cereal production. Development of cereal cultivars with effective rust resistance and management strategies of these diseases will depend on the monitoring and characterization, virulence phenotypes and molecular genotypes, of cereal rust pathogen populations. Rust resistant cereal germplasm will be selected by testing wheat, oat, and barley lines from breeding programs throughout the United States for resistance to Puccinia coronata, P. graminis, and P. triticina, using the prevalent races, and races that have high virulence to rust resistance genes common in released cultivars and breeding lines. Testing with selected isolates of the cereal rust pathogens and host genetics studies will identify the rust resistance genes in breeding lines and germplasm. Advanced germplasm lines with combinations of rust resistance genes will be selected. Rust fungi produce a large arsenal of effector proteins in order to infect and colonize the plant host. Genetic and genomic approaches will be used to identify and characterize effector genes from P. graminis.