2007 Annual Report
1a.Objectives (from AD-416)
Objective 1: Monitor and characterize races of cereal rust pathogens, particularly the new East African strain, Ug99. Sub-objective 1. A. Characterize races of cereal rust (stem rust–Puccinia graminis and Ug99, wheat leaf rust-Puccinia triticina, crown rust- Puccinia coronata) populations by testing on host differential lines with single genes for rust resistance. Identify races of cereal rusts that represent a threat to the production of wheat, oat, and barley cultivars in the United States. Sub-objective 1.B. Characterize populations of cereal rusts using molecular markers, such as microsatellites and single nucleotide polymorphism, combined with virulence polymorphism, to study race evolution, identify genetically distinct populations, and determine migration patterns of rust genotypes within and between continental regions. Sub-objective 1.C. Determine phylogenetic relationships within and between economically important cereal and grass rust fungi including P. coronata, P. graminis, P. hordei, P. recondita and P. triticina. Objective 2: Identify features essential for cereal rust pathogenesis. Sub-objective 2.A. Characterize avirulence genes and their corresponding gene products from the wheat stem rust fungus, Puccinia graminis. Sub-objective 2.B. Characterize the genome of Puccinia graminis. Objective 3. Identify resistance genes and develop effective strategies for deploying host-resistance genes to control cereal rust diseases. Sub-objective 3.A. Test wheat, oat, and barley germplasm from breeding programs throughout the United States for resistance to stem rust, leaf rust, and crown rust using the prevalent races, and races that have high virulence to rust resistance genes common in released cultivars and breeding lines. Postulate presence of rust resistance genes in seedling tests using specific races of rust. Evaluate lines for adult plant resistance in field plots using a mixture of races with virulence to seedling resistance genes. Subobjective 3.B. Determine the genetic basis of rust resistance in wheat, barley, and oat cultivars and germplasm from the United States and world-wide that have had high levels of durable resistance to the rust pathogens. New rust resistance genes that condition durable rust resistance in cereal germplasm will be identified and characterized for chromosome location. Genes that confer resistance to new races with virulence to commonly grown cultivars will be identified. Resistance genes will be identified in segregating populations by rust infection type and using tightly linked molecular markers.
1b.Approach (from AD-416)
Cereal rust pathogens continuously evolve to overcome existing host resistance genes in wheat, barley, and oats. Cereal germplasm with durable rust resistance, and other control strategies are needed to minimize yield losses due to cereal rusts. Variation in cereal rust populations will be analyzed by assessing virulence polymorphism to important rust resistance genes and by using molecular polymorphism to determine the relatedness and relationships between these populations. Migration patterns of cereal rust populations will be established using virulence and molecular markers. Virulence shifts in cereal rust populations in major cereal-producing areas of the U.S. in relation to use of rust resistance genes will be analyzed. Cereal germplasm with rust resistance will be evaluated in seedling plant tests and in adult plant field tests. Advanced germplasm lines with combinations of rust resistance genes will be selected. Cereal germplasm with durable resistance will be genetically analyzed to determine the identity and expression of the rust resistance genes. A genetic map of P. graminis will be constructed using AFLPs, SSRs, and SNPs. Physical maps of regions with avirulence genes will be developed using BAC and cosmid libraries. Genetic determinants of early infection processes in cereal rusts will be characterized. Crosses will be made with other cereal rust fungi to determine the genetics of avirulence/virulence to important rust resistance genes.
Kolmer, J.A., Long, D.L., Hughes, M.E. 2007. Physiologic Specialization of Puccinia triticina on Wheat in the United States in 2005. Plant Disease. 91:979-984.
Olivera, P.D., Steffenson, B.J., Anikster, Y., Kolmer, J.A. 2007. Resistance of Sharon Goatgrass (Aegilops sharonensis) to Fungal Diseases of Wheat. Plant Disease. 91:942-950.