2012 Annual Report 1a.Objectives (from AD-416): 1) Identify candidate avirulence genes in the wheat leaf rust pathogen, Puccinia triticina, that may condition resistance to wheat leaf rust,. 2)Assemble association mapping population in hard winter wheat and analyze for resistance to leaf rust, stripe rust, and stem rust, and. 3)Construct and analyze mapping populations for resistance to wheat leaf rust, stripe rust, and stem rust. 1b.Approach (from AD-416): Candidate avirulence genes will be identified from gene expression studies or by analysis of genomic sequences of Puccinia triticina. Candidates will be tested for ability to induce hypersensitive necrotic responses on resistant wheat varieties. An association mapping population representing diverse hard winter wheat germplasm will be tested in the field and in the greenhouse for resistance to the three rusts. Lines will be genotyped using a large set of SNP markers. Genomic regions associated with lower mean disease scores will be further investigated. Mapping populations will be developed using the doubled haploid (DH) or the recombinant inbred line (RIL) approach for native and exotic sources of resistance to leaf rust, stripe rust, and stem rust. 3.Progress Report: Work continued on breeding for resistance to Ug99 stem rust of wheat. Three-gene or four-gene combinations of resistance genes Sr22, Sr26, Sr35, and Lr34 are being moved into adapted hard winter wheat backgrounds. Resistance genes Sr32, Sr33, Sr39, Sr40, Sr50, and Sr53 are being backcrossed singly into an adapted hard winter wheat line. Germplasm lines with reduced linkage drag will be identified and genes will eventually be combined in sets of three or four. A mapping population for durable, minor gene, slow-rusting resistance was developed from the spring wheat line, Kingbird, and a susceptible hard white winter wheat. The population was tested in the field for the first time in 2012. As expected, resistance segregated as a quantitative character. In the next year, work will begin on mapping the locations of the stem rust resistance genes in Kingbird. Wheat streak mosaic virus (WSMV) and Triticum mosaic virus (TriMV) are significant pathogens affecting wheat production in Kansas, but there are few resistance genes available for breeding. We are exploring the use of RNA interference (RNAi) to provide resistance to these two viruses. Two homozygous wheat lines with RNAi constructs for the coat protein of each virus have been greenhouse tested for resistance to WSMV and TriMV this year. All four lines were resistant to their respective virus. Future work will include molecular characterization of the transgenic lines.