2012 Annual Report 1a.Objectives (from AD-416): The primary goal of this project it to develop agronomically advanced malting cultivars with broad-based stem rust resistance. This will be accomplished by. 1)developing populations from known sources of stem rust resistance identified in Kenya;. 2)determining the genetics of resistance in segregating populations;. 3)mapping the resistance loci to specific chromosomal regions;. 4)identifying closely linked molecular markers for the loci that can be used in marker assisted selection;. 5)develop a set of markers that will be used for MAS to quickly deploy rpg4/Rpg5 stem rust resistance through marker-assisted backcrossing. 1b.Approach (from AD-416): 25 different populations with various sources of stem rust resistance in cultivated, landrace, and wild barley accessions have been developed. Eight populations will be advanced for genetic and mapping analysis. These populations will be screened for resistance to Ug99 and its variants in seedling tests in the U. of Minnesota BL-3 facility and as adult plants in Kenya. The recently cloned Rpg5 and rpg4 genes (Brueggeman et al., 2008) have been shown to provide resistance to race Ug99 and two of its variants (Steffenson et al. 2009). A set of resistant parents and susceptible elite breeding lines from the Midwest breeding programs will be assembled and the rpg4 and Rpg5 alleles sequenced to identify SNPs that are diagnostic for the resistance alleles. We will develop a set of markers that will be used for MAS to quickly deploy this genetic resistance through marker-assisted backcrossing. Resistant parents and newly developed and presumably resistant backcross-derived lines will be tested by Steffenson for resistance to Ug99 in the BL-3 facility and in Kenya or Ethiopia. Additional backcrossing and marker screening would occur in FY10. Stem rust screening of barley accessions in Kenya supported by this agreement is to be conducted in accordance with the ARS specific cooperative agreement with CIMMYT and the Kenyan Agricultural Research Institute. Sample submission should be coordinated with the ARS designated representatives and the screening results should be made publicly available. 3.Progress Report: More than 3,000 cultivated and wild barley accessions were evaluated at the seedling stage to race TTKSK, and less than 3% exhibited resistant to moderately resistant reactions. These results, together with those showing the presence of the previously reported gene complex rpg4/Rpg5 in the four Swiss landraces highlight the extreme vulnerability of barley to African stem rust races. Additional screening efforts are being made to identify additional sources of resistance to race TTKSK in Kenya and South Africa.