Location: Cereal Disease Lab2013 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:
From the screening of over 3,000 Hordeum accessions to African stem rust race TTKSK, less than 3% were found to be resistant. Six diverse accessions with high levels of resistance were investigated genetically. This group included four barley landraces (Hv501, Hv545, Hv602 and Hv612) originally collected from the alpine regions of eastern Switzerland (Canton Graubünden) and two wild barley accessions (WBDC213 and WBDC345) from Uzbekistan. Inheritance studies with the susceptible parent Steptoe revealed that each accession carried a single gene for seedling resistance to race TTKSK. After demonstrating monogenic inheritance in the resistant accessions, bulked segregant analysis (BSA) was used to define the chromosomal locations of the resistance loci. The linked single nucleotide polymorphism (SNP) markers identified via BSA in the six populations all map to the subtelomeric region of the long arm of chromosome 7(5H) in the 158 to 165 cM interval. This region is coincident with rpg4/Rpg5, a gene complex known to confer resistance to race TTKSK. To further confirm this result, a recently developed sequence tagged site (STS) marker for Rpg5 was used and confirmed the presence of a functional resistance gene in all six accessions. Together, these data indicate that a diverse sample of the few Hordeum accessions found resistant to race TTKSK all carry a previously described resistance gene complex. This work further underscores the genetic vulnerability of barley to African stem rust.