Location: Cereal Disease Lab2011 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
F2:3 populations were developed from crosses between resistant landraces Hv545 and Hv612, and the susceptible cultivar Steptoe. Segregation data for F2:3 families of both Steptoe/Hv545 and Steptoe/Hv612 closely fit a 1:2:1 ratio for HR:SEG:HS. These data indicate that a single gene controls resistance in both populations. The IT of F1 plants from the Steptoe/Hv545 population was very similar to that of the susceptible parent Steptoe (3-2 vs. 33+), indicating that the resistance gene was recessive. At this juncture, it is not clear whether the genes in the two landraces are new or simply alleles of genes already implicated to impart resistance against race TTKSK—notably the rpg4/Rpg5 gene complex. To resolve this, polymerase chain reaction and sequencing of a small region of Rpg5 indicated that Hv545 and Hv612 contain a functional Rpg5 gene; however, characterizations of rpg4 and other possible genes in the region are still ongoing. Three barley mapping populations were phenotyped for reaction to race TTKSK in seedling assays conducted in the BSL3 greenhouse. Two populations were from crosses with parent lines that were identified as having enhanced resistance at the adult stage in screening as part of the Barley CAP in Kenya. A third population was constructed from lines identified as resistant in the Barley CAP as well as parents, progenies, and siblings. This population will be used for a family-based association analysis. The two bi-parental populations did not segregate for seedling reaction. All of the populations have been planted in an adult plant nursery in South Africa. Regular e-mails, telephone calls and meetings were used to plan and coordinate the project.