2013 Annual Report
1a.Objectives (from AD-416):
1. Characterize wheat stripe rust races present in Pakistan.
2. Evaluate advanced/elite breeding germplasm from Pakistan wheat breeding
programs with Pakistan stripe rust races at the seedling stage in the
greenhouse and with natural U.S. populations in the field.
3. Provide training to Pakistani students and scientists in stripe rust research.
1b.Approach (from AD-416):
1. For developing cultivars with effective and durable resistance to stripe rust, it is essential to understand virulence compositions in the pathogen populations and dynamics of virulences. To obtain such information, stripe rust will be monitored by Pakistani scientists in commercial fields and disease and breeding nurseries during the wheat growing season. Stripe rust infected leaf samples will be collected and send to the ARS Wheat Genetics Unit at Pullman, Washington for characterizing virulences and identifying races. We will accept up to 50 samples. Upon receiving the samples, we will start to increasing spores if possible. Our standard procedures will be used to recover stripe rust, increase spores and test on differentials. Our newly established set of 20 single-gene differentials will be used for testing every isolates. To identify genetic changes that may not be detected by the stripe rust resistance genes in the differentials, we will extract DNA from spores of the Pakistan isolates. Our recently developed molecular markers (EST-SSR) will be used to characterize the isolates to identify new genotypes and determine genetic relationships among isolates.
2. To help Pakistani scientists in developing wheat cultivars with effective and durable resistance to stripe rust, we will evaluate advanced/elite breeding lines of wheat developed or used by Pakistani breeding programs. Wheat lines will be tested with selected U.S. and Pakistan stripe rust races in the seedling stage under controlled greenhouse conditions. We will also test the Pakistan wheat lines in field under natural infection of stripe rust at Pullman and Mt. Vernon, WA. Comparison of stripe rust data of field and greenhouse tests will allow preliminarily determining the presence or absence of high-temperature adult-plant (HTAP) resistance in the wheat lines. To clarify postulated genes, we will use molecular markers that are available for many stripe rust resistance genes or QTL. Our focus will be on genes and gene combinations conferring effective resistance. For wheat germplasm that potentially have new genes for effective resistance based on all above tests, we will conduct genetic and molecular mapping studies to identify the genes and develop markers to be used in marker-assisted selection.
3. To sustain long-term efforts of improving wheat for rust resistance, students and scientists need to get first-hand experience with stripe rust. We plan to provide training to 2-3 Pakistani scientists and students. Our training will focus on all aspects related to disease monitoring, race identification and survey, germplasm screening, genetics and molecular mapping of resistance genes, and molecular characterization of stripe rust populations.
In 2013, progress was made on all three Objectives. Under Objective 1, we completed tests of 17 recovered isolates from the 2012 Pakistan stripe rust samples. The infected leaf samples from Pakistan were used to inoculate a susceptible wheat variety to recover and increase spores. Each isolate was tested on seedlings of a set of 18 resistant single-gene lines to characterize its virulence pattern. From the 17 isolates, 14 races were identified, of which 7 were not identified previously. These results agree with previous results from our program that the Pakistan stripe rust population has a high virulence variation. In July, 2013, we received 41 stripe rust samples from Pakistan and are currently recovering the samples for identifying races. In August 2012, we received 835 wheat accessions from the ARS Small Grains Collection, which were originally collected from Pakistan, for characterization of stripe rust resistance. These lines were tested with 4 selected U.S. stripe rust races and 3 Pakistani races in seedling stage under controlled greenhouse conditions and also tested under natural infection in the field near Pullman, Washington. From these germplasms, we identified 35 (4.2%) accessions resistant in all greenhouse and field tests, 67 (8.0%) accessions resistant in all race-seedling tests, and 254 (30.4%) with possible high-temperature adult-plant (HTAP) resistance by comparing the seedling tests and adult-plant test in the field. We also tested 220 wheat lines received in 2008-2010, 324 lines received in 2011, and 422 lines received in late 2012 from Pakistan in two field locations, Pullman and Mt. Vernon, Washington, in 2013. Before planting the 2012 wheat nursery, the lines had been grown in a greenhouse during the 2012-2013 winter season to fulfill the plant quarantine requirement. From these materials of mostly breeding lines, we identified 31-82% of the lines with good resistance to stripe rust. The data of wheat lines from different years also indicate a great improvement of stripe rust resistance in Pakistan wheat breeding programs. F2 populations of three crosses made with Pakistani resistant wheat germplasms were tested in the field and advanced to F3 for identifying and mapping genes for useful resistance to stripe rust. Under Objective 3, we continued providing guidance to previous collaborators, current collaborators, and other Pakistan scientists working on rusts through e-mails and visits. An ARS scientist from Pullman, Washington, visited several Pakistan agricultural research institutes in March, 2013 and solved several issues in their rust research. In July, a Pakistan scientist visited our program to gain stripe rust knowledge and learn research techniques.