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.
3. Progress Report:
In 2012, progress was made on all three of the parent project objectives. Under Objective 1, we completed a study to characterize 46 stripe rust isolates from Pakistan together with isolates from other countries. 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 20 wheat genotypes (old differentials) and a set of 20 resistance single-gene lines (new differentials) to characterize its virulence pattern. From the 46 isolates, 42 races were identified using the old differentials and 28 races were identified using the new differentials. These results were sharply different from previous reports of few races in Pakistan and revealed much higher virulence variation in the Pakistan stripe rust population. The stripe rust isolates were also characterized using 20 microsatellite markers. From the 46 isolates, 43 genotypes were identified. The molecular markers detected two major genetic groups and a third genetic mix group. All of the three groups were detected in Pakistan. Both virulence and marker data revealed a relatively high diversity in the Pakistan stripe rust populations compared with many other countries. In 2012, we received close to 200 samples from Pakistan and were able to recover about 10% of the samples due to the reduced quality from mailing. These samples are under virulence testing and molecular characterization. Under Objective 2, we completed the data analysis and report for the Pakistan wheat germplasm we received before 2011 and tested in the field and greenhouse in 2011. For the “2011” Pakistan nursery received indirectly from the ARS Plant Science Unit at Raleigh, North Carolina in September, 2011 and the “2012” Pakistan nursery received directly from Pakistan with a total of 553 lines, we tested them with 4 US and 2 Pakistan races at seedling stage under the controlled greenhouse conditions. For the “2012” nursery, we grew them and inspected new seeds in the greenhouse during the 2011-2012 winter. In the spring 2012, we planted both “2011” and “2012” Pakistan wheat nurseries at Pullman and Mt. Vernon. Stripe rust data were collected and now under analysis. Lines with good resistance to stripe rust were identified and we made several crosses in the field for developing genetic populations to identify and map the resistance genes. Under Objective 3, I continued providing guidance to previous collaborators, current collaborators, and other Pakistan scientists working on rusts through e-mails. From July 16 to August 2, five Pakistani scientists from the National Agricultural Research Center, Punjab Wheat Research Institute, and Barani Agricultural Research Institute visited our program. They were trained in stripe rust research and molecular techniques. This research supports parent project 5348-22000-015-00D objectives 1, 2, and 3.