Location: Cereal Disease Lab2012 Annual Report
1a. Objectives (from AD-416):
This proposed three-year program is aimed at mitigating the threat of wheat stem rust (e.g., Ug99) to the Pakistani wheat crop by supporting research that leads to the introduction of new, disease-resistant wheat varieties. The proposed project will address an urgent need, as failure to maintain a vigorous program aimed at curbing the incidence of virulent wheat diseases would have severe adverse implications for Pakistan’s food security situation. The long-term objective is to increase wheat yields and enhance wheat production with both improved varieties and greater adoption of best management practices. The specific objectives through this SCA are: 1) Characterize wheat stem rust races present in Pakistan; 2) Test advanced/elite breeding germplasm from Pakistan wheat breeding programs with multiple stem rust races at the seedling stage; 3) Identify/provide Ug99 resistant accessions of Aegilops tauschii and tetraploids (T. dicoccum, T. dicoccoides) for development of synthetics; and 4) Provide training for Pakistani plant scientists in advanced wheat genetics, agronomy, and pathology so that they can better participate in the BGRI and can better utilize the expertise of international partners.
1b. Approach (from AD-416):
1. Characterize wheat stem rust races present in Pakistan. Understanding virulence composition and dynamics of stem rust pathogen is important for wheat production and for resistance breeding. Selected stem rust samples collected from trap plots, breeding nurseries and/or production fields that are deemed necessary for race analysis by our laboratory will be forwarded to USDA-ARS Cereal Disease Laboratory under import permit. Upon receiving the samples, we will store them in -80C until our season for processing foreign samples begins in December. We will derive single-pustule isolates for each sample and Pgt race will be described. Selected isolates will be stored in CDL collection for future reference. Race-typing data will be communicated back to collaborators when experiments are completed. Publication of race-typing results should reflect the relative contributions among collaborators. 2. Test advanced/elite breeding germplasm from Pakistan wheat breeding programs with multiple stem rust races at the seedling stage. Germplasm screening is an integral part of cultivar development. Screening with multiple Pgt races will allow the postulation of probable stem rust resistance genes present in the germplasm and will facilitate decision-making on advancing resistant lines/release of cultivars. We will integrate the elite Pakistani breeding lines (approximately 400 lines) into our germplasm screening system for stem rust resistance. The lines will be evaluated against a panel of Pgt races, including the TTKS [Ug99] lineage. Data will be distributed to collaborators in Pakistan. 3. Identify/provide Ug99 resistant accessions of Aegilops tauschii and tetraploids (T. dococcum, T. dicoccoides) for development of synthetics. Expertise in making synthetic wheat is available in Pakistan. At the CDL, we will identify accessions of Ug99 resistant Aegilops tauschii and tetraploids (T. dococcum, T. dicoccoides). 10-20 resistant accessions per species will be provided to collaborators in Pakistan for the development of synthetics. Once synthetics are made, we will characterize the developed material by evaluating against stem rust races with a broad range of virulence. Synthetics postulated to possess novel resistance to TTKSK will be characterized for number and location of novel genes through analyses of mapping populations for resistance to TTKSK and genotyping with molecular markers. Markers linked to novel genes will be used to facilitate the selection of resistance in breeding. 4. Training. Provide training for Pakistani plant scientists in advanced wheat genetics, agronomy, and pathology so that they can better participate in the BGRI and can better utilize the expertise of international partners.
3. Progress Report:
Viable stem rust isolates were recovered from 2 of the 19 stem rust samples provided by collaborators. One single race, RRTTF was identified. Single pustule derived isolates, 11PAK15 and 11PAK05-1, are preserved at CDL culture storage. Among the 14 barberry samples with aecial infection, infection on wheat, barley or rye was not observed in inoculation experiments, even though some samples appeared to be viable based on germination test on agar plates. This may indicate the rust is not of cereal rust type. Further work on these samples will be analyzed using DNA markers. Using races in the Ug99 race group, a panel of 9 US races, a Pakistani race (RRTTF) identified in 2010, and a Yemen race (TRTTF). Resistance genes Sr24 were postulated to be present in several lines. We observed a relatively high frequency of susceptibility to race TTTTF in Pakistan wheat. These data, in combination with field stem rust data from Njoro, Kenya, will enable us to identify Ug99 resistance due to adult plant genes. Wheat lines from Pakistan tested in the 2010-2011 greenhouse season were increased, and the seed was available for planting in the 2012 stem rust nursery.