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United States Department of Agriculture

Agricultural Research Service

Related Topics

Research Project: Identification and Utilization of Ug99 Resistance Genes from Wild Relatives of Wheat

Location: Cereal Crops Research

2013 Annual Report


1a.Objectives (from AD-416):
The objectives of this cooperative research project are to:.
1)identify Ug99 resistance genes from wild relatives of wheat,.
2)introgress alien species-derived Ug99 resistance genes into wheat, and.
3)deploy Ug99 resistance genes into wheat for the Northern Plains region.


1b.Approach (from AD-416):
Approximately 500 accessions of wild species closely related to wheat and 46 wheat-wild species derivatives will be evaluated for reactions to Ug99 and additional virulent races. The wild species include five diploid Aegilops species with C, D, M, S, and U genomes, four polyploid Aegilops species with the D genome (Ae. cylindrica, Ae. ventricosa, Ae. crassa, and Ae. juvenalis), and five Thinopyrum species (Th. junceum, Th. intermedium, Th. bessarabicum, Th. elongatum, and Th. ponticum). The wheat-wild species derivatives include 23 wheat-Th. intermedium disomic addition lines and 23 introgression lines with small Th. ponticum chromosome segments derived from somatic cell hybridization. They will first be tested for reactions to two African races, TTKSK (Ug99) and TRTTF, and the North American race TTTTF, all with broad virulence spectra at the seedling stage. The genotypes showing resistance to TTKSK will be further characterized with eight races, including three races in the Ug99 lineage (TTKSK, TTKST, and TTTSK), and 3 - 5 North American races (QFCS, QTHJ, RCRS, RKQQ and TPMK). The accessions of the wild relatives identified as resistant to the Ug99 lineage, TRTTF, and TTTTF will be crossed to the durum ‘Rusty’ and common wheat ‘Chinese Spring’. Forty new amphiploids will be synthesized from these crosses using embryo rescue and chromosome doubling techniques. Amphiploids with high levels of resistance will be used to develop alien chromosome addition, substitution, and translocation lines. Stem rust testing and molecular marker analysis will be used to facilitate this introgression process. In addition, about 100 new synthetic hexaploid wheat (SHW) lines will be developed from crosses of Rusty with the Ae. tauschii accessions possessing resistance to the Ug99 races, as well as from crosses of susceptible Ae. tauschii accessions to Triticum carthlicum, T. dicoccum, T. polonicum, T. turanicum, and T. turgidum accessions possessing high levels of resistance to the three races. The SHW lines with high levels of Ug99 resistance will be directly used as donors for developing adapted or elite wheat germplasm through conventional backcross procedures. The currently available Sr genes that are effective against Ug99, including Sr22, Sr25, Sr33, Sr35, Sr36, Sr37, Sr39, Sr42, and Sr45, will be deployed in current durum and bread wheat cultivars adapted to the Northern Plains. Some of these genes have been tagged by molecular markers and/or can be identified using a local pathotype of stem rust; these genes will be directly transferred into the recipients through 3-5 consecutive backcrosses using marker-assisted selection and/or stem rust testing. For the other Sr genes, we will first develop BC1F1 seeds (~30 - 50 seeds for each donor), which will be quickly advanced to BC1F5 through single seed descent. The resistant BC1F5-derived lines will be selected by Ug99 testing. In addition, the resistance genes in one accession from each of the five tetraploid wheat species with high levels of resistance to the Ug99 races, TRTTF, and TTTTF, will be characterized using molecular markers and will be used to develop adapted durum and bread wheat germplasm.


3.Progress Report:

Identification of stem rust resistance genes from wild relatives of wheat. We evaluated 239 accessions belonging to five Thinopyrum species (Th. bessarabicum, Th. elongatum, Th. intermedium, Th. junceum, and Th. ponticum) for their seedling resistance to six U.S. races of stem rust (TMLKC, RTQQC, TPPKC, QFCSC, TCMJC, and TPMKC) in 2012. These accessions were further tested with the three most virulent races TTKSK, TRTTF, and TTTTF in 2013. Results from 2012 and 2013 were similar, with most accessions highly resistant to all races including the three most virulent races. This result suggested that Thinopyrum species are an excellent source of genes for resistance to Ug99 and other races of stem rust. To determine the novelty of the Sr genes, the Ug99- resistant accessions are currently being genotyped using molecular markers closely-linked to the Sr genes (e.g. Sr24, Sr25, Sr26, and Sr43) derived from the Thinopyrum species. Evaluation and characterization of wheat lines and cultivars derived from interspecific hybridization for resistance to Ug99. About 200 hexaploid and tetraploid wheat breeding lines, cytogenetic stocks (wheat-alien species chromosome addition, substitution and translocation lines), and cultivars developed from the hybrids (or their wheat derivatives) between cultivated wheat (durum and common wheat) and related species were evaluated for seedling reactions to the three most virulent races TTKSK, TRTTF, and TTTTF. Seventy-three lines were resistant to TTKSK, with 45 lines being resistant to all three races. The related species involved in the pedigree of these resistant lines, include Th. ponticum, Th. intermedium, Ae. speltoides, Ae. tauschii, rye, Dasypyrum villosum, T. carthlicum, and T. dicoccum. These resistant wheat lines are currently being tested with six additional U.S. races (TPMKC, TMLKC, RKQQC, RHTSC, QTHJC, and MCCFC) and genotyped using the molecular markers closely-linked to the Sr genes derived from Th. ponticum, Ae. speltoides, Ae. tauschii, and T. dicoccum, respectively. Deployment of Ug99 resistance genes into wheat for the Northern Plains region. We continued to introgress Ug99-resistant Sr genes into durum and bread wheat cultivars. In 2013, a total of 32 backcross or cross combinations were made in three classes of wheat (durum, hard red spring, and hard red winter wheat) for eight genes (Sr2, Sr22, Sr25, Sr26, Sr35, Sr36, Sr39, Sr40, Sr47, and Sr-Cad). Five of the Sr genes, including Sr25, Sr26, Sr39, Sr47, and SrCad have been backcrossed to the BC3 generation into hard red spring cultivars Faller and Howard and durum cultivar Tioga. Six intercrosses among the BC2F1 plants with Sr25, Sr26, and SrCad have been produced to stack two or more Sr genes into one cultivar.


Last Modified: 8/22/2014
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