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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

2011 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

We evaluated 37 wheat-wild species derivatives, including 12 wheat-Th. intermedium disomic addition lines and 23 introgression lines derived from somatic cell hybridization for reactions to Ug99 lineage stem rust races(TTKSK, TTKST, and TTTSK), TRTT, QTHJ, RKQQ, TPMK, and TTTT. Four wheat-Th. intermedium disomic addition lines (Z4, Z5, Z6, and TAI 27) showed a high level of resistance to Ug99 lineage races, TRTT, and all or some local races. Nine introgression lines from somatic cell hybridization were moderately resistant to Ug99 lineage races but susceptible to the other five races. On the contrary, 11 introgression lines were susceptible to Ug99 lineage races but resistant to the other five races. We also evaluated eight Aegilops tauschii accessions for resistance to Ug99 and identified five resistant accessions (CIae 12, CIae 25, RL5271, TA1659, and TA2377). We initiated the introgression of the Sr genes that are effective against Ug99 to durum and bread wheat cultivars. A total of 27 crosses 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, and Sr-Cad) have been made. Eleven BC1F1 have been produced. Fifty-eight new SHW lines have been developed by crossing Ug99 resistant cultivated emmer wheat to Ae. tauschii. We initiated linkage mapping of genes for resistance to Ug99 in Ae. tauschii CIae 25 and SHW line TA4152-60. For mapping the resistance gene(s) in CIae 25, we evaluated 800 F2 plants developed from the cross CIae 25 × AL8/78 for resistance to TPMK and identified 192 susceptible plants. DNA samples have been extracted from 192 susceptible F2 plants. For mapping the resistance gene(s) in TA4152-60, we evaluated doubled haploid population NC60, which was derived from a cross between TA4152-60 and ND spring wheat line ND495, for resistance to TPMK. Preliminary linkage analysis indicates that the resistance gene in TA4152-60 might be Sr13, or a new gene closely linked to Sr13, which is resistant to Ug99. More markers will analyzed/developed to add to the current map around the gene.

We previously evaluated 359 T. dicoccum accessions for resistance to TTKSK, TRTT, and TTTT and identified 81 accessions with resistance to the three races. We initiated association mapping of the resistance genes in T. dicoccum. A total of 181 T. dicoccum accessions have been analyzed using 176 SSR and 9,000 SNP markers. Association analysis between the resistance and markers are currently in progress. In addition, about 160 elite CIMMYT SHW lines and their durum parents have been evaluated for resistance to TPMK and some of the lines showed resistance to the race. DNA has been extracted from these SHW lines and will be used for association mapping of the genes for resistance to stem rust.

ADODR monitoring included personal visitation, email correspondence, and telephone discussions.


Last Modified: 8/21/2014
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