IDENTIFICATION AND UTILIZATION OF UG99 RESISTANCE GENES FROM WILD RELATIVES OF WHEAT
Location: Cereal Crops Research
Project Number: 5442-21000-033-19
Specific Cooperative Agreement
Start Date: Jul 01, 2010
End Date: Jun 30, 2015
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.
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.