|Cai, Xiwen -|
Submitted to: Genes, Genomes, Genetics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 26, 2012
Publication Date: June 1, 2012
Repository URL: http://handle.nal.usda.gov/10113/58111
Citation: Klindworth, D.L., Niu, Z., Chao, S., Friesen, T.L., Jin, Y., Faris, J.D., Cai, X., Xu, S.S. 2012. Introgression and characterization of a goatgrass gene for a high level of resistance to Ug99 stem rust in tetraploid wheat. Genes|Genomes|Genetics. 2:665-673. Interpretive Summary: The races of stem rust belonging to the Ug99 lineage have the potential to devastate world wheat production. Goatgrass is a wild relative of wheat that has genes conferring good levels of resistance to Ug99, but they are difficult to introduce into cultivated wheat. Chromosome engineering, which allows for selection for the smallest segments of goatgrass chromosome, is required to achieve this objective. In this study, we used chromosome engineering techniques to transfer segments of goatgrass chromosomes carrying the Sr47 gene to durum wheat. Our analysis of the wheat lines produced from this process indicated that the goatgrass chromosome actually carried two stem rust resistance genes. One gene conditioned a high level of resistance and was located in chromosome arm 2BL near Sr9. The gene in 2BL, which retained the gene symbol Sr47, was different from any other known stem rust resistance gene. The second gene conditioned a moderate level of resistance and was located in chromosome arm 2BS near Sr39, and this gene was assigned the gene symbol SrAes7t. Based on location and response to several stem rust races, the SrAes7t gene is possibly identical to Sr39. Molecular markers which can be used to select the goatgrass chromatin carrying the two rust resistance genes were identified. Durum wheat lines carrying Sr47 and SrAes7t will be useful resources in wheat breeding for controlling Ug99 and other stem rust races.
Technical Abstract: The transfer of alien genes to crop plants using chromosome engineering has been infrequently attempted in tetraploid durum wheat (Triticum turgidum L. subsp. durum). Here, we report a highly efficient approach for the transfer of two genes conferring resistance to stem rust race Pgt-TTKSK (Ug99) from goatgrass (Aegilops speltoides) to tetraploid wheat. The durum line DAS15, carrying the stem rust resistance gene Sr47 derived from Ae. speltoides, was crossed, and backcrossed, to durum 5D(5B) aneuploids to induce homoeologous pairing. After a final cross to ‘Rusty’ durum, allosyndetic recombinants were recovered. The Ae. speltoides chromosomal segment carrying Sr47 was found to have two stem rust resistance genes. One gene conditioning an infection type (IT) 2 was located in the same chromosomal region of 2BS as Sr39 and was assigned the temporary gene symbol SrAes7t. Based on ITs observed on a diverse set of rust races, SrAes7t may be the same as Sr39. The second gene conditioned an IT 0; and was located on chromosome arm 2BL. This gene, which retained the symbol Sr47, was located in the region carrying Sr9, though an allelic relationship was not established. Allosyndetic recombinant lines carrying each gene on minimal alien chromosomal segments were identified as were molecular markers distinguishing each alien segment. The Sr47 gene confers high-level and broad spectrum resistance to stem rust and should be very useful in efforts to control TTKSK. This study demonstrated that chromosome engineering of Ae. speltoides segments is feasible in tetraploid wheat, and is more successful when transferring genes from subtelomeric or telomeric regions.