Location: Hard Winter Wheat Genetics Research Unit
Title: Simultaneous transfer, introgression and genomic localization of genes for resistance to stem rust race TTKSK Ug99 from Aegilops tauschii to wheat Authors
Submitted to: Theoretical and Applied Genetics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: January 9, 2013
Publication Date: February 3, 2013
Citation: Olson, E., Rouse, M.N., Pumphrey, M.O., Bowden, R.L., Gill, B., Poland, J.A. 2013. Simultaneous transfer, introgression and genomic localization of genes for resistance to stem rust race TTKSK Ug99 from Aegilops tauschii to wheat. Theoretical and Applied Genetics. 126:1179-1188. Interpretive Summary: Wheat production worldwide is threatened by stem rust. On susceptible varieties, this disease can cause severe crop loss. New races of wheat stem rust have been found over the past decade that can infect most of the wheat cultivars in the US and around the world. To address the need for resistance to this pathogen, previous studies were conducted to survey wild relatives of wheat for resistance and several promising sources of resistance were found. In this current study, two accessions of the wild wheat relative, Aegilops tauschii, were directly crossed with wheat and resistant plants recovered. The resistant plants were then crossed again to wheat to recover more desirable plant types and resistant plants were identified and selected. In the process of introgressing the new resistance genes into desirable wheat lines, populations were developed that enabled the genetic mapping of there resistance genes to identify where they are located in the genome. DNA markers were identified that are linked to the resistance genes and can be used for “marker-assisted selection” in wheat breeding.
Technical Abstract: Wheat production is currently threatened by widely virulent races of the wheat stem rust fungus, Puccinia graminis f. sp. tritici, that are part of the TTKSK (also known as ‘Ug99’) race group. The diploid D genome donor species Aegilops tauschii (2n=2x=14, DD) is a readily accessible source of resistance to TTKSK and its derivatives that can be transferred to hexaploid wheat, Triticum aestivum (2n=6x=42, AABBDD). To expedite transfer of TTKSK resistance from Ae. tauschii, a direct hybridization approach was undertaken that integrates gene transfer, mapping, and introgression into one process. Direct crossing of Ae. tauschii accessions with an elite wheat breeding line combines the steps of gene transfer and introgression while development of mapping populations during gene transfer enables the identification of closely linked markers. Direct crosses were made using TTKSK-resistant Ae. tauschii accessions TA1662 and PI 603225 as a males and a stem rust-susceptible T. aestivum breeding line, KS05HW14, as a female. Embryo rescue enabled recovery of F1 (ABDD) plants that were backcrossed as females to the hexaploid recurrent parent. Stem rust-resistant BC1F1 plants from each Ae. tauschii donor source were used as males to generate BC2F1 mapping populations. Bulked segregant analysis of BC2F1 genotypes was performed using 70 SSR loci distributed across the D genome. Using this approach, stem rust resistance genes from both accessions were located on chromosome arm 1DS and mapped using SSR and EST-STS markers. An allelism test indicated the stem rust resistance gene transferred from PI 603225 is Sr33. Race-specificity suggests the stem rust resistance gene transferred from TA1662 is unique and this gene has been temporarily designated SrTA1662. Stem rust resistance genes derived from TA1662 and PI 603225 have been made available with selectable molecular markers in genetic backgrounds suitable for stem rust resistance breeding.