Location: Hard Winter Wheat Genetics Research Unit
2012 Annual Report
In order to produce commercially competitive varieties of the future, new stem rust resistance genes must be incorporated into a forward breeding program. In addition, a backcross breeding program is required both for parent-building and as a hedge if commercially acceptable resistant varieties are needed in the short term. Rapid breeding methods, such as doubled haploids, will be needed to achieve results as quickly as possible.
Phenotypic selection for resistance using common North American races will be difficult in most backgrounds due to the high frequency of endemic stem rust resistance genes. Therefore, marker-assisted selection for new resistance genes will be necessary. Molecular markers are available or under development for virtually all new sources of stem rust resistance. Marker genotypes will be generated locally or in a high throughput facility at the USDA-ARS Regional Small Grains Genotyping Laboratory in Manhattan, KS. Resistance of advanced lines against African races of stem rust will be confirmed by field testing at cooperative research facilities in Kenya or at the USDA-ARS Cereal Disease Laboratory. Testing for agronomic traits, yield, and quality will be performed as usual by the breeding program.
The CSU wheat breeding project is completing the second year of this collaborative project on breeding for resistance to Ug99 stem rust. Marker assays for several stem rust resistance genes were optimized and are in routine use in our breeding program. These include markers for the Sr2, Sr22, Sr25, Sr26, Sr35, and Sr39 resistance genes. Using these markers, we made multiple crosses and backcrosses in both fall 2011 and spring 2012. Multiple populations carrying these genes, derived following marker-assisted backcrossing and forward crossing with products of backcrossing, have moved toward the stage of field selection.
For Sr26, 27 populations were advanced from the last stage of forward crossing in fall 2011 to planting in the field in spring 2012. Individual plant selections were made in summer 2012 and advanced for observation and further selection in 2013. Many of these carry other Ug99 resistance genes, such as SrTmp via Ripper and Byrd, the recombined Sr39 source (WG 3 obtained from Steven Xu in Fargo, ND), and Sr25 (obtained from CIMMYT via Wheatear).
Single backcross segregating progenies with the CIMMYT line 'Kingbird' and five adapted Colorado wheats were grown in the field as spaced-planted populations in 2011. Individual heads were harvested from single plants and were bulked and planted in a space-planted nursery at Fort Collins in September 2011. In 2012, we made single-plant head selections using the "selected bulk" breeding procedure. These populations were planted in September 2012 for another cycle of individual plant selection. A single-seed descent (SSD) derived population between 'Ripper' and 'Bill Brown' was shared with the USDA Lab in St Paul, MN. Using this and other populations, we were able to map the stem rust resistance in 'Ripper' to the same location as other known resistance genes (SrCad and Sr42). We are screening a collection of breeding parents for this marker in collaboration with the genotyping lab at Manhattan, KS. Assuming we have polymorphism for the linked marker, we will use this marker in marker-assisted selection throughout our program. Based on field screening in Kenya, we believe that both 'Ripper' and 'Byrd' carry this resistance. Both of these varieties have been key breeding parents in our program.