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United States Department of Agriculture

Agricultural Research Service

Research Project: Wheat Stem Rust Cooperative Research - Colorado State University

Location: Hard Winter Wheat Genetics Research Unit

2013 Annual Report


1a.Objectives (from AD-416):
Develop elite hard winter wheat genotypes that incorporate multiple resistance genes that are effective against new African races of wheat stem rust.


1b.Approach (from AD-416):
Bread wheat germplasm lines with effective major gene and/or minor gene resistance against new African races of stem rust are being developed by USDA-ARS as well as many other institutions. These resistance donors will be crossed with multiple local elite breeding lines with high yield potential, grain quality, and tolerance to biotic and abiotic stresses. Good stewardship of valuable new resistance genes requires that they not be exposed singly in commercial cultivars. Endemic stem rust resistance genes, such as Sr24, Sr36, or Sr1A.1R, while very useful against most races, are not effective against all African races, and are not sufficient protection for new resistance genes. Therefore, the goal is to combine two or more new major genes into elite backgrounds. Minor gene or adult plant resistance genes are recommended as a supplement to major gene resistance. Minor genes are expected to be much more durable and do not require special stewardship protocols.

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.


3.Progress Report:

Head selections were made from two crosses that involved different sources of Ug99 resistance and were advanced for line selection in 2014. These sources include a recombined Sr26 source from Australia and a recombined Sr39 source obtained from North Dakota. In 2014 these populations will be subject to selection and advanced for yield trials in 2015.

Twenty-five topcross-derived line selections carrying different sources of Ug99 resistance were made and advanced to unreplicated bulk trials in 2014. The sources of resistance include the Sr26 and Sr35 sources mentioned above. Many of these crosses were made with the SrTmp-carrying cultivar 'Byrd'.

Single backcross segregating progenies with the CIMMYT line 'Kingbird' and five adapted Colorado wheats were grown in the field as spaced-planted F3 populations in 2013. Individual heads harvested from single plants were bulked and will be planted in a space-planted nursery at Fort Collins in September 2013 for line selection in 2014.

Two cycles of marker-assisted backcrossing were done in the greenhouse (fall 2012, spring 2013) utilizing markers associated with Sr22, Sr25, and Sr35. Twenty populations segregating for two or more (plus SrTmp from Byrd) of these genes will be planted in the field in fall 2013 for population and line selection in subsequent years.

Field selections will be made in 2014 to identify adapted progenies carrying multiple stem rust resistance genes. Desirable progenies will be returned to the crossing program.

The new wheat cultivar 'Byrd', which is resistant to moderately resistant to Ug-99 (likely due to SrTmp), was released to seed producers in fall 2011. Byrd has performed especially well in trials in Colorado and it will likely rise very rapidly to over 25% of the 2014 Colorado wheat crop.


Last Modified: 11/27/2014
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