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United States Department of Agriculture

Agricultural Research Service

Research Project: Wheat Stem Rust Cooperative Research - Texas A&m University - College Station

Location: Hard Winter Wheat Genetics Research Unit

2012 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:

Our objective is adapted lines for South, Central, and Northeast Texas that combine pyramided genes for Ug99 stem rust resistance with high yield potential, superior quality and resistance to other biotic and abiotic stresses prevalent in Texas. We made one-way, two-way, and four-way crosses designed to combine Ug99 resistance genes into adapted Texas wheat backgrounds. A total of 225 cross combinations to incorporate resistance to Ug99 based on genes Sr2, Sr24, Sr1A.1R, Sr25, Sr22, Sr36, Sr32, Sr35, Sr39, and Sr40 was made in fall of 2011. A total of 201 four-way crosses were made in spring 2012 to combine as many favorable genes as possible.

Plant tissue from these lines will be harvested in November 2012 and sent Manhattan, KS for marker screening. Best combinations will be advanced in the breeding pipeline using doubled-haploid and conventional breeding methods.

Last Modified: 4/2/2015
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