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United States Department of Agriculture

Agricultural Research Service

Research Project: Wheat Stem Rust Cooperative Research - Oklahoma 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:

Immediately following our first statewide replicated yield trial with Ug99-resistant materials in 2012, we followed that up in 2013 with a reduced slate of experimental lines (and related reselections) in more locations and with more variety-development program (VDP) assays generally targeted at end-use quality and disease resistance. The original set of lines featured alien resistance genes Sr22, Sr35, Sr39, Sr40 introgressed singly into adapted backgrounds (courtesy of USDA-ARS, Manhattan, KS). Briefly, we are now pursuing two tracks: i) reselections of OK11876 (Fuller*2//RL6088/2174*2) which was previously confirmed to carry Sr40 but surprisingly rated as moderately susceptible to Ug99 and other races present in the field at Kenya, and ii) further testing of the elite line OK11823 (Duster*2//Mq(2)5*G2919-k/2174) which, oddly, was not confirmed to carry Sr35 as intended but was rated as moderately resistant in Kenya. Both lines performed in the top-LSD group for grain yield and offer moderate to full levels of resistance to wheat soilborne mosaic and wheat spindle streak mosaic and moderate resistance to tan spot. OK11867 appears to harbor effective resistance to multiple isolates of stripe rust under field infection in Kansas. These and other selections from 2013 will provide focal points for future crossing with the objective to further generate 2- and 3-gene combinations for stem rust resistance. We wish to make this germplasm, and others related to them forthcoming, available to those collaborating on this project as a next-generation Great Plains platform for introgression of multiple resistance genes.

Three crossing blocks were established in 2012-2013 to further introgress Ug99 resistance from divergent and multiple donors. About 30 single, three-way, and double crosses were completed using the adapted donors mentioned above, plus Kingbird, KSWGGRC52, and new sources of resistance featuring Sr26 and Sr39. Our primary emphasis in the past two years was to hybridize confirmed 2-gene combinations with adapted recipient lines showing field resistance (source unknown) to Ug99 and other races in Kenya. The recipient lines included locally adapted elite inbreds.

Expected accomplishments in the subsequent year: a) We expect to accomplish early-generation bulk testing and selection in segregating populations, including mid-generation headrow populations, developed previously which have the greatest likelihood of producing multi-Sr gene recombinants. In the absence of stem rust pressure in the field, selection will focus on a wide array of traits crucial to adaptation in the southern Plains, including multiple diseases naturally present. b) Hybrid progenies will be produced which feature complex pyramids for resistance to stem rust and likely other rusts. New multi-resistance gene donors will be introduced from USDA-ARS germplasm featuring shorter alien chromosome segments. Of greatest interest are BCF2-derived derivatives of Duster containing three alien Sr genes, plus Lr34, framed in smaller chromosome segments, and new D-genome sources of resistance introgressed from Ae. tauschii. Hybrid progenies will be produced using new and further improved elite experimental lines as recipients.


Last Modified: 9/10/2014
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