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United States Department of Agriculture

Agricultural Research Service


Location: Plant Science Research

2011 Annual Report

1a. Objectives (from AD-416)
Objective 1: Identify sources of resistance to foliar fungal pathogens and introgress resistance into adapted wheat. Objective 2: Develop improved methods of marker-assisted selection and apply markers in development of improved wheat and oat. Objective 3: Characterize frequencies of virulence in pathogen populations to resistance sources in wheat germplasm and evaluate the risk potential of virulence transfer through gene flow. Objective 4: Characterize genetic factors conferring winter-hardiness in oat.

1b. Approach (from AD-416)
Approach 1: Evaluation, identification, and incorporation of major gene resistance in wheat to powdery mildew and stripe rust using greenhouse, growth chamber and field facilities. Evaluation and identification of major gene resistance in progenitors of wheat to powdery mildew and stripe rust. Evaluation, identification, and incorporation of minor gene resistance in wheat to powdery mildew and stripe rust. Approach 2: Will apply marker-assisted selection to determine if we can rapidly introgress and pyramid new fungal resistance genes into soft winter wheat germplasm. Will apply marker technology to characterize the genetic factors for resistance by haplotyping, genetic linkage and QTL analyses. Phenotypic and marker analyses will be used to identify and develop germplasm having genes of interest for use in developing improved cultivars of small grains. Approach 3: Powdery mildew samples are obtained from collaborators in the U.S., U.K., and Middle East. Virulence frequencies are determined using powdery mildew resistance gene differentials on detached-leaf plates. In order to evaluate the extent of population subdivision, migration, and gene flow, nested cladistic analysis will be used because it may allow inferences about historical processes such as fragmentation and range expansion. Approach 4: Two oat cultivars differing in winter-hardiness that have been grown in the UOWHN for more than 40 years have been used to develop a mapping population for identification of genomic regions containing winter-hardiness genes. After cold acclimation, crowns will be prepared for freezing by trimming roots and leaves to approximately 3 cm. To identify markers suitable for high-throughput genotyping for this QTL and to identify new regions associated with winter-hardiness, SSR markers will be evaluated on the mapping population.

3. Progress Report
Adult-plant resistance to stripe rust has a major effect in protecting the eastern U.S. wheat crop, as most seedlings Yr genes have been defeated. Approximately 1100 F1s were made between all possible combinations of 8 minor gene germplasm lines for resistance to powdery mildew, yellow rust, leaf rust and stem rust. Segregating populations between wheat progenitor-based stem rust resistance and adapted wheat genotypes were screened for adult-plant resistance. Single nucleotide polymorphisms (SNP) markers for detection of the durable Lr34/Yr18 genes were developed and used to evaluate local cultivars and diverse germplasm from the National Small Grains Collection. Approximately 30,000 samples of wheat and oat were genotyped with deoxyribonucleic acid (DNA) markers, including newly developed single nucleotide polymorphism markers for each species. Analyzed markers were associated with more than 50 genes for resistance to disease and insect pests, end-use quality and adaptation. Wheat lines were identified having combination of genes for resistance to leaf and stem rust, powdery mildew, and Fusarium head blight. New markers were developed for high-throughput identification of genes for resistance to Wheat Soil-borne Mosiac Virus and durable wheat stem rust resistance gene Sr2. These new markers are being used to evaluated local cultivars and breeding lines, as well diverse germplasm from around the globe. Experiments were conducted to more precisely define the time period of greatest wheat susceptibility to Fusarium head blight infection and to determine the effects of different harvest timings on deoxynivalenol levels in wheat grain. The effects of moderately resistant cultivars and fungicides in managing wheat and barley head scab were demonstrated in multiple location experiments. DNA marker analyses and selection of entries in field experiments were done to assess the effectiveness of different genes conferring resistance to Fusarium head blight. Experiments were conducted to relate different levels of Stagonospora nodorum blotch severity to yield and test weight in wheat. Differences in host-selective toxin production among southeastern U.S. Stagonospora nodorum isolates and differences in toxin sensitivity in the southeastern U.S. wheat germplasm were identified. Reaction to Stagonospora nodorum blotch was evaluated in 270 elite wheat lines. Metabolomic analysis indicated a significant shift in numerous metabolic pathways as a result of freezing. Evaluation of The Oat Winter Hardiness Nursery for simple sequence repeat (SSR) markers after 3 years indicates a strong relationship between markers and field survival. Controlled freeze testing of the Uniform Southern Soft Red Winter Wheat Nursery is continuing for the second year.

4. Accomplishments
1. Genes for scab resistance in winter wheat identified. High yielding wheat varieties with resistance to wheat scab are needed to prevent losses of grain yield and quality. ARS researchers at Raleigh, NC, associated deoxyribonucleic acid (DNA) markers with scab resistance in a set of 250 winter wheat breeding lines. Their research validated the presence of previously mapped scab resistance genes in these adapted wheat lines and identified new genes contributing to resistance. This result will aid the application of marker-assisted breeding to develop high yielding, scab resistant wheat varieties.

2. New deoxyribonucleic acid (DNA) markers for small grains developed. ARS researchers at Raleigh, NC, collaborated with other ARS scientist and university researchers to identify more than 10,000 new markers based on differences in DNA sequences among wheat and oat varieties from around the world. Thousands of these new markers can be evaluated in a single assay, which greatly increases the efficiency with which researchers can locate and select for important genes in these crops. In addition, the cost effectiveness of the new marker assays will allow breeders to more efficiently use improved techniques in marker-assisted breeding to select new varieties of wheat and oats.

3. New wheat germplasm for resistance to stem rust race Ug99 distributed. Stem rust race UG99 is capable of causing widespread, global crop losses. ARS researchers in Raleigh, NC, developed 328 winter wheat lines having stem rust genes combined in two, three, and four gene stacks. These same wheat lines also have two and three gene combinations for resistance to yellow (stripe) rust and leaf rust. This germplasm was distributed to winter wheat researchers in the U.S. and globally through CIMMYT-ICARDA-Turkey. These wheats will greatly aid wheat breeders throughout the world to develop rust resistant varieties.

4. Evaluation of U.S. wheat and barley in Kenya to Ug99 stem rust. Stem rust race Ug99 is a globally-important pathogen, capable of widespread crop losses. ARS researchers at Raleigh, NC, organized and evaluated 4,320 wheat and barley varieties and germplasm lines in Njoro, Kenya for resistance to Ug99 stem rust. This information will enable breeders in the U.S. to identify and release wheat and barley varieties having Ug99 resistance. This will result in the U.S. being able to deploy resistance to Ug99 stem rust in advance of the pathogen arriving in the U.S.

5. Development and release of specialty wheats for the eastern U.S. Wheat varieties having bread wheat, end-use quality are needed for production in the eastern U.S. in order to serve as a local source of high protein flour for organic and artisan bakers. The hard red winter wheat lines ARS05-0241 and ARS07-0785 will be named and released to seedsmen in August 2011. These two new varieties follow the 2009 release of the hard red winter wheat ‘NuEast’ and the hard white winter wheat ‘Appalachian White’. These wheat varieties were critical in the formation of an eight-bakery cooperative formed in Asheville, NC having the goal of locally-produced wheat, flour, and bread products. These wheat varieties also provided the thrust behind the formation of the non-profit organizations North Carolina Organic Bread Flour Project and Carolina Ground.

6. New molecular tools for combatting wheat powdery mildew. In the mid-Atlantic U.S. and other wheat-growing regions of the world, powdery mildew is a major disease that results in significant yield losses. Basic features of the pathogen population remain a mystery, including the migratory potential of new strains that can overcome previously effective resistance genes in wheat. A set of new deoxyribonucleic acid (DNA) microsatellite markers were developed that will allow us to answer questions such as whether new virulent strains that appear in one part of the U.S. are likely to migrate to other regions, overcoming previously resistant genes there as well.

7. New understanding of why wild resistance genes sometimes fail. When disease resistance genes from wild wheat relatives are introduced into cultivated wheat, the genes sometimes have reduced or no effect in their new background. It was discovered that the resistance to powdery mildew conferred by the gene Pm8 was suppressed in some wheat cultivars. A gene linked to the suppressive effect was identified near two storage protein genes, Gli-A1 and Glu-A3. These genes are in turn closely linked to another powdery mildew resistance gene, Pm3. The discovery will help breeders avoid combining genes that nullify each other’s effects.

8. New markers for oat winter hardiness identified. Of the winter cereal crops, winter oats are most susceptible to freeze damage. Combining data on freeze damage of an oat population in controlled environment chambers with information from seventy newly developed deoxyribonucleic acid (DNA) markers allowed ARS scientist at Raleigh, NC, to identify markers accounting for multiple winter hardiness component traits. The addition of these markers to the genetic map of oat will enhance marker assisted selection for winter hardiness.

Review Publications
Griffey, C., Brooks, W., Vaughn, M., Thomason, W., Paling, J., Pitman, R., Dunaway, D., Corbin, R., Kenner, J., Hokanson, E., Behl, H., Beahm, B., Liu, S., Gundrum, P., Brann, D., Whitt, D., Custis, J., Starner, D., Gulick, S., Ashburn, S., Jones, N., Marshall, D.S., Fountain, M.O., Tuong, T.D., Premakumar, R., Livingston, D.P., Hicks, K.B., Kurantz, M.J., Taylor, F., Moreau, R.A. 2011. Registration of 'Dan' winter hulless barley. Journal of Plant Registrations. 5:1-4.

Kang, J., Clark, A., Vansanford, D., Griffey, C., Brown Guedira, G.L., Dong, Y., Murphy, J.P., Costa, J. 2011. Exotic Scab Resistance Quantitative Trait Loci (QTL) Effects on Soft Red Winter Wheat. Crop Science. 51:924-933.

Mago, R., Brown Guedira, G.L., Dreisigacker, S., Breen, J., Jin, Y., Singh, R., Appels, R., Lagudah, E., Ellis, J., Spielmeyer, W. 2010. An accurate DNA marker assay for stem rust resistance gene Sr2 in wheat. Theoretical and Applied Genetics. 122:735-744.

Kuraparthy, V., Sood, S., Brown Guedira, G.L., Gill, B.S. 2011. Development of a PCR assay and marker-assisted transfer of leaf rust resistance gene Lr58 into adapted winter wheats. Euphytica. 180:227-234.

Last Modified: 06/24/2017
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