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United States Department of Agriculture

Agricultural Research Service

Research Project: Genetic Improvement of Small Grains for Biotic and Abiotic Stress Tolerance and Characterization of Pathogen Populations

Location: Plant Science Research

2013 Annual Report


1a.Objectives (from AD-416):
1. Identify and develop improved small grain germplasm with resistance to rusts, powdery mildew, Fusarium head blight, necrotrophic pathogens, and freeze tolerance. 1a: Develop wheat germplasm with resistance to stripe rust, leaf rust, stem rust, and powdery mildew. 1b: Develop wheat germplasm with resistance to Fusarium head blight (FHB). 1c: Develop wheat germplasm with resistance to Stagonospora nodorum blight (SNB). 1d: Identify oat, wheat and barley germplasm with tolerance to freezing.

2. Develop improved methods of marker-assisted selection, and apply markers in development of small grains cultivars. 2a: Identify new markers for important traits in eastern winter wheat germplasm. 2b: Evaluate important traits in eastern winter wheat using molecular markers. 2c: Develop new eastern winter wheat germplasm using marker-assisted breeding.

3. Develop new wheat germplasm and cultivars having enhanced end-use characteristics for the eastern U.S.

4. Determine the virulence structure of small grain pathogen populations and evaluate the risk potential of virulence transfer through gene flow. 4a: Determine the virulence frequencies in the wheat powdery mildew pathogen, Blumeria graminis f. sp. tritici, from different regions in the U.S.


1b.Approach (from AD-416):
1. Develop wheat germplasm with resistance to stripe rust, leaf rust, stem rust, and powdery mildew. Develop wheat germplasm with resistance to Fusarium head blight (FHB). Develop wheat germplasm with resistance to Stagonospora nodorum blight (SNB). Identify oat, wheat and barley germplasm with tolerance to freezing.

2. Identify new markers for important traits in eastern winter wheat germplasm. Evaluate important traits in eastern winter wheat using molecular markers.

3. Make new crosses, marker-assisted selection for key traits; phenotyping and selection for improved hard wheats lines; introduce resistance to common bunt; grow and select populations under organic and conventional conditions.

4. Obtain infected plant samples from all states; make single-pustuled isolates, and begin phenotyping and genotyping.


3.Progress Report:
Over 600 wheat powdery mildew isolates from east and west of the Appalachians were created from samples sent by collaborators in 10 states. Virulence data were collected and DNA was extracted for genotyping from all isolates. Next-generation sequencing techniques will be used to identify genetic polymorphism. Population subdivision and migration rates will be estimated, enhancing our understanding of gene flow and the potential for movement of novel virulences.

Advanced experimental wheat lines in eastern and southern regional cooperative nurseries were screened under Stagonospora nodorum pressure, and data on resistance provided to breeding programs. Wheat lines exhibiting high levels of S. nodorum susceptibility were evaluated for presence of genes for sensitivity to fungal products that promote disease. The second year of a multi-location field experiment was carried out to gather data for development of a fungicide decision aid for S. nodorum management.

Data were collected to expand our understanding of how long wheat heads remain vulnerable to infection by Fusarium graminearum, cause of head scab. This brings to an end a four-year field experiment that is providing a precise picture of levels of disease and mycotoxin present in wheat that is infected at various time points following mid-flowering, when susceptibility is at its peak. This information is helpful in disease and mycotoxin risk projections, and in fungicide management decisions.

Freeze test were performed on the Uniform Eastern and the Uniform Southern Soft Red Winter Wheat Nurseries. Freeze-tested and performed an SSR marker analysis of the Uniform Oat and Barley Winterhardiness Nurseries. Performed a Spring-Freeze analysis on the North Carolina Official Variety Test for Wheat and Oats. Established a collaborative investigation with The Canadian Wheat Alliance Program on mechanisms of cold acclimation in wheat. Discovered a technique to image ice formation in frozen crown tissue in 3 dimensions. Continued evaluating freezing tolerance under controlled conditions for the soft red winter wheat community.

Produced a full pipeline of hard red and hard white winter wheats, with 1000 crosses/year, 30,000 head rows/year, and 40-70 new elite experimental lines/year. The emphasis is to select lines having superior bread-baking quality. We have focused on Regional testing in North Carolina, Georgia, Louisiana, Kentucky, Virginia, Ohio, and Maryland. We have expanded International testing to Kenya, Turkey, Turkmenistan, Kazakhstan, Pakistan, New Zealand. All early generation lines are genotyped for quality, disease resistance, insect resistance, dwarfing genes, and vernalization genes.


4.Accomplishments
1. New tools for breeding wheat varieties resistant to Stagonospora nodorum blotch. When unadapted wheat lines are used in crossing for traits such as hardness for bread-making, or disease resistance, sometimes they also donate undesirable traits. This has been the case with several sources of hardness used by breeders to develop bread wheats for the U.S. mid-Atlantic market. Some parent lines have passed on super-susceptibility to Stagonospora nodorum, a fungal pathogen of wheat leaves and heads. Testing with molecular markers and toxins produced in liquid media by strains of this fungus has established that two wheat genes, Tsn1 and Snn3, are often present in the highly susceptible lines. Thanks to this knowledge, screening tools can help breeders avoid the super-susceptible offspring while continuing to utilize desirable traits from the parents.

2. Screening for resistance to soilborne mosaic virus. Wheat yields can be reduced by as much as 30% if plants are infected by wheat soilborne mosaic virus. Host plant resistance is the only effective method of control; no chemical management technique is feasible. Yet field screening of commercial varieties and advanced breeding materials is often hampered by spotty or intermittent virus epidemics. A test was developed to use virus-laden soil in pots to screen wheat seedlings. The procedure gives data in three months, and appears to be accurate and reliable.

3. Screening for tolerance to late spring freeze. Using a more precise test to evaluate spring freeze tolerance in wheat we determined that spring freeze tolerance is under genetic control and it is a trait that is not linked to days-to-heading. This means breeders should be able to transfer the trait to existing cultivars without changing the heading date of the cultivars.

4. New tools for breeding winter wheat adapted to diverse climates. Winter wheat is grown across a vast region and makes up 70% the wheat acreage in the United States. In order to flower normally, all winter wheat varieties require a period of cold referred to as vernalization. By studying a population of lines developed from a cross between winter wheat varieties from North Carolina and Georgia, ARS researchers at Raleigh, NC determined that differences in flowering were associated with the vrn-B1 gene. The vrn-B1 gene was the primary determinant of flowering time at field locations in Georgia and Lousiana and also in North Carolina during 2012 and 2013, when winter temperatures were warm. A newly developed molecular marker has provided a screening tool to help breeders utilize diverse winter wheat germplasm while selecting the appropriate vrn-B1 allele for adaptation to the local environment.

5. 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 germplasm having Ug99 effective resistance genes Sr26, Sr42 and Sr54 in eight different soft winter wheat backgrounds that were distributed wheat breeders in the eastern growing region. The germplasm was developed by backcrossing unadapted spring wheat donor lines to elite breeding lines and varieties from the Eastern United States and selecting for the resistance genes using molecular markers. These new germplasm broaden the diversity of stem rust resistance genes available to eastern winter wheat breeders.


Review Publications
Livingston, D.P., Henson, C.A., Wise, M.L., Tuong, T.D., Tallury, S., Duke, S. 2012. Histological analysis and 3D reconstruction of winter cereal crowns recovering from freezing: a unique response in oat (Avena sativa L.). PLoS One. 8(1): e53468.

Last Modified: 12/21/2014
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