Location: Plant Science Research2012 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:
Replicated yield trials were planted in six locations in NC, in addition to replicated trials under organic production conditions in Goldsboro and Kinston. An unusual storm event lodged 15 acres of plot in Raleigh. A late spring freeze rendered mountain locations in Waynesville and Laurel Springs 65% sterile, and uneven field preparation resulted in poor drainage and flooding of the organic trial in Kinston. As a result, we did not harvest four locations of replicated trails. We began to evaluate the response of wheat varieties to changes in levels of ozone and carbon dioxide that are projected to increase in our atmosphere over the next 50 years. Initially, we have identified wheat lines and varieties that respond differently to ozone, carbon dioxide, and increased temperatures. This will enable us to identify the genes involved in greenhouse gas responses, and to breed for resistance. Wheat powdery mildew populations from regions east and west of the Appalachians were genotyped. Population subdivision and migration rates were estimated. Results showed low levels of population subdivision, and suggested that in the U.S., migration of powdery mildew spores takes place from certain regions to certain other regions. 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. Techniques were developed and refined for testing of breeding materials for stem rust resistance, and a large number of wheat lines were screened to help identify both seedling and adult-plant stem rust resistance. More than 30,000 samples from wheat breeding programs were evaluated with markers, resulting in approximately 200,000 marker data points. Regional nurseries were screened with diagnostic markers for genes involved in plant development, disease resistance, and grain quality. 450 eastern wheat lines were genotyped with ~8,600 single nucleotide polymorphism (SNP) markers were grown at three locations in NC and evaluated for resistance to powdery mildew, leaf rust and S. nodorum leaf blotch. Genotypic and phenotypic data are being utilized for association mapping. Genotype calls were made for four mapping populations from crosses between wheat lines evaluated with the wheat high-density SNP array. Genetic linkage maps are being constructed in these populations. Two of the populations were evaluated in the field and greenhouse to map genes related to duration of vernalization requirement, resistance to powdery mildew, leaf rust and S. nodorum. Three uniform nurseries for wheat, two for oat and one for barley were evaluated for freezing tolerance under controlled conditions. One wheat and one oat nursery was evaluated for spring freeze tolerance while in the boot stage. One oat nursery was evaluated for relationship of SSR markers to freezing tolerance.
1. Ug99 stem rust resistant wheat germplam. Stem rust race Ug99 is endemic to East Africa and has spread to the Arabian peninsula. The disease has the potential to attack most of the worlds’ wheat varieties. ARS researchers in Raleigh, NC screened 5,500 lines of wheat in Njoro, Kenya and identified 65 lines that have multiple genes for resistance to Ug99, in 3 and 4-gene combinations. This germplasm was distributed to breeders in 16 countries throughout the world. These lines will greatly aid global breeding efforts to develop stem rust resistant varieties.
2. Millers and bakers in the eastern U.S. need local sources of high protein, bread-quality flour. ARS researchers in Raleigh, NC developed two bread-quality wheat lines having yields equal to the highest yielding soft wheat checks. These two lines were ‘ARS09-367’ and ‘ARS09-724’ These two lines also had excellent test weights (greater than 61 pounds per bushel), good resistance to yellow rust, leaf rust, powdery mildew, and soilborne mosaic virus. They had moderate resistance to scab (Fusarium head blight), Hessian fly, and Septoria. Both were early to moderate maturing. The flour quality of both lines was excellent. These lines will be proposed for release as varieties in 2012-13, and could serve as excellent, local-food commodities for producers and consumers in North Carolina and Virginia.
3. New tools for breeding wheats resistant to Stagonospora nodorum blotch. When unadapted wheat lines are used to introduce desirable traits such as hardness for bread-making, or disease resistance, sometimes they unfortunately also bring along 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 since 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, referred to as Tsn1 and Snn3, are often the culprits 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.
4. New understanding of the progress of Fusarium head blight from flowering to harvest in wheat spikes. Fusarium head blight (FHB) affects whole heads of small-grain plants, yet little is known about how the disease develops following infection at flowering, nor about the concentration or progression of the mycotoxin deoxynivalenol (DON) in chaff and rachis tissues. Fusarium mycotoxin levels in whole small-grain heads are of concern to producers of whole-crop silage, as well as users of straw containing chaff for animal bedding or winter livestock rations. A two-year field experiment showed that during grain-fill, DON concentrations were highest shortly after infection and then declined in grain, while in rachises and glumes, the concentrations increased. Higher mean and maximum DON levels were observed in rachises and glumes than in grain. In a high-FHB year, whole plants destined for forage should be harvested as early as possible after flowering. Straw that may be consumed by livestock could contain significant amounts of DON in chaff, and DON can be minimized if straw is sourced from low-symptom crops. Cultivar FHB resistance ratings and disease data should be useful in predicting whole-head DON levels.
5. New molecular markers for high through-put genotyping of thousands of individuals. ARS researchers in Raleigh developed low-cost, single tube assays that are predictive of the presence of important genes in wheat. These diagnostic markers are based on DNA sequence differences in genes conferring disease resistance, as well as genes for seed color, seed storage proteins, plant height, vernalization and photoperiod requirement. The new markers can be evaluated for as little as five cents per sample, making it cost effective to evaluate thousands of individuals in breeding programs and germplasm collections. The newly developed markers are available to public and private wheat breeding programs interested in using marker-assisted selection for development of elite cultivars with improved quality and disease resistance.
6. Developed a test to evaluate spring-freeze-tolerance in wheat and oat. Spring freezing stress is becoming more of an issue in North Carolina as warmer winters and sudden spring freezes have become more prominent. To date there has been no published report of a test to measure this type of freezing tolerance. Using the newly developed method, we were able to distinguish several spring-freeze-tolerant wheat lines and one spring-freeze-tolerant oat line. Using a similar test we were able to rank the Uniform Southern and Eastern Soft Red Winter Wheat nurseries for freezing tolerance, providing breeders with information about a crucial agronomic trait. The information provided in our spring freeze analysis gives growers the opportunity to include spring freeze tolerance in their list of choices as they decide which cultivars to plant in the fall.
Horevaj, P., Brown Guedira, G.L., Milus, E.A. 2012. Resistance in winter wheat lines to deoxynivalenol applied into florets at flowering stage and tolerance to phytotoxic effects on yield. Plant Pathology. DOI: 10.1111/j.1365-3059.2011.02568.x.