Location: Plant Science Research2010 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
Approximately 3,500 wheat, barley, and oat varieties and breeding lines were evaluated for resistance to powdery mildew, and rust diseases. Powdery mildew resistance in wheats adapted to the eastern U.S. seem to be based on different combinations of Pm genes, with one of the major contributors being Pm1a. Powdery mildew isolates were identified that could distinguish putatively new resistance genes from previously named genes. Suppression of Pm8 by the Pm3a gene common in eastern U.S. wheat varieties was demonstrated. DNA markers were used to screen regional germplasm for Pm8 and the Pm3a. 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. 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. 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 evaluated. Reaction to Stagonospora nodorum blotch was evaluated in 270 elite wheat lines. A new technique for imaging freeze-damage within plants was developed and is in routine use. Existence of a spherical barrier in the crown tissue of oat that appears to prevent the spread of freeze damage into critical meristematic regions was demonstrated. A metabolomic study that may indicate the composition of the barrier was completed and is being analyzed and correlated with a quantitative assessment of the barrier intensity.
1. New wheat germplasm for resistance to stem rust race Ug99. Stem rust race Ug99 is a globally-important pathogen, capable of widespread crop losses. ARS researchers at Raleigh, NC developed 750 wheat lines having stem rust genes combined in two, three, four, and five gene stacks (or pyramids). These lines also have gene combinations for leaf and yellow rusts. These lines will greatly aid U.S. and international wheat breeders develop better worldwide resistance to stem rust race Ug99.
2. 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 ‘NuEast’ and the hard white winter wheat ‘Appalachian White’ were released to seedsmen and farmers in NC, VA, KY, and GA by ARS researchers at Raleigh, NC. 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 North Carolina Organic Bread Flour Project.
3. 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 4,000 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.
4. New sources of resistance distributed to wheat breeders worldwide. Stem rust race Ug99 is a globally-important pathogen, capable of widespread crop losses. ARS researchers at Raleigh, NC developed and distributed 30 advanced lines of wheat having multiple-gene resistance to stem rust race Ug99 to wheat breeders in 32 countries in cooperation with the International Wheat and Maize Improvement Center in Mexico. These 30 lines will serve as sources of resistance to Ug99 in wheat varieties throughout the world, thereby reducing the losses caused by this disease and increasing global food security.
5. Development of 3D imaging process that allows visualization of internal organs of plant and animal tissue. ARS researchers at Raleigh, NC developed a new imaging technique that is in routine use to study freeze-damage within plants. This technique was used to demonstrate the existence of a spherical barrier in the crown tissue of oat that appears to prevent the spread of freeze damage into critical meristematic regions. The new imaging technique has considerable versatility and it is being used to study tumors in mammalian livers as well as fungal infection in immature corn seeds.
6. Facilitating release of novel wheat powdery mildew resistance. Wheat powdery mildew remains one of the most widely distributed wheat diseases in the world, and can cause serious losses in mild, humid environments. ARS researchers at Raleigh, NC organized and evaluated screening of 150 wheat lines from the eastern U.S. for wheat powdery mildew resistance. The screening enabled breeders to know which genes are present in new varieties to be released and which ones had novel resistance genes. Powdery mildew screening research also helped confirm the suspicion that in certain combinations, one powdery mildew resistance gene inhibits the resistance provided by another.
7. Improving resistance to Stagonospora nodorum blotch (SNB) in soft red winter wheat. SNB takes a variable but chronic toll on wheat yield and test weight in the eastern U.S., and breeding programs have lacked the capacity to screen for resistance. ARS researchers in Raleigh, NC screened over 270 advanced wheat lines for SNB resistance, including a significant share of the soft red winter wheat varieties to be released in the next two years. Data on cultivar resistance level were supplied to 25 breeders in 15 states and coordinators of 6 regional nurseries. The 50 most SNB-resistant lines were provided to collaborators for additional screening and crossing. This evaluation helps researchers release wheat varieties with a higher level of resistance to SNB.
8. Identifying the key-time for deoxynivalenol (DON) development in Fusarium-infected wheat. Fusarium head blight (FHB) has reached damaging levels in the eastern soft red winter wheat area in each of the last three years. ARS researchers in Raleigh, NC, have shown that post-flowering moisture increases both scab and production of the deoxynivalenol (DON) toxin, which even in small quantities renders grain unfit for human or animal consumption. Their research has pinpointed the main time period for FHB infections in southeastern U.S. conditions and also identified the scenario that likely gives rise to sound-appearing grain with excessive DON content. Understanding disease development from wheat flowering to harvest allows us to more accurately forecast DON risk and manage high-DON situations.
9. Development of SNP markers for high-throughput genotyping. Single nucleotide polymorphisms (SNPs) are the DNA marker of choice due to availability of cost- and labor-effective automated genotyping systems. ARS researchers at Raleigh, NC developed SNP –based assays for genes in wheat, including the major loci for plant height and photoperiod response as well as genes conferring resistance to the cereal rust and Fusarium head blight pathogens. The presence of these important genes in U.S. wheat cultivars and in thousands of accessions in the USDA-ARS National Small Grains Collection can now be easily assessed. These SNP markers will greatly aid U.S. and international wheat breeders more rapidly develop improved varieties.
5. Significant Activities that Support Special Target Populations
The development of wheat varieties having high protein, bread wheat end-use quality will enable small, niche farmers (less than 100 acres/farm and under $250,000 annual gross receipts) in North Carolina to produce high quality flour for on-farm or small bakery, local use.