Location: Plant Science Research2008 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
Progress relates to National Program 301 Plant Genetic Resources, Genomics and Genetics Improvement, Component 3 Genetic Improvement of Crops, Problems Areas 3B Untyped Diversity and 3C Germplasm Enhancement by identifying and developing new sources of disease resistance. This project replaces Project #6645-22000-015-00D, which terminated on 3/27/2008. About 1,000 wheat breeding lines, representing wheats from states east of the Mississippi River were evaluated for resistance to powdery mildew (Pm genes) and yellow rust (Yr genes), also known as stripe rust. Genetic base for powdery mildew resistance was fairly narrow, with only four effective genes (Pm1a, Pm17, Pm34, and Pm35) present in the germplasm. Resistance to yellow rust was even narrower, with only two effective genes present (Yr9 and Yr17). However, adult-plant resistance to yellow rust was apparent in 25% of lines tested. About 160 F1s and F2s were made between 13 minor gene germplasm lines and wheat progenitors for resistance to powdery mildew, yellow rust, leaf rust and stem rust. Molecular markers from the project are enabling breeders and geneticists to select for disease resistance more rapidly. More than 150,000 marker-assisted selection data points were produced and analyzed during 2008. Thousands of breeding lines have been selected that carry genes conferring resistance to Fusarium head blight, powdery mildew, Barley yellow dwarf virus, leaf, stripe and stem rust. Molecular markers were also used to rapidly deploy genes for resistance to head scab into cultivars adapted to the Southeast by backcrossing. Seed of plants having the scab resistance gene pyramids are being provided to breeders for evaluation in field nurseries during Fall 2008. Lines with acceptable performance will be released as varieties. The eastern United States (U.S.) wheat powdery mildew population was analyzed for virulence frequencies and variation. North-south subdivision was found in the population, consistent with a hypothesis of restricted gene flow. The eastern wheat powdery mildew population compared to populations from the United Kingdom and Israel showed strong homology among three populations, consistent with the hypothesis that wheat powdery mildew was introduced into the U.S. with wheat brought by colonists, rather than infecting wheat through a host-range expansion from a wild grass native to the New World. More genetic diversity was found in samples from northerly and cooler locations, suggesting that the population in less conducive areas is subjected to significant genetic bottlenecking. A protocol to rapidly prepare crown samples for histological examination using a microwave was developed and used to compile over 250 images into a single serial animation that allowed us to identify tiller arrangement as well as four regions of the crown that differ in the kind of damage sustained from freezing stress. Rye, wheat, barley and oats were grown under controlled conditions, frozen at varying temperatures and then analyzed histologically. Comparisons of damage within crown tissues of four species were made. Continued with quantitative trait loci (QTL) analysis of three oat populations.
1. Identification of new sources of adult-plant resistance to wheat stripe rust. Wheat stripe rust has been a major yield-reducing factor in central and eastern parts of the U.S. since 2000. Thirteen wheat breeding lines from ARS and other public breeding programs were analyzed under controlled conditions, and in the field at 6 locations in the U.S. Resistance to stripe rust was found and confirmed to be highly effective. These germplasms will enable researchers to develop and release wheat varieties that have resistance to stripe rust. This accomplishment relates to National Program 301 Plant Genetic Resources, Genomics, and Genetics Improvement, Research Component 3 Genetic Improvement of Crops, Problem Statement 3C Germplasm Enhancement.
2. Development and release of stem rust resistant specialty wheats. 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. Two hard red lines (ARS03-3805 and ARS03-4736) and two hard white lines (ARS04-1249 and ARS05-1034) were developed for production in North Carolina. In addition to high protein, bread quality flour, these lines also have resistance to the Ug99 race of wheat stem rust. These lines will serve as the basis for new markets for wheat producers in North Carolina. This accomplishment relates to National Program 301 Plant Genetic Resources, Genomics, and Genetics Improvement, Research Component 3 Genetic Improvement of Crops, Problem Statement 3C Germplasm Enhancement.
3. Mapping a new source of resistance to powdery mildew resistance in wheat. Powdery mildew causes yield losses in wheat in the eastern U.S. Molecular markers were identified that are linked to a new resistance gene designated Pm37 that provides resistance to all isolates of powdery mildew tested. The new molecular markers are being used to deploy this broadly effective gene into improved wheat varieties having genes pyramids. This work will enable researchers to develop varieties with more durable disease resistance. This accomplishment relates to National Program 301 Plant Genetic Resources, Genomics, and Genetics Improvement, Research Component 3 Genetic Improvement of Crops, Problem Statement 3B Capitalizing on Untyped Genetic Diversity.
4. Identification of new sources of resistance to Septoria tritici blotch (STB) and Stagonospora nodorum blotch (SNB). STB and SNB take 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. Over 250 advanced lines were tested in 2007, and 280 advanced lines were tested in 2008. Among these lines were a majority 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 six regional nurseries. These data will enable researchers to release wheat varieties that have a higher average level of resistance to STB and SNB. This accomplishment relates to National Program 301 Plant Genetic Resources, Genomics, and Genetics Improvement, Research Component 3 Genetic Improvement of Crops, Problem Statement 3C Germplasm Enhancement.
5. New information on mycotoxin accumulation in wheat. Current Fusarium head blight (FHB) forecasting models and resistance breeding programs are based on weather during a 22-day period approximately centered on mid-flowering in wheat. However, an investigation of the 2003 FHB epidemic in the Southeastern U.S. suggested that weather later in the grain-fill period had a greater impact on disease and mycotoxin development. For the first time, it has been demonstrated that increasing numbers of moist days in the post-flowering period are associated with elevated disease and deoxynivalenol (DON) levels. Moreover, extended post-flowering moisture can alter the ranking of cultivars for disease and toxin resistance traits. These findings will help researchers provide accurate forecasts of DON levels, and will help breeders screen for resistance to DON development during wet springs. This accomplishment relates to National Program 301 Plant Genetic Resources, Genomics, and Genetics Improvement, Research Component 3 Genetic Improvement of Crops, Problem Statement 3C Germplasm Enhancement.
6. Genetic location of genes for winter hardiness in oat. Seven quantitative trait loci (QTL) and four complementary epistatic interactions were identified that accounted for 56% of the phenotypic variation for oat crown freezing tolerance in a Kanota x Ogle recombinant inbred line population. All loci where Kanota alleles increased crown freezing tolerance showed complementary epistasis for decreased crown freezing tolerance with the QTL near UMN13. Two of the major QTL identified were in the linkage groups associated with a reciprocal translocation between chromosomes 7C and 17. These findings aid in breeding oats for improved winter hardiness. This accomplishment relates to National Program 301 Plant Genetic Resources, Genomics, and Genetics Improvement, Research Component 3 Genetic Improvement of Crops, Problem Statement 3B Capitalizing on Untyped Genetic Diversity.
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 in North Carolina to produce high quality flour for on-farm or small bakery, local use.
Miranda, L.M., Peruginia, L., Srnic, G., Brown Guedira, G.L., Marshall, D.S., Leath, S., Murphy, J.P. 2007. Genetic Mapping of a Triticum monococcum-derived Powdery Mildew Resistance Gene in Common Wheat. Crop Science. 47:2323-2329.