Location: Hard Winter Wheat Genetics Research2014 Annual Report
1a. Objectives (from AD-416):
Objective 1: Identify and develop adapted hard winter wheat germplasm with improved resistance to leaf rust, stripe rust, stem rust, Hessian fly, Fusarium head blight, and with tolerance to heat and drought stress. Sub-objective 1.A: Develop germplasm with resistance to leaf rust, yellow rust, and stem rust. Sub-objective 1.B: Develop germplasm with resistance to Hessian fly. Sub-objective 1.C: Develop germplasm with resistance to Fusarium head blight. Sub-objective 1.D: Develop germplasm with tolerance to post-anthesis heat stress. Sub-objective 1.E: Develop germplasm with tolerance to drought stress. Sub-objective 1.F: Conduct cooperative development of hard winter wheat cultivars. Objective 2: Develop more efficient wheat breeding techniques based on high-throughput phenotyping and genotyping methods as well as genomic selection models. Sub-objective 2.A: Develop new high-throughput phenotyping platform for rapid assessment of agronomic and physiological traits in field trials. Sub-objective 2.B: Identify high-throughput markers for important traits. Sub-objective 2.C: Conduct collaborative development of genomic selection models for prediction of yield, agronomic traits, and grain quality and evaluate prediction accuracy. Objective 3: Increase knowledge of the molecular basis for virulence and resistance for leaf rust and Hessian fly, and tolerance to heat stress in wheat. Sub-objective 3.A: Identify mechanisms of virulence and resistance for leaf rust. Sub-objective 3.B: Identify mechanisms of virulence and resistance for Hessian fly. Sub-objective 3.C: Identify mechanisms of tolerance for heat stress.
1b. Approach (from AD-416):
Production of hard winter wheat is limited by recurring intractable problems such as diseases, insects, heat stress, and drought stress. In addition, emerging problems, such as Ug99 stem rust, threaten the sustainability of production. The first objective of this project is to identify and develop adapted hard winter wheat germplasm with improved resistance to leaf rust, yellow rust, stem rust, Hessian fly, Fusarium head blight, and tolerance to heat and drought stress. We will identify sources of resistance, transfer the resistance genes into adapted backgrounds, identify linked markers, validate the gene effects, and release new germplasm lines for cultivar development. The second objective is to develop more efficient wheat breeding techniques based on high throughput phenotyping and genotyping methods as well as genomic selection models. High-throughput phenotyping platforms will be developed using proximal sensing and georeferenced data collection for rapid assessment of field plots. Genotyping-by-sequencing will be used to characterize genome-wide molecular markers on breeding material and apply genomic selection in wheat breeding. New high-throughput markers will be developed for marker-assisted selection of traits of interest. The third objective is to increase our knowledge of the molecular basis for virulence/avirulence and resistance for leaf rust and Hessian fly, and tolerance to heat stress in wheat. Greater understanding of avirulence effectors in the Hessian fly and the leaf rust pathogen may lead to better strategies for durable resistance. Likewise, uncovering the mechanisms of abiotic stress tolerance may lead to discovery of new tolerance genes with improved or complementary effects.
3. Progress Report:
1. More than 11,000 wheat breeding samples from 10 breeding programs were analyzed for molecular markers in the USDA-ARS Central Small Grains Genotyping Laboratory. We also analyzed three regional wheat nurseries with more than 50 specific markers linked to important traits of interest to breeders. A total of over 100,000 allele-specific marker data points were generated in 2014. The data were used by wheat researchers for selecting wheat breeding lines. 2. Genotyping-by-sequencing (GBS), a new high density marker technology, was done for 10 recombinant inbred populations or doubled haploid populations to map resistance in wheat to Hessian fly, soilborne wheat mosaic virus, wheat streak mosaic virus, Fusarium head blight, and other traits. Data are being analyzed to map the genetic loci controlling these traits. 3. We are working to develop methods for GBMAS (genotyping by multiple amplicon sequencing). GBMAS first amplifies up to a few hundred predefined marker targets in a multiplex PCR reaction. Then unique barcodes are ligated to the PCR products for each individual. Samples are then pooled and prepared for high throughput sequencing. Barcodes are used to separate resulting sequence reads and make genotyping calls. This platform has relatively simple execution, fast turnaround times, high reliability, and low costs. 4. More than 3,500 wheat lines from wheat breeders and geneticists in the Great Plains region were screened in the greenhouse for resistance to the Hessian fly. Results were sent to breeders to aid in the selection of elite lines. In some cases, resistant lines were selected, dug up, and were shipped back to the breeders. 5. An irrigated stripe rust screening nursery at Rossville, KS was planted with more than 1500 breeder advanced lines. The nursery also included four mapping populations for resistance to stripe rust. Unfortunately, the nursery was lost due to winterkill due to late planting. 6. An irrigated stem rust field screening nursery was conducted in 2013/2014. Two mapping populations for minor gene resistance to stem rust were scored for resistance reactions. These data will be used in the coming year to map the locations of the resistance genes. In addition, selections were made in segregating populations for resistant germplasm development. 7. This was the fourth year of work under specific cooperative agreements with six public wheat breeding programs to introgress resistance to Ug99 stem rust into elite adapted wheat cultivars. Each breeding program made crosses between resistant donor lines and their own elite breeding lines. The primary goal is to produce new varieties with three-gene or four-gene combinations of resistance genes Sr22, Sr26, Sr35, and Lr34. 8. Association mapping studies are in various stages of completion for: 1) adult plant leaf rust on a core collection of 1414 diverse winter wheat lines from the National Small Grains Collection in Aberdeen, ID; 2) adult plant stem rust, leaf rust, and stripe rust on a panel of 205 hard and soft winter wheat entries from elite nurseries; and 3) heat stress tolerance, and adult plant leaf rust and stripe rust on a diverse panel of 305 hard winter wheat lines from the Great Plains. 9. In collaboration with other researchers, the genomes of one hundred and thirty-four isolates of the leaf rust fungus have been sequenced. Specific virulence of these isolates to different resistance genes is being used to identify differences in the protein-coding sequences that might explain the differences in virulence patterns. To date, 11 candidate genes have been identified by comparative genomics that might mediate the resistance response in the plant. 10. Studies are ongoing on developing synoptic models of resistance gene durability. A model was developed for predicting the occurrence of new virulent races for combinations of resistance genes based on the exponential failure distribution. This model accounts for rates of mutation, sexual recombination, migration, pathogen population size, and the number of genes in the combination. A second synoptic model for predicting plant disease resistance gene durability singly and in combinations has been developed based on the balance of effectiveness of resistance and fitness costs. Together, these synoptic models will be useful for developing improved strategies for resistance gene stewardship. A manuscript is in preparation.
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