Location: Hard Winter Wheat Genetics Research2015 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:
Objective 1. More than 13,000 wheat breeding samples from 10 breeding programs were analyzed for molecular markers in the USDA-ARS Central Small Grains Genotyping Laboratory. The SRPN, NRPN, and RGON regional wheat nurseries were also characterized with more than 60 gene-specific markers linked to important traits of interest to breeders. A total of over 130,000 gene-specific marker data points were generated in 2015. In addition, over 50,000,000 genome-wide GBS marker data points were generated for wheat and barley genetics programs for the Triticeae Coordinated Agricultural Project. The data were used by wheat and barley researchers for characterizing and selecting breeding lines with desired combinations of agronomic and pest resistance traits. More than 5,000 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 with good resistance. In some cases, resistant lines were selected and then shipped back to the breeders for further evaluation. More than 3500 wheat lines from wheat breeders and geneticists in the Great Plains region were screened for resistance to stripe rust at Rossville, KS. The test also included the SRPN, NRPN, and RGON regional nurseries and four mapping populations for resistance to stripe rust. This was the fifth 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 resistance genes Sr22, Sr26, Sr35, and Lr34 in combination. Objective 2. Genotyping-by-sequencing (GBS), a new high-density genetic marker technology, was used to map and identify markers for different traits including resistance to wheat Fusarium head blight, leaf rust, stem rust, stripe rust, pre-harvest sprouting, and Hessian fly. GBS markers for key traits are being converted into KASP markers, a user-friendly marker system, for marker-assisted selection. Twenty-seven GBMAS (genotyping by multiple amplicon sequencing) markers were developed for 10 important agronomic and pest resistance traits in wheat. The new markers were validated by comparison of results with traditional markers for each trait. GBMAS has relatively simple protocols, fast turnaround times, high reliability, and low costs. An irrigated stem rust field screening nursery was conducted in 2014/2015. 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. 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; 3) heat stress tolerance, and 4) adult plant leaf rust and stripe rust on a diverse panel of 305 hard winter wheat lines from the Great Plains. Objective 3. 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 correlated with differences in the protein-coding sequences. The goal is to determine which genes in the pathogen explain the differences in virulence patterns. We have identified two leaf rust proteins that appear to be recognized by wheat resistance genes Lr9 and Lr26. We will now be able to study how the plant recognizes the proteins as well as what amino acid changes are responsible for changes in virulence. Hessian fly is a destructive pest of wheat and a model organism to study gall midges. Hessian fly has six developmental stages including eggs, three instars of larvae, pupae and adults. The molecular mechanisms controlling the transition between different stages are not known and could provide useful information to develop new means to control this destructive pest. We have used the recently developed technology called RNA-Seq to have systematically analyzed genes that are differentially expressed between two successive stages of Hessian fly. We found that there was a massive shift in gene expression when the insect transitioned from one stage to the next, and each stage expressed a unique combination of genes. The large data sets of differentially expressed genes identified in this study should be very useful to provide targets for further research that could eventually lead to new means to control this insect pest. The information reported in this study should also be very useful for comparative research for other insect species as well as for non-insect organisms. Hessian fly is a destructive pest of wheat and can overcome wheat resistance relatively quickly (within 3-8 years after the initial deployment of a resistance gene). To develop wheat cultivars with more durable resistance, we need a better understanding of the molecular mechanisms for Hessian fly avirulence or virulence. The first step to reveal the mechanism for Hessian fly avirulence/virulence is to map and clone Hessian fly avirulence/virulence genes. To map and clone Hessian fly avirulence genes, we need to identify useful molecular markers. During this year, we identified over 7,000 single nucleotide polymorphisms (SNPs) from three different Hessian fly populations. These observations indicate that the identified SNPs could be converted into genetic markers for mapping Hessian fly avirulence and other interesting traits.
Shen, X., Ma, L., Zhong, S., Liu, N., Zhang, M., Chen, W., Zhou, Y., Li, H., Zhang, Z., Li, X., Bai, G., Zhang, H., Tan, F., Ren, Z., Luo, P. 2015. Identification and genetic mapping of the putative Thinopyrum intermedium-derived dominant powdery mildew resistance gene PmL962 on wheat chromosome arm 2BS. Theoretical and Applied Genetics. doi: 10.1007/s00122-014-2449-x.