1a. Objectives (from AD-416):
The long-term objective of this project is to provide wheat, barley, and sorghum producers with new pest resistant crops and technologies that will protect their crops from insect pests. Specifically, during the next five years we will focus on the following objectives. Objective 1: Identify new sources of resistance to aphids and other insects in wheat, barley, sorghum, and related species. Subobjective 1A. Evaluate available germplasm resources (national germplasm collections and accessible exotic resources) to identify new sources resistant to insect pests [Russian wheat aphid (RWA), greenbug (GB), and bird cherry-oat aphid (BCOA)] in wheat, barley, sorghum, and related species. Subobjective 1B. Define a visual rating scale for use in greenhouse screening of wheat and barley seedlings for identification of BCOA resistance. Subobjective 1C. Determine the field resistance of barley lines which exhibit a unique visual plant response to RWA feeding as seedlings in the greenhouse which is not clearly assigned to a resistance level by Webster's scale of 1 - 9. Objective 2: Characterize the mechanisms and genetics of new sources of aphid resistance in wheat, barley, and sorghum. Subobjective 2.A. Develop and evaluate genetic populations to determine the genetic control of host resistance to GB, RWA, and BCOA in barley. Subobjective 2.B. Develop and evaluate genetic populations to determine levels of genetic diversity of host resistance to GB, RWA, and BCOA in wheat, barley, and sorghum. Subobjective 2.C. Develop and identify molecular markers to facilitate identification of resistance QTLs and cloning of the resistance gene(s), and to aid selection of breeding lines through marker-assisted selection. Subobjective 2.D. Conduct functional genomics studies on host response to GB attack, leading to advanced understanding of the defense mechanisms in the hosts and discovery of genes and factors that affect host defense against insect pests (i.e., GB) in sorghum and related species. Objective 3: Develop improved germplasm of wheat, barley, and sorghum incorporating new sources of insect resistance and other desired traits into elite, adapted backgrounds for the United States. Subobjective 3.A. Develop high performance wheat, barley, and sorghum germplasm with enhanced resistance to GB, RWA, or BCOA, and release to the public. Subobjective 3.B. Develop genetically improved barley and sorghum cultivars and hybrids for use as feedstocks for bioethanol, animal feed, and forage-grazing potential under expanded growth conditions.
1b. Approach (from AD-416):
The long-term goal of this project is to provide wheat, barley, and sorghum producers with new pest resistant crops and technologies that will protect their crops from insect pests. To accomplish the research objectives, the project will search available germplasm collections to find new, effective sources of resistance to virulent aphid pests, including Russian wheat aphid (RWA), greenbug (GB), and bird cherry-oat aphid (BCOA). The genetic diversity and genetic control of resistance in these crops will be characterized using genetic and genomic approaches, leading to advanced understanding of the defense mechanisms in the hosts and discovery of genes and factors that regulate host defense against insect pests. The identified resistance genes will be transferred into elite, adapted genetic backgrounds. Plant genotyping will be conducted to map aphid resistance genes to the crop chromosomes and to develop molecular markers for marker-assisted selection to facilitate the breeding process. The research team of the project will work closely with collaborating plant breeding programs to obtain elite breeding lines to use as parents in backcrossing procedures to transfer aphid resistance and other value-added (e.g., enhanced ethanol production) traits. The genetically improved germplasm will be field-tested for agronomic and quality performance prior to release. The project will provide testing and selecting support to assure these desirable genes move through the various breeding programs on their way to the producers via cultivar and hybrid releases.
3. Progress Report:
A germplasm collection of 24,000 barley accessions in the National Small Grains Collection have been screened for resistance to bird cherry-oat aphid (BCOA). Resistant plants were rescued and seed increased in the greenhouse (this work relates to Objective 1A of the project). Crosses were made to transfer greenbug and bird cherry-oat aphid resistance to elite lines. Seed was increased for 16 genetic populations to determine the genetic diversity among greenbug resistant sources. Also, over 2,000 elite lines for resistance were screened for resistance to greenbug and Russian wheat aphid (RWA). Increased seed of 3,400 plants resistant to both aphids. Selected heads from 38 F2 populations to be screened in FY2017. Selected over 5,000 heads from 40 elite hulless and hulled lines for breeders seed increase prior to cultivar/germplasm release. Field evaluation of 103 elite lines at three locations in Oklahoma prior to cultivar release to the public. Four state survey to determine the adaptation of hedgehog grain aphid, a new pest introduction threatening U.S. small grain production. (This work relates to Objective 3B of the project.) To develop genetic sources for resistance to sugarcane aphids, a core collection of sorghum germplasm was selected from the approximately 40,000 germplasm accessions. This core collection was evaluated for their responses to sugarcane aphids (SCA) by artificially infestation in growth chambers. As a result, >10 sources with various levels of resistance (from strong to medium) to SCA were identified. In order to study the genetics of SCA resistance, several mapping populations were developed with the resistance germplasm lines. Genetic mapping with one of the mapping populations is progressing well towards the placement of the quantitative trait loci (QTLs) on sorghum chromosomes. At the same time the identified SCA resistant sources were crossed in order to move the resistance genes into elite lines. Evaluation of those genetic materials is underway. (These progresses relate to Objective 1 of the project.) A set of 17 wheat landraces have been identified to provide a high level of resistance to RWA biotype 2 by screening a large set of germplasm, and developing a 1-6 scale scoring system for RWA assay. The related paper was selected as one of the "2016 Outstanding Papers in Genetic Resource Award" by Crop Science Society of America. Also, about 1300 wheat accessions were screened for resistance to RWA biotype 3, leading to the identification of a set of resistant landraces. In addition, a few BCOA-resistant wheat germplasm were discovered by screening about 2700 wheat accessions, including one spring wheat that can be directly used in U.S. wheat breeding. We have screened about 3000 wheat accessions for greenbug resistance, and reselected a line with good resistance to greenbug. (The progresses relate to the Objective 1A of the project.) Under Objective 2 and 3, a number of sorghum populations with dual purposes (mapping and breeding) were developed and are being advanced toward isogenic lines. Also, four mapping populations were developed to map RWA2 resistance genes in four Iranian wheat landraces, and one F2:3 population was used to tag RWA2 resistance genes in PI 624151-1-2. Two mapping populations are being developed to map greenbug resistance genes. Three mapping populations are being developed to map greenbug resistance genes. One F4 population and three F2 populations are currently available.
1. Fine-mapping of candidate genes associated with Greenbug resistance in sorghum. Greenbug is a serious constraint to cereal crop production, particularly in the Midwest and Plain areas, and it causes significant economic loss to U.S. sorghum producers. During the past years, scientists at ARS in Stillwater, Oklahoma conducted a fine-mapping of the resistance quantitative trait locus (QTL) using near-isogenic lines (NILs) derived from a cross between a highly resistant variety, and a highly susceptible variety, BTx623, using SSR markers. This allowed us to narrow down the target genes in a small region (59-kb) of sorghum chromosome harboring 8 candidate genes. Putative function of these candidate genes has been assigned based on the genetic analysis. Thus, our results provide the baseline information for cloning greenbug resistance genes of sorghum, and the markers developed in this study will be useful for molecular breeding of greenbug resistant sorghum varieties. If greenbug resistance genes are successfully used to control greenbug damage on 4.955 million acres of the sorghum crops in this country, this technology can save the U.S. sorghum growers approximately $250 million annually.
2. Identified novel quantitative trait loci (QTL) for coleoptile length of wheat. Wheat coleoptile is critical for crop establishment because its length determines the maximum depth seeds can be sown. Wheat cultivars with long coleoptiles are preferred in the low-precipitation dryland regions of the Great Plains and Pacific Northwest, where deep sowing is required to utilize moisture in the soil for wheat germination. ARS researchers at Stillwater, Oklahoma, identified eight QTL for coleoptile length using the genome-wide association mapping approach, and three of them are novel loci. These QTL and the associated single nucleotide polymorphism (SNP) markers are valuable for genetic improvement of coleoptile length in wheat. Wheat accessions combining desirable traits, long coleoptile length and short plant height, were also identified, and can be used in wheat breeding.
Li, G., Xu, X., Bai, G., Carver, B.F., Hunger, R.M., Bonman, J.M. 2016. Identification of novel powdery mildew resistance sources in wheat. Crop Science. 56(4):1817-1830.
Armstrong, J.S., Mornhinweg, D.W., Payton, M.E., Puterka, G.J. 2016. The discovery of resistant sources of spring barley, Hordeum vulgare ssp. spontaneum, and unique greenbug biotypes. Journal of Economic Entomology. 109(1):434-438.