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:
This project was terminated on February 2018 and replaced with project 3072-21000-009-00D. Over 10,000 wheat germplasm were screened for resistance to greenbug (Gb), Russian wheat aphid (RWA), and bird cherry oat aphid (BCOA), and identified one resistant accession for greenbug, three for BCOA, and 20 for RWA. Crosses have been made to develop mapping populations and transfer resistance genes to adapted germplasm (Objective 1A). We have identified the novel RWA resistance gene Dn10. We have discovered 3 novel powdery mildew resistance genes conferring high resistance to Blumeria graminis f.sp.tritici (Bgt) isolates collected from the Great Plains. We have developed a recombinant inbred line (RIL) population using a BCOA resistance accession we identified, and molecular characterization of quantitative trait locus (QTL) for BCOA resistance is underway. (Obj. 1A) Rescreening of a core set (78 lines) of aphid resistance sorghum lines, which was selected from previous screening with sugarcane aphid. Results confirmed many lines carry the genetic resistance to sugarcane aphids, however, some of those lines were segregating for sugarcane aphid resistance. (Obj. 1A) Screened entire NSGC of winter barleys to BCOA. (Obj. 1A) Molecular mapping project to determine the genetic diversity within USDA-ARS released RWA resistant sources to world biotypes of RWA. Development of genetic populations to determine inheritance and genetic diversity of 8 new greenbug resistant sources. (Obj. 2B) Release of 2 GB resistant germplasm lines with Rsg2 resistance. Also release of 8 RWA and GB resistant hulless winter feed barley germplasm. (Obj. 3A) Release of Mesa first RWA resistant winter feed barley – licensed to Sauter Farms. In addition, field Evaluation of elite dual aphid (RWA and GB) resistant winter feed barley lines adapted to the southern plains and breeders seed increase prior to cultivar release. (Obj. 3B) We have screened a large set of wheat germplasm for bird cherry-oat aphid (BCOA) resistance, and identified two new resistance sources, which were subsequently used to derive mapping/breeding populations (Obj. 1A). Characterized a gene conferring resistance to Russian wheat aphid biotype 2 (RWA2) in PI 682675, a reselection line we developed from the Iranian landrace PI 624151. Our results suggested that the RWA2 resistance gene in PI 682675 is a new gene, designated as Dn10. Six powdery mildew resistance genes in wheat landraces and historical cultivars have been mapped using molecular markers. One of these genes has been designated as Pm59. We have developed a recombinant inbred line (RIL) population to map QTL for BCOA resistance in a resistant germplasm we previously identified (Obj. 2C). Approximately 7,000 barley accessions from the USDA-ARS National Small Grains Collection have been screened for resistance to BCOA. Surviving seedlings were increased in the greenhouse. And utilized in crossed. Aphids were collected in the field in multi-state survey over 2 years to determine the adaptation of a new invasive aphid pest (Hedgehog Grain Aphid) of small grains in the U.S. More than 30 sorghum germplasm lines have been identified as the new sources of resistance to sugarcane aphid (SCA) following screening of a large group of diverse sorghum germplasm accessions. Most of these lines have been purified and many of them have been amplified prior to germplasm release (Obj. 1A). Genetic characterization and agronomic evaluation in the field of the newly discovered germplasm is underway. Once released, these should benefit both private and public breeding programs. Using the genomic approach, we have mapped a major gene that offers the genetic resistance to SCA. We are developing DNA markers tightly linked to the resistance that can facilitate both marker-assisted breeding and cloning the SCA resistance genes in sorghum. (Obj. 2B) Two hundred crosses were made between winter feed barley cultivars adapted to the Southern Plains and elite winter malting barley germplasm/cultivars from several northern states to begin the development of winter malting barleys for the Great Plains (Obj. 3B). We continued to evaluate breeding populations in the field to select high yielding aphid-resistant lines, with an emphasis on greenbug and RWA resistance. (Obj. 3A) In addition, several resistance sources have been crossed into elite sorghum lines, including BTx623, for development of both mapping populations and breeding populations. Now a couple of such populations are already at F5 or F6 generation (i.e., recombinant inbred lines). Some of the promising SCA inbred lines can be released within 1-2 years. (Obj. 3B) Seven thousands of the 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 (Obj. 1A). Crosses were made to transfer bird cherry-oat aphid resistance to elite lines. Seed was increased for 80 genetic populations to determine the genetic diversity among greenbug resistant sources in barley. (Obj. 2B) Each year of the project 50-100 barley heads were infested from 65-80 F2 populations in the field. All heads were infested with both RWA and GB and resistant seedlings increased. Lines were evaluated in the field trials and multiplied. Superior lines have been released as germplasm and one as cultivar. (Obj. 3B) 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 using a 1-6 scale scoring system for RWA assay developed in this project. The related paper was selected as one of the "2016 Outstanding Papers in Genetic Resource Award" by Crop Science Society of America. 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 germplasms 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. (Obj. 1A) 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. Replicated greenhouse study to assess BCOA resistance in terms of grain yield and yield components. Field evaluation in a cooperative study with CSU to determine the economic injury level for three RWA-resistant germplasm lines with varying levels of seedling resistance. A worldwide collection of wheat cultivars, landraces and genetic stocks (about 1400) were screened to identify novel aphid- resistant sources. Sixteen RWA2-resistant germplasm, including nine landraces and seven reselection lines, were identified. Two genetic stocks offering a high level of resistance to BCOA were also identified. (Obj. 1A) Six crosses were made to derive mapping populations with newly identified resistance sources. Plans are to map BCOA-resistance genes in two germplasm, and RWA2 resistance genes in four landraces in 2014 FY. (Obj. 2B) About 2000 F5 or F6 head rows were evaluated for resistance to GB E and RWA2. A total of 450 lines resistant to both GB E and RWA2 was selected for further yield tests. (Obj. 3A) Studies of genetic control of greenbug resistance in sorghum: Crosses were made and genetic populations developed to determine genetic diversity in 5 sources of greenbug (GB)-resistant sorghum lines. These included traditional genetic populations and mapping populations. Mapping greenbug resistance genes in sorghum: New markers, SSR and gene specific markers, were developed to shorten the distance between DNA markers and the QTLs linked to the greenbug resistance; thus. Analysis of potential candidate genes in the chromosomal location is underway. Completed a cooperative study to determine differential response of 8 potentially new sources of resistance in barley to 14 greenbug biotypes/isolates. Evaluation of a breeding population of wheat: We have selected about 800 F5 lines from progenies of a cross designed to combine RWA resistance, GB resistance and high yield, OK03825-5403-6/OK05511//OK05212. We plan to evaluate their resistance to GB and RWA in greenhouses, and yield potential in the field in FY2014.
1. Identification and characterization of Pm223899, a novel recessive powdery mildew resistance gene in wheat. Wheat powdery mildew, a globally important disease caused by the biotrophic fungus Blumeria graminis f.sp.tritici (Bgt), has occurred with increased frequency and severity in recent years, and some widely deployed resistance genes have lost their effectiveness. ARS scientists at Stillwater, Oklahoma identified a new gene conferring high resistance to representative Bgt isolates collected from Pennsylvania, Oklahoma, Nebraska, and Montana in Iranian landrace PI 223899, designated Pm223899, and mapped Pm223899 to an interval of less than 1 Mb in the terminal region of chromosome 1AS. Pm223899 can be widely used to enhance wheat powdery mildew resistance in the Great Plains, Pennsylvania, and Montana.
Tan, C., Li, G., Cowger, C., Carver, B.F., Xu, X. 2018. Characterization of Pm59, a novel powdery mildew resistance gene in Afghanistan wheat landrace PI 181356. Theoretical and Applied Genetics. 131(5):1145-1152. https://doi.org/10.1007/s00122-018-3067-9.
Mornhinweg, D.W., Armstrong, J.S., Puterka, G.J. 2017. New greenbug resistant sources in winter barley, Hordeum vulgare (L.). Southwestern Entomologist. 42(3):619-626.
Li, H., Huang, Y. 2017. Expression of brown-midrib in a spontaneous sorghum mutant is linked to a 5'-UTR deletion in lignin biosynthesis gene SbCAD2. Scientific Reports. 7:11664. https://www.nature.com/articles/s41598-017-10119-1#Abs1.