Location: Peanut and Small Grains Research Unit
2022 Annual Report
Objectives
Objective 1: Identify new germplasm sources of resistance to cereal aphids, including greenbugs, Russian wheat aphid, bird cherry-oat aphid, and other important insect pests, in wheat, barley, and sorghum.
Subobjective 1A. Evaluate available germplasm resources (U.S. germplasm collections and accessible exotic resources) to identify new sources resistant to insect pests [Russian wheat aphid (RWA), greenbug (GB), bird cherry-oat aphid (BCOA)], and other important insect pests in wheat, barley, sorghum, and related species.
Objective 2: Characterize the genes controlling pest resistance and other related traits that are important for sustainable cereal crop production.
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 and genes controlling the resistance to GB, RWA, SCA, and BCOA in wheat, barley, and sorghum.
Subobjective 2.C. Map genes conferring resistance to cereal aphids, and develop genomic tools for cloning and marker-assisted selection of aphid resistance genes.
Subobjective 2.D. Conduct functional genomics studies on host response to attack by GB and sugarcane aphids (SCA), 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 and SCA) in grain sorghum, forage sorghum, and related species.
Subobjective 2.E. Reveal the genetic architecture of BCOA resistance using genomewide association study (GWAS), and develop genomic tools to facilitate rapid introgression of aphid resistance genes into adapted germplasm.
Objective 3: Develop enhanced germplasm and new varieties of sorghum, wheat, and barley with resistance to insect pests.
Subobjective 3.A. Develop high performance wheat, barley, and sorghum germplasm with enhanced resistance to GB, RWA, SCA, or BCOA, and release to the public.
Subobjective 3.B. Develop winter malting barley germplasm and cultivars for the Great Plains with enhanced insect resistance.
Approach
Wheat, barley and sorghum are the major cereal grains in the United States but their production is often threatened by destructive aphid pests, specifically the Russian wheat aphid, greenbug, bird cherry-oat aphid, and sugarcane aphid. Identification of natural resistance and use of genetically pest-resistant cultivars and hybrids in an integrated pest management program are the most economical and environmentally sound methods to reduce the negative economic impact of these damaging aphids. The overall goal of this project is to develop high performance wheat, barley, and sorghum with resistance to aphid pests. To accomplish this goal, the project will search available germplasm collections to find new, effective sources of resistance to aphid pests that are notorious for overcoming resistance through biotype evolution. The genetic diversity and resistance mechanisms will be analyzed, and resistance genes will be characterized and transferred into adapted genetic backgrounds. Plant genotyping will be conducted to map aphid resistance genes to the crop chromosomes and to develop molecular markers to facilitate marker-assisted selection and map-based gene cloning. 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 traits. The genetically improved germplasm and varieties will be field-tested for agronomic and quality performance prior to release. The project will provide testing and selecting support to assure that these desirable genes move through the various breeding programs on their way to producers via improved cultivar and hybrid releases.
Progress Report
In the previous year, ARS scientists at Stillwater, Oklahoma, screened a group of exotic sorghum germplasm (consisting of more than 200 accessions) collected by the Indian sorghum community, and the primary evaluation showed some promising sources of resistance to sugarcane aphid (SCA). We continued this research effort in 2022 to re-evaluate them, thus allowing us to confirm four germplasm lines as new sources of resistance to SCA in sorghum. These resistance materials are particularly valuable for sorghum breeders, as the germplasm may contribute novel source of resistance to the U.S. sorghum gene pool. (Objective 1A)
To avoid or reduce the damage of sorghum crop caused by grain aphids, our research effort in the past year focused on searching for sorghum germplasm that carries resistance to multiple species of aphids, including greenbug (GB) and SCA. ARS scientists at Stillwater, Oklahoma, started screening a group of 400 sorghum accessions that represent a collection of diverse sorghum germplasm. The initial screening results demonstrated that some germplasm may possess the potential to protect sorghum plants against multi-types of aphids, which would be able to protect sorghum crops from multiple threats. Thus, the evaluation experiments will be continued to confirm the genetic resource of multiple resistance in sorghum. (Objective 1A)
Research continued with screening 2,500 barley accessions from the National Small Grains Collection (NSGC) for resistance to Bird Cherry-Out Aphid (BCOA). Sub-objective 2B: Six allelism tests were completed to determine genetic diversity for GB resistance in barley. Sub-objective 2C: A new gene for GB resistance was identified. Two recombinant inbred lines (RIL) populations were phenotyped to map GB resistance genes in barley. Seed of six RIL populations were increased in the greenhouse for future analysis. Objective 3A: 2,300 F3 head selections were screened to both Russian Wheat Aphid (RWA) and GB. 1,617 resistant F3 lines were rescued and increased in the greenhouse. Another 3,300 F3 selections were increased in the greenhouse. Resultant F4 lines will be evaluated in single rows in fiscal year (FY) 2023. Seed from 88 F1 populations was increased in the greenhouse to develop F2 populations for head selections in the field in FY 2023. 4,200 single rows were evaluated in the field for agronomics. 460 lines were selected, and grain yield and malting quality were measured. Superior performing lines will be evaluated in yield trials in FY 2023. 242 lines were evaluated in replicated yield trials at two locations in Oklahoma. Grain yield, test weight, and malting quality were measured. Superior lines will be evaluated in advanced yield trials in FY 2023. (Objective 1A)
Understanding the defense mechanisms and genes involved in host resistance is the key for improving sorghum lines by incorporating these genes into new lines. For this purpose, ARS scientists at Stillwater Oklahoma, performed molecular experiments to analyze the phenylalanine ammonia-lyase (PAL) genes in the sorghum plant in response to an aphid attack, as it plays a crucial role in plant adaptation to many other biotic and abiotic stresses. The results from our experiments indicate the sorghum PAL genes were induced by SCA infestation and PAL genes exhibited differential gene expression in susceptible and resistant genotypes. Furthermore, PAL activity assays showed upregulated expression of the PAL genes in a resistant genotype when compared to those in a susceptible genotype. This study suggests that it is necessary to examine the regulation of PAL gene expression during plant-aphid interaction to elucidate the defense role of PAL in sorghum against aphids. (Objective 2D)
The standard aphid assay protocol does not work for BCOA because of two reasons: (1) BCOA tends to leave infested plants before above-ground symptoms are observed in open spaces; and (2) the infested plants are vulnerable to environment change and often completely die overnight without known reasons in greenhouse conditions. ARS scientists at Stillwater, Oklahoma, developed a growth chamber-based BCOA assay protocol that not only facilitates the test plants to grow well, but also warrants their constant infestation, leading to reliable and repeatable test results. Using this protocol, we evaluated the responses of an association panel which was genotyped by over one million single nucleotide polymorphisms (SNPs) to BCOA infestation and identified a set of BCOA-resistant lines that have the potential to be used in wheat breeding. (Objective 2E)
In continuing research efforts, newly identified SCA resistance sources have been crossed into several elite sorghum lines for development of both mapping populations and breeding populations. Several resulted populations are being tested and the pedigree has been advancing simultaneously, and a couple of such populations have reached the final selection stage (i.e., recombinant inbred lines). The promising SCA inbred lines may be released once these important traits, including aphid resistance and other yield components, are characterized. (Objective 3A)
ARS scientists at Stillwater, Oklahoma, developed and released reselection lines PI 682675 and PI 697274. PI 682675 carries Dn10 conferring resistance to all major U.S. RWA biotypes, and PI 682675 carries Gb8 conditioning resistance to economically important biotypes B, C, E, H, I and FL. Both genes are essential for developing aphid-resistant wheat cultivars. (Objective 3A)
Accomplishments
1. Identification and analysis of aphid resistance genes in crop plants. Aphids such as greenbug and sugarcane aphid have been serious pests of many cereal crops, including sorghum, particularly in the southern U.S. Uncontrolled aphid colonies can kill young plants quickly and severely reduce yields in mature plants; so, the pest can pose a serious threat to our farmers and food supply. Recent studies by ARS scientists at Stillwater, Oklahoma, focused on the identification of plant resistance genes in sorghum plants using cutting-edge genomic tools. In the genome-wide analysis of plant-aphid interactions, 308 resistance (R) genes were discovered in the sorghum genome; subsequently, the gene structures and their phylogenetic relationship among the members of the R gene family were characterized through bioinformatic analysis. Furthermore, differential expression of those R genes responding to aphids were analyzed using both RNA Sequencing (RNA-Seq) and quantitative real-time PCR (qRT-PCR) technologies, leading to the identification of several important R genes that confer aphid resistance in sorghum. The information generated in this research advanced the understanding of the defense mechanisms in the hosts and the genes and regulatory factors that affect host defense against aphids in sorghum and possibly other related species. With a better understanding of the plant defense mechanisms and the available resistance genes, plant breeders can develop crops with improved resistance to aphid pests and the use of genetically resistant crop cultivars and hybrids contributes one of the most effective and environmentally sound approaches in insect pest management in modern agriculture.
2. Discovery of a new greenbug resistance gene, Rsg3, in Chinese landrace PI 565676. Greenbug (GB) (Schizaphis graminum Rondani) is a pest posing a serious threat to cereal production worldwide and yield losses caused by GB are predicted to increase due to global warming. Host plant resistance is preferred for controlling GB. However, only a few barley GB resistance genes have been reported and new genes are urgently needed because of the continuous occurrence of novel GB biotypes. ARS scientists at Stillwater, Oklahoma, identified a new GB resistance gene, Rsg3, in PI 565676, and developed user-friendly, high throughput Kompetitive Allele-Specific PCR (KASP) markers for its use in marker-assisted selection. Rsg3, which resides in the long arm of chromosome 3H, confers resistance to economically important GB biotypes B, F, TX1, WY4A, WY10 MC, and WY10B, and is valuable for breeding GB-resistant barley cultivars.
Review Publications
Shrestha, K., Huang, Y. 2022. Genome-wide characterization of the sorghum JAZ gene family and their responses to phytohormone treatments and aphid infestation. Scientific Reports. 12. Article 3238. https://doi.org/10.1038/s41598-022-07181-9.
Zhang, H., Huang, J., Huang, Y. 2022. Identification and characterization of plant resistance genes (R genes) in sorghum and their involvement in plant defense against aphids. Plant Growth Regulation. 96:443-461. https://doi.org/10.1007/s10725-022-00797-x.
Xu, X., Kolmer, J., Li, G., Tan, C., Carver, B.F., Bian, R., Bernardo, A., Bai, G. 2022. Identification and characterization of the novel leaf rust resistance gene Lr81 in wheat. Journal of Theoretical and Applied Genetics. Article 04145-5. https://doi.org/10.1007/s00122-022-04145-5.
Xu, X., Mornhinweg, D., Bernardo, A., Li, G., Bian, R., Steffensen, B.J., Bai, G. 2022. Characterization of Rsg2.a3: A new greenbug resistance allele at the Rsg2 locus from wild barley (Hordeum vulgare ssp. spontaneum). The Crop Journal. https://doi.org/10.1016/j.cj.2022.01.010.
Mornhinweg, D.W., Carver, B.F., Springer, T. 2022. Registration of 'USDA Fortress' winter feed barley with multiple aphid resistance. Journal of Plant Registrations. Article 20241. https://doi.org/10.1002/plr2.20241.
