Location: Peanut and Small Grains Research Unit
2019 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
Previously identified sorghum germplasm lines for sugarcane aphid and/or greenbug were amplified in the field and rescreened in growth chambers, leading to confirm 46 sorghum lines with excellent resistance to sugarcane aphid and 2 lines to greenbug. (Objective 1A)
Two thousand accessions from the NSGC were screened as seedlings in the greenhouse for resistance to bird cherry-oat aphid. Survivors were rescued and grew in the greenhouse for increase of the resistant source. (Objective 1A)
We have assembled a core set of 172 RWA (Russian wheat aphid)-resistant wheat germplasm, and evaluated their responses to major RWA biotypes RWA1, RWA2, RWA3/7, RWA6, and RWA8. Wheat accessions resistant to multiple biotypes were identified, and 14 accessions exhibited resistance to all five biotypes. Crosses were made to derive breeding/mapping populations from these resistance sources, intending to characterize the underlying RWA resistance genes and introgress them into adapted germplasm. In addition, we continued to test bird cherry-oat aphid (BCOA) resistant germplasm we identified previously, and breeding/mapping populations are being developed from these germplasms. (Objective 1A)
Four inter-crossed sorghum populations have been developed from different resistance sources with aphid resistance trait, which will be used for allelism testing to determine whether the aphid resistance among those unrelated germplasm lines is controlled by the same gene or more than one gene coding for the same trait, aphid resistance. (Objective 2B)
We have characterized the greenbug (GB) resistance gene in wheat reselection line PI 595379-1, permanently designated Gb8, and mapped Gb8 to an interval of 2.7 Mb interval in the terminal bin of chromosome 7DL (7DL3-082-1.0), spanning 595.6 to 598.3 Mb in the Chinese Spring IWGSC RefSeq v1.0 reference sequence. An SSR marker co-segregating with Gb8 was also developed for marker-assisted selection. Allelism tests indicated that Gb8 is a new gene different from three permanently named genes on the same chromosome arm. Gb8 confers a broader range of resistance than other known genes, and can be directly used in wheat breeding to enhance resistance to agronomically important greenbug biotypes B, C, E, H, I, and FL. (Objective 2C)
One of our research efforts aimed at identification of genes and gene products that are related to the host plant defense against aphids, gene expression profiles of sorghum seedlings in response to greenbug infestation were generated using RNA-seq technology. According to the result obtained, gene expression profiling offers new insights and tremendous promise for dissecting the host defense and molecular resistance mechanisms. (Objective 2D)
For improving sugarcane resistance in sorghum, 27 new crosses have been made in this year in order to transfer the resistance into those genetically improved background of sorghum, which are being used to develop sugarcane aphid resistant germplasm/new cultivars. (Objective 3A)
In a continuous effort for sorghum genetic improvement, several resistance sources have been crossed into elite sorghum lines for development of both mapping populations and breeding populations. In this year eight populations have been further advanced to F4 or F5 generations, and some of the promising SCA inbred lines can be released within 1-2 years. (Objective 3A)
Seedlings from 50 heads selected from each of 70 F3 populations were screened in the greenhouse to both RWA and greenbug towards the development of winter feed barley for the southern plains. The resulting 4,681 F4 selections homozygous resistant for RWA and GB were increased and harvested in the greenhouse in the spring of 2019. These lines will be evaluated as single rows in the field in 2020. Two thousand homozygous resistant F4 harvested in the greenhouse in 2018 were evaluated in single rows in the field in 2019. Advanced yield trials were conducted in 2 locations in Oklahoma as well as with cooperators in Kansas and Nebraska. An advanced yield trial was conducted for Virginia Poly Tech at one location in Oklahoma. (Objective 3A)
Efforts in 2019 towards development of winter malting barley for the Great Plains included head selections in the field from 96 F2 populations, the increase of 181 F1 to F2 in the greenhouse and 319 crosses made in the spring of 2019. (Objective 3B)
Accomplishments
1. Release of sorghum lines resistance to sugarcane aphid and greenbug. Sugarcane aphid is a new invasive pest of sorghum and causes severe damage to sorghum, resulting in a big loss of production to sorghum producers, i.e. $742.7 million in 2015. Recently we made, great research effort on searching germplasm resources for resistance to this devastating aphid through evaluation of a large collection of sorghum germplasm, thus our research has led to the identification of resistant materials and subsequently incorporation of the genetic resistance to sorghum breeding materials through traditional crossing breeding approach. As a result of this work, two breeding lines have been released, STARS 1801S with genetic resistance to both sugarcane aphid and greenbug and STARS 1802S with resistance to sugarcane aphid and head smut disease. These new resistant sources are already available to the sorghum community and will contribute directly to genetic improvement of sorghum for crop protection from these important pests. The result of these resistance cultivars can successfully help sorghum producers to safeguard their crops from the severe aphid pest.
2. Quantitative trait locus (QTL) mapping and molecular characterization of sugarcane aphid resistance genes in sorghum. Host plant resistance is a genetic mechanism for effective control of sugarcane aphid (SCA) in sorghum. Mapping genes for resistance to the SCA is essential to understand the molecular basis of the host plant defense in sorghum. A mapping population was developed by crossing an elite line, BTx623 (susceptible parent) with a resistant donor (sugarcane aphid resistant line), then the resulted population was genotyped using Simple Sequence Repeat (SSR) markers. Simultaneously, all F2:3 progenies were evaluated by screening their response to virulent SCA in growth chambers. Through correlation studies between the phenotyping and genotyping data, linkage relationship between SSR markers used in genotyping and SCA resistance loci in sorghum genome was established, then the resistance QTL was mapped to a specific location of the chromosome 6. Importantly SSR markers closely-linked to the resistance QTLs and identification of the chromosomal regions responsible for sugarcane aphids will greatly contribute to both map-based cloning of the resistance genes and marker-assisted breeding of new hybrids or cultivars with genetic resistance to sugarcane aphids.
3. Release of Winter Feed Barley Cultivar "Fortress" resistant to both Russian wheat aphid and greenbug. Small grain producers in the southern plains are seeking an alternative to wheat. Greenbug and Russian wheat aphid are a threat to small grains in this area. Although historically produced in the southern plains, there has not been a barley variety released for this area since 1980. Barley is a good feed source for animals both for grazing and grain. Resistant varieties are an environmentally and economically sound solution to aphid attack. Russian wheat aphid resistant sources were crossed into a greenbug-resistant winter feed barley adapted to the southern plains. Many years of screening for aphid resistance and repeated crossing followed by many years field evaluation at several locations in Oklahoma resulted in the selection of one superior preforming line that was resistant to both Russian wheat aphid and greenbug. Fortress is the first barley variety resistant to both Russian wheat aphid and greenbug in the U.S. Growers not only have an alternative to wheat for small grain production, but they have the added advantage of reduced economic and environmental expense. There will be no need for seed treatment and/or field spraying of insecticides with Fortress.
4. Identification and characterization of Pm63, a new powdery mildew resistance gene in wheat. Powdery mildew, caused by Blumeriagraminis f. sp. tritici (Bgt), is the most common and widespread disease in wheat. Yield losses of 5 to 8% were estimated for average powdery mildew infection and up to 30% in years of severe epidemics. Bgt races evolve rapidly and many powdery mildew resistance genes have lost their effectiveness in southern Great Plains. ARS scientists at Stillwater, Oklahoma, discovered a novel powdery mildew resistance gene, officially designated Pm63, in Iranian landrace PI 628024, and mapped Pm63 to the terminal region of the long arm of chromosome 2B. Pm63 confers a broad spectrum of resistance to Bgt isolates in the U.S. and can be widely used in U.S. wheat breeding programs to enhance powdery mildew resistance.
5. Identification and characterization of Pm65, a new powdery mildew resistance gene in wheat. Undernourishment is a globally growing problem with one of nine persons suffering from chronic hunger. The adoption of high-yield intensive-management systems, as well as the projected 1–3.7 degree increase in average global temperature by the end of this century, will likely increase the incidence and severity of powdery mildew, a globally common wheat disease causing 5 to over 30% of yield losses each year. New powdery mildew resistance genes that can be directly used in wheat breeding are urgently needed. ARS scientists at Stillwater, Oklahoma, discovered a novel powdery mildew resistance gene, officially designated Pm65, in Chinese wheat cultivar Xinmai208, and mapped Pm65 to the terminal region of the long arm of chromosome 2A. Coming from a high-yield potential cultivar, Pm65 can be directly used to enhance powdery mildew resistance in wheat. The newly developed SSR markers Xstars355 and Xstars356 can facilitate the introgression of Pm65 into elite U.S. cultivars.
6. Identification and characterization of Gb8, a novel greenbug resistance gene conferring a wider spectrum resistance in wheat resection line PI 595379-1. Greenbug is a worldwide insect pest that poses a serious threat to wheat production. The annual economic loss caused by greenbug on cereal crops in the Great Plains of the USA likely exceeds $100 million. New greenbug resistance genes that can be readily used in wheat breeding are urgently needed. ARS scientists at Stillwater, Oklahoma, discovered a novel greenbug resistance gene, designated Gb8, in wheat resection line PI 595379-1 and located it to the terminal region of the long arm of chromosome 7D. An SSR marker co-segregating with Gb8 was also developed to rapidly transfer Gb8 into elite cultivars using marker-assisted selection. Gb8 confers a broader range of resistance than other known genes, and can be directly used in wheat breeding to enhance resistance to agronomically important greenbug biotypes B, C, E, H, I, and FL.
7. Identification and characterization of Dn10, a new gene conferring resistance to Russian wheat aphid biotype 2. Russian wheat aphid (RWA) is a serious pest of wheat and barley that causes heavy yield losses in many countries, and RWA caused over $1 billion in damage and control costs in western region of the USA from 1986 to 1997. The occurrence of RWA biotype 2 (RWA2) in the USA rendered most RWA resistance genes ineffective. New RWA resistance genes are urgently needed to manage RWA2. ARS scientists at Stillwater, Oklahoma, discovered a novel RWA-resistant gene, officially designated Dn10, in Iranian landrace PI 682675. Dn10 confers high resistance to RWA2 and should be widely used in wheat breeding to enhance RWA resistance.
Review Publications
Li, G., Carver, B., Cowger, C., Bai, G., Xu, X. 2018. Pm223899, a new recessive powdery mildew resistance gene identified in Afghanistan landrace PI 223899. Theoretical and Applied Genetics. 131(12):2775-2783. https://doi.org/10.1007/s00122-018-3199-y.
Tan, C., Li, G., Cowger, C., Carver, B.F, Xu, X. 2019. Characterization of Pm63, a new powdery mildew resistance gene identified in Iranian landrace PI 628024. Journal of Theoretical and Applied Genetics. 132(4):1137-1144. https://doi.org/10.1007/s00122-018-3265-5.
Li, G., Xu, X., Tan, C., Carver, B.F., Bai, G., Wang, X., Bonman, J.M., Wu, Y., Hunger, R., Cowger, C. 2019. Identification of powdery mildew resistance loci in wheat by integrating genome-wide association study (GWAS) and linkage mapping. The Crop Journal. 7(3):294-306. https://doi.org/10.1016/j.cj.2019.01.005.
Puterka, G.J., Hammon, R.W., Mornhinweg, D.W., Springer, T.L., Armstrong, J.S., Brown, M.J. 2019. Distribution of a new invasive species, Sipha maydis Passerini (Heteroptera: Aphididae), on cereals and wild grasses in the Great Plains and Rocky Mountain states. Journal of Economic Entomology. 112(4):1713-1721. https://doi.org/10.1093/jee/toz068.
