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.
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.
1,000 barley accessions from the National Small Grains Collection were screened for bird cherry-oat aphid resistance. (Objective 1A) We evaluated a set of T. monococcum and T. urartu accessions for resistance to greenbug (biotype B), Russian wheat aphid (biotype 2), leaf rust (race Pt52-2), and powdery mildew (isolate B3.1). Resistant accessions were identified for each disease and pest, and five of them exhibited high resistance to all of them. Crosses were made to develop mapping population and transfer the underlying resistance genes in these accessions to elite breeding lines. (Objective 1A) In support of Objective 2C, we developed about 50 pairs of new primers based on the available genome sequences of sorghum in the DNA databases. Those primers generate simple sequence repeats (SSR) markers, which are used for fine-mapping quantitative trait loci (QTLs) in sorghum. (Objective 2C) During the current year, our continued effort focused on the development of more DNA markers to allow mapping and linkage analysis of QTLs responsible for resistance to greenbug (GB) and/or sugarcane aphid in sorghum. DNA markers developed in this project have proved their usefulness in screening germplasm and genetic materials for aphid resistance, suggesting that they can facilitate marker-based selection in sorghum breeding. (Objective 2C) Seed was provided for DNA sampling of 3 recombinant inbred line (RIL) populations and plants were increased after sampling. 3 RIL populations were phenotyped for greenbug resistance and 561 homozygous resistant seedlings selected for increase in the greenhouse. (Objective 2C) We reported the new greenbug resistance gene Gb8, which provides high resistance to a considerable number of economically important greenbug biotypes. Crosses were made to transfer Gb8 into elite breeding lines. We also initiated a project aimed at developing germplasm resistant to most economically important greenbug biotypes by combining Gb8 and Gb1. Gb1 is a recessive gene conferring unique resistance to some important greenbug biotypes. The recessive nature necessitates the use of marker-assisted selection to achieve the project goal. Therefore, we started to map Gb1 using a segregating population derived from DS28A Custer. We have evaluated the population for responses to greenbug biotype F and genotyped the population with single nucleotide polymorphisms (SNP) and simple sequence repeats (SSR) markers. Our preliminary results indicated that Gb1 resides on chromosome 1A. We expect to develop SSR and Kompetitive Allele Specific PCR (KASP) markers closely linked to Gb1 at the end of fiscal year 2020. In addition, we characterized the greenbug resistance gene Gb5 and developed three diagnostic KASP markers that can reliably select Gb5 in wheat breeding. (Objective 2C) In order to search for plant defense proteins and enzymes in sorghum plants, we conducted experiments to construct differential expression profiles at the protein level. Sorghum seedlings of both resistant and susceptible lines were infested with greenbugs (GB), from which total proteins were extracted and analyzed using the proteomic approach. In this way, differentially expressed proteins were identified from the resistant plants in comparison with susceptible control. The information generated from this study will contribute to a understanding of genetic mechanisms underlying host plant defense against pest aphids, greenbug in particular. (Objective 2D) 4,200 lines were screened to both Russian wheat aphid (RWA) and greenbug. 5,752 resistant selections from screening were grown and harvested in the greenhouse for field evaluation in fiscal year 2020 150 crosses were made among 172 second filial generation (F2) of one population. (Objective 3A) 3,378 single rows were planted for evaluation at one location, 183 F2 populations were planted for head selection at one location, and advanced yield trials were planted at 2 locations. 30 heads were selected from each F2 population, heads were threshed and seed counted. All locations were harvested and grain yield, test weight and percent plump and thin kernels were measured. 154 F2 populations were increased and harvested in the greenhouse for head selection in fiscal year 2020. (Objective 3B)
1. Development of genetic transformation system for sorghum. Sorghum improvement has mainly relied on traditional breeding methods, which have been successful in developing genetic improved hybrids and cultivars. However, conventional breeding is often too slow to achieve certain breeding goals or is limited because some genetic traits may not available in sorghum. Very recently ARS scientists at Stillwater, Oklahoma, have successfully developed a cutting-edge technology for designing and creating new varieties of sorghum with desired traits. This new technology is based on a gene transfer system using immature inflorescences of sorghum as the targets, to which any desirable genes can be delivered and installed using a gene gun or the Agrobacterium-mediated transformation system. The resultant transgenic plants appeared normal in morphology and fully fertile. This method represents a simple and efficient method for genetic transformation of sorghum that can speed up and facilitate the process of engineering new varieties in sorghum. This technology provides us an alternative tool for sorghum breeding and can complement conventional plant breeding; thus beneficial to crop breeders and sorghum producers.
2. Release of 'Fortress' six-rowed winter barley. Producers in the Southern Plains are looking for alternatives to wheat production. Winter barley has been grown successfully in the past. Both greenbug and Russian wheat aphid are potential pests in the Southern Plains. Fortress is the first U.S. barley variety resistant to both these aphids and to a new invasive species, hedgehog grain aphid, which has the potential to adapt to the Southern Plains. Insecticide applications for aphid control are both environmentally detrimental and an economic burden to producers. Fortress was developed by ARS in Stillwater, Oklahoma, by crossing greenbug resistant variety, Post 90, with a Russian wheat aphid (RWA)-resistant source. After 14 years of field evaluation in multiple locations in Oklahoma, Fortress was selected for release. Fortress will be co-released with Oklahoma State University. Fortress is high yielding with multiple aphid resistance and good disease and drought resistance. Aphid resistance in Fortress is tolerance, which means aphids survive on the plants but do not reduce grain yield thus having no negative effect on the food chain. Fortress provides an excellent alternative to wheat for small grain producers in the Southern Plains.
3. Development and validation of KASP markers for the wheat greenbug resistance gene Gb5. Greenbug [Schizaphis graminum (Rondani)] is a destructive pest of wheat worldwide, and incorporation of new greenbug resistance genes in wheat breeding pipelines is critical for sustainable wheat production. Although the greenbug resistance gene Gb5 confers resistance to several economically important greenbug biotypes, it has not been used in wheat breeding yet, partially due to the lack of efficient genomic tools to select the wheat-T. speltoides chromosome segment where Gb5 resides. ARS scientists at Stillwater, Oklahoma, characterized the wheat-T. speltoides chromosome segment and developed three Kompetitive Allele Specific PCR (KASP) markers for Gb5. These markers were validated in a recombinant inbred line population and a set of newly released wheat breeding lines, and the results indicated that they can greatly facilitate the introgression of Gb5 into adapted breeding lines.
4. Characterization of incomplete leaf rust resistance gene and development of KASP markers for leaf rust resistance gene in wheat. Leaf rust is one of the most common wheat diseases worldwide, and most known leaf rust resistance genes have lost effectiveness in the Great Plains of the United States. Therefore, new leaf rust resistance genes are urgently needed to enhance leaf rust resistancen. ARS scientists at Stillwater, Oklahoma, identified an incomplete leaf rust resistance gene, designated QLr.stars-1BS, on the short arm of chromosome 1B in the Chinese wheat cultivar Bainong 418, and characterized the leaf rust resistance gene Lr47, which is one of a few leaf rust resistance genes that are still effective in the Great Plains. One and two diagnostic Kompetitive Allele Specific PCR (KASP) markers were further developed for QLr.stars-1BS and Lr47, respectively, and these markers can facilitate the introgression of Lr47 and QLr.stars-1BS into elite wheat cultivars or breeding lines.
5. Identification of wheat germplasm resistant to major Russian wheat aphid biotypes in the United States. Russian wheat aphid (Diuraphis noxia Kurdjumov (RWA) is one of the most invasive and detrimental pests, and host plant resistance is the most efficient approach to manage RWA. Five major RWA biotypes were previously identified in the U.S., but wheat accessions resistant to RWA biotype 3 (RWA3), biotype 6 (RWA6), and biotype 8 (RWA8) have not been identified from the USDA-ARS National Small Grains Collection. ARS scientists at Stillwater, Oklahoma, evaluated the responses of a set of wheat accessions to these predominant U.S. biotypes—RWA1, RWA2, RWA3, RWA6, and RWA8—in controlled environments, and identified 14 accessions resistant to all five biotypes. These RWA-resistant accessions are valuable sources for breeding RWA-resistant wheat cultivars.
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