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:
Under Objective 1, in 2014 and 2015 a core collection of sorghum germplasm were evaluated for resistance to the sugarcane aphid, leading to identification of the resistance sources. In addition, 1700 wheat germplasm lines were screened and resistance sources were identified for RWA2 and RWA3, and 2700 accessions were screened and resistant lines were identified for resistance to greenbug (GB) and bird cherry-oat aphid (BCOA). Under Objective 2, crosses were made in barley; thus genetic populations were developed to determine genetic diversity for resistance to GB and BCOA in barley. So far, an inheritance study was completed, resulting in a better understanding of the genetic control of the Russian wheat aphid (RWA) resistance in one resistant line. Under Objective 3, in an ongoing project to develop RWA/GB resistant winter feed barley varieties for the Southern plains, 64 elite hulless barleys were evaluated for RWA/GB resistance and replicated yield trials of 35 elite hulled barleys were conducted at one location. A subset of these lines was also evaluated at two other locations in Oklahoma. In 2015, 2,548 plant rows were evaluated in the field and 75 heads were selected from each of 78 F3 populations and 200 heads from each of 7 advanced generation elite lines for breeders seed increase. We screened 4,600 heads to both RWA and GB and selected 3,600 seedlings for increase in the greenhouse. Eight genetic populations were developed to determine genetic diversity in those new resistant sources. Crosses were made to transfer BCOA resistance to susceptible, adapted spring barleys.
1. New, high yielding, barley cultivars 'RWA 1758' and 'Mesa' have resistance to Russian wheat aphid (RWA). Both spring and winter barleys played a significant role in crop rotations in drought prone western U.S. RWA, introduced into the U.S. in 1986, quickly spread through the high dry plains of the western U.S. All U.S. barleys were highly susceptible to RWA and barley production in many areas decreased or ceased. A program to develop RWA-resistant barleys for the U.S. was undertaken by researchers at the USDA-ARS in Stillwater, OK, in conjunction with USDA-ARS, Aberdeen, ID, and Colorado State University. The most recent releases, spring barley RWA 1758 and winter barley Mesa, have recently been licensed to private companies with seed sales topping 20,000 bu in 2015. Mesa and RWA 1758 fill the varied needs of small grains growers in the Western U.S.
2. Genome-wide association mapping revealed novel quantitative trait loci (QTL) for leaf rust resistance in wheat. Leaf rust, caused by P. recondita, is a major disease that regularly reduces 5-15% yield of susceptible wheat cultivars. Most of leaf rust resistance genes conditioned effective levels of resistance when first released, and lost resistance within a couple of years in the Great Plains. The short-lived nature of leaf rust resistance genes necessitates continuously discovering novel genes. ARS researchers at Stillwater, OK, identified 14 QTL for leaf rust resistance using the genome-wide association mapping approach. A set of 1537 germplasm collected from 85 countries was used in this study. Of these QTLs, six coincided with genes/QTLs previously identified in either bread or durum wheat, and the other eight were novel loci. These novel QTLs identified in this study represent a valuable tool for wheat breeding programs to fight this devastating pathogen.
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Xu, X., Bai, G., Carver, B.F., Zhan, K., Huang, Y., Mornhinweg, D.W. 2015. Evaluation and reselection of wheat resistance to Russian wheat aphid biotype 2. Crop Science. 55(2):695-701.
Puterka, G.J., Giles, K.L., Brown, M.J., Nicholson, S.J., Hammon, R.W., Peairs, F.B., Randolph, T.L., Michaels, G.J., Bynum, E.D., Springer, T.L., Armstrong, J.S., Mornhinweg, D.W. 2015. Change in biotypic diversity of Russian wheat aphid (Hemiptera: Aphididae) populations in the United States. Journal of Economic Entomology. 108(2):798-804.
Dahleen, L.S., Bregitzer, P.P., Mornhinweg, D.W., Esvelt Klos, K.L. 2015. Genetic diversity for Russian wheat aphid resistance as determined by genome-wide association mapping and inheritance in progeny. Crop Science. 55(5):1925-1933.