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:
In an ongoing project to develop RWA/GB-resistant winter hulless feed barley varieties for the Southern Plains, evaluated 99 lines in a replicated yield trial at one location. Evaluated 2,352 plant rows in the field, and selected lines for yield trial evaluation in 2014. Selected 100/300 heads from each of 22 advanced generation lines for breeders seed. Screened 1,260 F3 to both GB and RWA, and selected 4,000 seedlings for increase in the greenhouse. Progeny testing of 16 spring and 24 winter BCOA-resistant lines to develop pure lines. 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. Made crosses to develop genetic populations that would allow for the determination of genetic diversity for resistance to GB and BCOA in barley. Inheritance study to determine the genetic control of RWA resistance in one resistant line. Obj. 1A. A worldwide collection of wheat cultivars, landraces, and genetic stocks (approx. 1400) was screened to identify novel aphid-resistant sources. Sixteen RWA2-resistant germplasm, including nine landraces and seven reselection lines, were identified. Results were summarized and submitted to Crop Science. Two genetic stocks offering a high level of resistance to BCOA were also identified. Obj. 1B. This objective is not pursued in wheat. Instead, a large set of germplasm was screened to identify those surviving a heavy BCOA infestation. Obj. 2B. 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. 3A. 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.
1. Identification of expression profiles using NGS technology. Greenbug (Schizaphis graminum) is the most important insect pest of grain and forage sorghums in the midwestern United States. ARS investigators at Stillwater, Oklahoma, utilized next generation sequencing (NGS) technology to examine the gene expression profiles of sorghum challenged by virulent greenbug in order to discover the resistant mechanisms and to improve the understanding of host plant and aphid pest interactions. The RNA-sequencing results revealed transcriptional activities of 27,130 unique genes from the sorghum plants challenged by greenbug. Out of these actively expressed genes, 897 were differentially expressed between the greenbug-resistant and -susceptible lines. Furthermore we successfully characterized many of the newly identified genes that were already assigned as plant defense factors as well as regulatory sequences. This study generated a substantial amount of sorghum transcript (i.e., genes) sequences, and the results contribute to the identification of candidate genes responsible for insect resistance in sorghum, which led to new insights into the molecular basis of the host defense against greenbugs and the new tools for insect resistance breeding in sorghum.
Dahleen, L.S., Mornhinweg, D., Bregitzer, P., Vitou, J., Cakir, M. 2014. Biotype differences for resistance to Russian wheat aphid in barley. Crop Science. 54:1505-1513.
Azhaguvel, P., Mornhinweg, D.W., Vidya-Saraswathi, D., Rudd, J.C., Chekhovskiy, K., Saha, M., Close, T.J., Dahleen, L.S., Weng, Y. 2014. Molecular mapping of greenbug (Schizaphis graminum) resistance gene Rsg1 in barley. Plant Breeding. 133(2):227-233.
Dong, W., Su, S., You, L., Huang, S., Qi, J., Lu, G., Huang, Y., Yang, Y. 2013. QTLs analysis of tillers number in F6 sorghum population. Journal of Nanjing Forestry University Natural Science Edition. 37(2):55-58.
Yan, L., Xia, G., Huang, Y., Zaho, S. 2013. Cinnamic acid 4-hydroxylase of sorghum [Sorghum biocolor (L.) Moench] gene SbC4H1 restricts lignin synthesis in Arabidopsis. Plant Physiology Journal. 49(12):1433-1441.
Kumar, A.A., Gorthy, S., Sharma, H.C., Huang, Y., Sharma, R., Reddy, B.V. 2014. Understanding genetic control of biotic stress resistance in sorghum for applied breeding. In: Wang, Y-H, Upadhyaya, H.D., Kole, C., editors. Genetics, Genomics and Breeding of Sorghum. Chapter 9. Boca Raton, FL: CRC Press. p. 198-225.