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. Over the next 5 years we will focus on the following objectives: 1: Discover new sources of genetic resistance to insect pests (Russian wheat aphid, greenbug, and bird cherry-oat aphid) in wheat, barley, sorghum, and related species; 2: Determine genetic control of resistance, genetic diversity of resistance, and characterize genetic mechanisms of resistance to insect pests in wheat, barley, and sorghum; and 3: Develop wheat, barley, and sorghum germplasm/varieties with resistance to insect pests, increased yield, and other value-added traits.
1b. Approach (from AD-416)
To accomplish the research objectives, the project will search available germplasm collections to find new, effective sources of resistance to virulent aphid pests. The genetic diversity and genetic control of resistance will be characterized, and resistance genes will be transferred into 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. 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 (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
Identifying new sources of aphid resistance in barley: New greenhouse screening technique for identifying BCOA resistance was tested to determine the accuracy of the technique in predicting resistance. One hundred seventy-seven accessions were phenotyped with RWA1 to determine genetic diversity of RWA resistance in resistant sources identified and germplasm lines released from our program. Studies of genetic control of aphid resistance: Genetic populations were developed to determine genetic diversity in 8 sources of greenbug (GB) resistance and 7 sources of RWA resistance. Inheritance of RWA resistance in 1 germplasm line was determined. Doubled haploid populations were phenotyped to determine inheritance of RWA resistance in 5 sources. Transfer of aphid resistance and other value-added traits into barley breeding lines: Hulless trait was transferred into aphid-resistant germplasm lines. Heads were selected from 231 F2 populations, and 3,285 hulless heads were screened for RWA/GB resistance. Over 4,000 F3 lines were increased. Over 3,000 RWA/GB-resistant hulless F4 lines were evaluated for agronomics and remnant seed screened to determine homozygosity of RWA/GB resistance. Developing and advancing sorghum breeding populations: GB-resistant pedigree was advanced further, and the segregating populations were screened to identify the most productive genotypes. Those selection processes are the essential steps toward the development of pure lines, resulting in new varieties of GB-resistant sorghum. Evaluating sweet sorghum germplasm to identify genetic stocks for bioethanol production: We collected 687 sweet sorghum varieties and conducted field studies to evaluate certain essential traits that contribute to the ethanol yield potential. These characteristics included plant height, sugar content, biomass yield, phenology of flowering, etc. The experiments are being repeated this year to ensure accuracy. Responses to greenbug feeding in sorghum lines with varied lignin content: Two sorghum BMR lines along with the wild type parent line were evaluated in the greenhouse. During this assay, all seedlings exhibited similar responses to the infestation by GB biotype I, which caused severe damage to all the seedlings tested. The results indicate that differential responses were due to the resistance nature of the host plants, but showed no differential response to GB feeding at the seedling stage between bmr lines and non-bmr lines. Genetic analysis of selected RWA-resistant wheat lines: Thirty-eight RWA-resistant accessions were evaluated for their response to feeding by RWA1 or RWA2. Simultaneously, they were genotyped using the AFLP technique. Data generated from both phenotyping and genotyping were used to determine their genetic diversity and relatedness among the resistant accessions. Developing technique to screen host plants resistant to multiple aphids: Using a new technique with sequential and combined screening (infesting first with RWA alone for about 7-10 days, then adding GBE), segregating wheat populations were successfully screened and wheat lines with combined resistant to RWA1, RWA2, and GBE were identified.
1. Identification of sorghum genomic regions contributing resistance to greenbug. Greenbug is an economically important insect pest to sorghum production, estimated to cause approx. $248 million in losses annually to sorghum growers in the US. Among various virulent greenbug biotypes, biotype I is the most predominant and severe on sorghum. In this study, ARS researchers at Stillwater, OK, identified three major and one minor genomic regions that contribute to greenbug biotype I resistance in sorghum on chromosome 9 and 3, respectively. These newly reported greenbug resistance regions are useful for screening germplasm collections for identifying new resistant sources, have opened the option of pyramiding multiple regions for resistance from those different sources, and can be used to enhance the sorghum breeding program through marker-assisted selection and map-based cloning.
2. Development of EST-SSR markers in sorghum and their transferability among cereal species. Rapid increase in the availability of expressed sequence tag (EST) data has facilitated the development of simple sequence repeat (SSR) markers for comparative genomics, gene discovery, and marker-assisted breeding in field crops. In this study, we identified 2,680 ESTs out of 25,456 that contained one or more SSRs. From these SSR-containing ESTs, a sub-set of 200 were randomly selected for validation of amplification, polymorphism in sorghum, and for their transferability to the model species Arabidopsis and related cereal crops such as maize, sugarcane, rice, wheat, and barley. The high reproducibility, transferability, and polymorphism that we found demonstratess the potential utility of these EST-SSR markers not only in sorghum, but in a wide variety of related crop species.
Mornhinweg, D.W. 2011. Biotic stresses in barley: Insect problems and solutions. In: Ullrich, S.R., editor. Barley: Production, Improvement, and Uses. Hoboken, NJ: Wiley-Blackwell. p. 355-390.