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
Develop and advance sorghum breeding populations: In previous work, the breeding population was developed by crossing a resistant germplasm (PI550607) to Westland to transfer the greenbug trait into the elite sorghum line. This year, the pedigree was advanced further, and the segregating populations were screened to identify the most productive genotypes. Genotyping sorghum mapping populations using SSR markers: To identify new genes of greenbug resistance in sorghum, a mapping population was developed by crossing BTx623 with a resistant line. Both genotyping and phenotyping experiments were completed this year. Eighty-four SSR markers were mapped on to sorghum chromosomes with 15 linkage groups. A linkage map was constructed, covering total length of 903.4 cM across the genome. Marker analyses showed 4 major QTLs on chromosome 9, explaining phenotypic variance between 8 and 30%. Evaluation of sorghum germplasm to identify genetic stocks or traits potential for bioethanol production: Sweet sorghum has not been bred and selected for ethanol production. Thus, we collected 687 sweet sorghum varieties and conducted field studies to evaluate certain essential traits that will contribute to the ethanol yield potential. These characteristics included plant height, sugar content, biomass yield, phenology of flowering. Experiments are being repeated next year to ensure accuracy. Screening of wheat germplasm for resistance to multiple biotypes of RWA: Screened single plant selections for homogeneity of RWA2 resistance prior to variety release. This potential variety release will be from further selections made within our germplasm release STARS-0601. These lines continue to have the highest level of resistance to multiple biotypes of RWA that has been identified to date. Identification of new sources of aphid resistance in barley: Three accessions were identified with resistance to GB biotype E from a collection of 360 wild barley accessions. Five potential new sources of GB resistance were purified. A new technique and rating scale for identification of BCOA resistance was tested. Studies of genetic control of RWA resistance: Genetic populations were developed to determine genetic diversity of GB resistance in 7 newly identified sources of resistance to GB biotype E. Inheritance of RWA resistance in one germplasm line was determined. Ninety-six RWA-resistant germplasm lines were phenotyped for an association mapping study to identify lines with candidate regions and linked markers for resistance. Transfer aphid resistance and other value-added traits into barley breeding lines: The hulless trait was transferred into dual aphid-resistant germplasm. Heads were selected from 111 F2 populations segregating for RWA and GB resistance, and hulless. Two thousand hulless F2 head selections were screened for RWA and GB, and 4,000 F3:F4 were increased in the greenhouse. Four thousand RWA/GB-resistant hulless F4 plant rows were evaluated in the field and 400 lines selected for further testing. F1 populations were increased to the F2 in the greenhouse. Eight winter barley RWA/GB-resistant lines were evaluated for agronomics prior to germplasm release in 2010.
1. Determination of genetic diversity for Russian wheat aphid resistance in barley: RWA, a devastating pest of small grains, was introduced to the US in 1986 and quickly adapted to the western US small grains production areas. All US barley cultivars were susceptible to RWA in 1986. Four RWA-resistant, spring feed barley cultivars have been developed and released cooperatively with the USDA-ARS and various state experiment stations. Since 2003, 7 new biotypes of RWA have been reported which overcome resistance in previously resistant wheat cultivars. Resistance in barley has held up to these new biotypes but deployment of different genes for resistance is essential to provide protection for future biotype changes. Inheritance studies for 2 germplasm lines whose resistance has been deployed in resistant cultivars indicated 2 gene control of resistance in each line. A cooperative molecular mapping study just completed has shown that these lines do differ in their genetic control of resistance. Genetic diversity in these lines (and their deployed cultivars) increases the durability of protection against potential new RWA biotypes.
2. Identification of greenbug resistant barley accessions: Greenbug is a major crop pest to small grains in the Southern plains especially in outbreak years. Two single dominant genes have been identified in barley, which provides resistance to the predominant greenbug biotypes. New biotypes have recently been reported that can overcome these sources of resistance. The large amount of genetic diversity existing in greenbugs harbored on native grasses in the US makes the likelihood of new biotypes a surety for the future. In a separate screening, three accessions of wild barleys from the Wild Barley Diversity Collection and five hulless winter barley accessions identified as resistant to greenbug biotype E were screened with all known biotypes of greenbug, and their differential response indicated that resistance in these lines differs from previously identified resistance genes. All 8 newly identified greenbug-resistant lines will be genetically tested to determine if they do indeed possess unique genes for greenbug resistance. Novel genes are essential to protect winter small grains from crop production loss by new greenbug biotypes.
3. Sweet sorghum a candidate for ethanol production: Sweet sorghum has the potential to be used as a renewable energy crop and has become a viable candidate for ethanol production. However, characterization of the sweet sorghum germplasm and their genetic improvement are behind the current demand. To initiate this research effort, we collected 687 sweet sorghum varieties and conducted field studies to evaluate certain essential traits that will contribute to the ethanol yield potential. These characteristics, including plant height, sugar content, biomass yield, phenology of flowering, were analyzed. The resultant data represent the first document for the 687 sweet sorghum lines on their biological characteristics and agronomic traits, which are very useful to sorghum breeders in selecting breeding materials.
Mornhinweg, D.W., Bregitzer, P.P., Porter, D.R., Peairs, F.B., Baltensperger, D.D., Hein, G.L., Randolph, T.A., Koch, M., Walker, T. 2009. Registration of 'Sidney' spring feed barley resistant to Russian wheat aphid. Journal of Plant Registrations. 3(3):214-218.