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
Identification of new sources of aphid resistance in barley: Over 1,000 barleys from the NSGC were screened to greenbug. Spring barley lines from 10 national barley breeding programs were screened for resistance to GB and RWA1. A new greenhouse seedling screening technique for the identification of BCOA resistance was tested. Seed of 96 RWA-resistant barley germplasm lines was provided to cooperators for screening to 3 international RWA biotypes. Studies of genetic control of aphid resistance: Genetic populations were developed to determine genetic diversity in 8 sources of GB resistance and 7 sources of RWA resistance. Inheritance of RWA resistance in 1 germplasm line was determined. Doubled haploid populations were screened to determine inheritance of RWA resistance in 3 sources. Over 350 lines were phenotyped in an association mapping study to identify lines with unique genes for RWA resistance. Transfer aphid resistance and other value added-traits into barely breeding lines: The hulless trait was transferred into superior dual aphid-resistant germplasm lines. Heads were selected from over 100 F2 populations, and 3,000 hulless heads were screened for RWA/GB resistance. Over 4,000 F3 were increased. Over 3,000 RWA/GB-resistant hulless F4 lines were evaluated in the field. A preliminary yield trial of 75 RWA/GB-resistant, hulless, winter barley lines was conducted. Incorporate greenbug resistance genes into sorghum breeding lines and advance breeding populations: The pedigree of breeding populations was advanced and the segregating populations were screened to monitor the transfer of greenbug resistance gene(s) to breeding lines and to select promising lines with resistance to greenbug. The selection processes are the essential steps toward the development of pure lines, resulting in new variety of greenbug-resistant sorghum. Genotyping sorghum mapping populations using SSR markers: Phenotypic evaluation of the collective offspring of the two mapping populations was conducted in greenhouse, and statistical analysis by linking the phenotypic data with the genotypic data was done, leading to the identification of a major greenbug resistance gene on chromosome 9, which will help us to identify the candidate genes responsible for host resistance by integrating these experimental data to the sorghum genome sequence database in the next step. Evaluation of sorghum germplasm to identify genetic stocks or traits potential to develop sorghum varieties as feedstock for bioethanol production: Following the previous experiments, we repeated evaluation of 687 sweet sorghum lines for those important traits, including plant height, sugar content, biomass yield, and phenology of flowering. As a result, some promising lines were selected for further characterization. Screening of wheat germplasm for resistance to multiple biotypes of RWA: Identification and purification of RWA-resistant germplasm lines were continued. Fifty lines resistant to RWA2 were identified as also being resistant to RWA1, of which 30 were highly resistant and a few less resistant to RWA1. Four additional RWA1-resistant lines are also resistant to RWA2.
1. What chromosome(s) and where on those chromosome(s) is sorghum resistance to greenbug biotype I found? Sorghum, an important cereal crop worldwide, is cultivated for both grain and forage production. Greenbug is one of the major insect pests of sorghum and can cause serious damage to sorghum plants. Greenbug biotype I is the most prevalent biotype of greenbug in the U.S. Great Plains. Scientists at the Wheat, Peanut and Other Field Crops Research Unit, Stillwater, Oklahoma, identified the gene(s) responsible for sorghum resistance to biotype I and the chromosomal location of those gene(s). A chromosome mapping experiment was conducted, and phenotypic and genotypic data for greenbug biotype I resistance was collected and analyzed. We found that two separate regions of DNA on sorghum chromosome 9 are responsible for resistance to greenbug biotype I. With these findings, the process to identify new resistant parents and develop commercial hybrids will be expedited.
2. Increased production of resistance gene linked to greenbug feeding. Host defense against insect pests such as greenbug may rely on the expression of resistance genes and/or the induction of defense pathway(s). At the Wheat, Peanut and Other Field Crops Research Unit, Stillwater, Oklahoma, a study was designed to analyze the production of thaumatin-like protein (TLP), a known resistance gene in sorghum lines, which is expressed with greenbug feeding. Results showed that the production of TLP was induced by greenbug feeding and that it was time-dependent. Studies of the action of resistance genes such as TLP in sorghum in response to greenbug attack will improve our understanding of host defense mechanisms, which will help design strategies or products for pest management in agriculture.
3. Release of eight RWA/GB-resistant winter feed barley germplasm lines. Greenbug (GB) has long been a serious pest of small grains in the Southern Plains. Russian wheat aphid (RWA), a new introduction to the US in 1986, is a devastating pest of small grains in the western US. Both aphids are a threat to small grains of the Southern Plains. Plant resistance is the best answer to reducing economic and environmental costs of insecticidal control of these aphids. These new barley germplasm lines are the first to provide breeders with combined resistance in superior performing lines that they can utilize to produce dual-aphid-resistant winter feed barley cultivars.
Mittal, S., Dahleen, L.S., Mornhinweg, D.W. 2009. Barley Germplasm STARS-9577B lacks a Russian Wheat Aphid Resistance Quantitative Trait Locus Present in STARS-9301B. Crop Science. 49:1999-2004