1a. Objectives (from AD-416)
The objectives of this research project are to (1) analyze aphid resistance sources from different origins to determine genetic diversity of the resistance in wheat germplasm using genetic and genomic methods, (2) conduct genotyping experiments to facilitate genetic characterization of those aphid resistant materials, (3) develop DNA markers to aid selection of breeding lines through marker-assisted selection, and (4) develop and evaluate elite breeding lines with improved resistance to greenbug and/or Russian wheat aphid. Thus, the overall goal of this specific cooperative research project will contribute to a better understanding of host resistance to cereal aphids in wheat and to the development of high-performance wheat cultivars/germplasm with enhanced genetic resistance to greenbug and Russian wheat aphid.
1b. Approach (from AD-416)
In this study, various resistance sources of wheat germplasm from different origins will be evaluated for specific reaction between host resistance and aphid virulence to determine genetic diversity of aphid resistance and to document the relatedness of these resistant sources. The initial phenotypic evaluation then will be confirmed by molecular analysis with AFLP markers. Briefly, various resistant lines will be infested with selected biotypes of greenbug or Russian wheat aphid in the controlled greenhouse environment. During infestation, phenotypic responses of the host plants will be evaluated at various time points to determine the resistance mechanisms. Then genomic DNA will be extracted from all lines and the genetic diversity and relatedness among the resistant lines will assessed with AFLP (amplified fragment length polymorphism) markers. In a parallel approach, mapping populations will be developed to identify genetic factors or loci that influence aphid resistance using SSR markers and to determine the recombination distance. DNA markers will be developed to estimate linkage relationships between aphid resistance and other related traits based on recombination events between alleles of different loci. DNA markers closely linked to the resistance traits will be identified and optimized in this study, which offers valuable tools to enhance the efficiency of wheat breeding through marker-assisted selection and to facilitate isolation of aphid resistance genes via the map-based cloning.
3. Progress Report
This study aims to characterize genetic resistance to cereal aphids in wheat and to develop molecular markers to aid the breeding process of wheat. Following genetic diversity studies in the past year, association mapping was performed on a collection of 64 wheat lines to identify candidate resistance genes to aphid feeding. This study was based on the host plant responses to RWA1, RWA2, and greenbug biotype E using 182 simple sequence repeat (SSR) markers. Both phenotyping and genotyping experiments were completed, resulting in a large amount of valuable data. Data analysis is underway to develop marker-trait correlation. This project was conducted by a post-doctoral research associate. The ADODR monitored activities through regular meetings, email and telephone communications, as well as through technical supervision of the post-doctoral research associate who worked on the project.