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:
During the current year, our cooperative efforts focused on conducting field evaluation of the newly developed wheat breeding lines. Those lines were also screened for their reactions to infestation by virulent greenbug biotype E in greenhouse. Plants were evaluated for their response to greenbug feeding at 14 and 17 days after infestation, and damage levels were scored at those time points. In addition, 31 wheat lines were screened for resistance to Russian wheat aphid biotype 2 (RWA2). According to the damage scores assessed at days 14 and 17 following infestation, 6 lines showed as resistance to RWA2.