1a. Objectives (from AD-416)
The objectives of this research project are to analyze genetic factors that control expression of resistance in wheat, barley, and sorghum to greenbug and/or RWA and to compare the defensive response of the host plants. It is expected that this research will generate useful information to help identify genetic components responsible for aphid resistance, revealing the similarities of resistance mechanisms as well as diversity of host defense between the cereal species barley, sorghum, and wheat. Identification of the conserved resistance mechanisms will facilitate map-based gene isolation by using DNA marker information from syntenic intervals across cereal species. On the other hand, the diversity of host defense against cereal aphids can be used to develop crop plants with more durable resistance.
1b. Approach (from AD-416)
In this study, three cereal species (barley, sorghum, and wheat) will be analyzed in parallel. They will be infested with selected biotypes of greenbug or Russian wheat aphid in the controlled greenhouse environment. Following infestation, phenotypic responses of the host plants will be evaluated at various time points. Then leaf tissues of infested plants will be collected to analyze any related changes in gene expression caused by aphid infestation. DNA markers will be used to identify resistance QTLs and to localize genes for host plant resistance to the cereal aphids based on genotyping in the mapping populations. Finally we will analyze their genetic diversity in host defense and their linkage to genetically characterized resistance genes. The results from comparative genomics studies in barley, sorghum, and wheat will reveal the similarities of host resistance mechanisms and suggest possible mechanisms to generate diversity in resistance loci.
3. Progress Report
This study aims to analyze genetic components conferring resistance to greenbug and/or Russian wheat aphid and to compare the defensive responses among wheat, barley, and sorghum. In a preliminary mapping study, 370 progeny from a biparental cross between an elite sorghum line and a greenbug-resistant germplasm line were genotyped with more than 100 SSR markers. So far, both genotyping and phenotyping experiments are almost completed. Our current efforts focus on data analysis to identify molecular markers that link to the genes or the chromosomal regions responsible for resistance to greenbug in sorghum. The ADODR monitored activities through regular meetings, email and telephone communications as well as through technical supervision of a graduate student (a Ph.D. candidate) who is assigned to the project.