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 identify mechanisms and/or genes that play important roles in host resistance against aphids. The characteristic brown coloration in midrib (bmr) of sorghum plants is associated with reduced lignin content and altered lignin composition. The traits are beneficial, as they contribute to improved forage digestibility for animals and efficient conversion from lignocellulosic biomass to bioethanol, but may have negative impacts on fitness and defense of crop plants. In the current year, the research effort was focused on genetic analysis of a mapping population developed from the cross between the elite sorghum line BTx623 and a mutant line (brown midrib, bmr). This population was grown out as 200 individuals in the F2 generation, and phenotypic evaluation was conducted. Also, progress of genotyping all individuals using SSR markers is underway in the lab.