1a. Objectives (from AD-416)
The objective of this project is to develop an improved understanding of the physiological, molecular, and genetic basis of abiotic stress tolerance in sorghum in order to increase the productivity and nutritional quality of sorghum. Over the next 5 years we will focus on the following specific objectives: Objective 1: Develop and utilize new screening tools to identify and create novel sources of drought tolerance in sorghum. Objective 2: Identify quantitative trait loci (QTLs) contributing to abiotic stress tolerance and implement molecular marker-assisted selection for sorghum improvement. Objective 3: Identify physiological traits associated with abiotic stress tolerance in superior germplasm and improved breeding materials. Objective 4: Enhance pre-flowering and post-flowering drought tolerance in sorghum by characterizing physiological drought stress responses throughout plant development, genetic mapping of these traits, identifying photoperiod-sensitive sorghum lines with post-flowering drought tolerance, and combining photo-period sensitivity and post-flowering drought tolerance in one sorghum genotype or line.
1b. Approach (from AD-416)
A comprehensive approach integrating Plant Physiology, Genetic Mapping, and Plant Breeding will be used to study the mechanisms of abiotic stress tolerance in sorghum and to develop superior germplasm with enhanced abiotic stress tolerance.
3. Progress Report
Subobjective 2C was suspended due to the loss of a scientist to private industry. We plan to re-start this subobjective once the position is refilled. A method to screen staygreen trait was tested in the field with known standard lines. The method has been applied to screen the Sudan collection of sorghum germplasm for new genetic sources of post-flowering drought tolerance. All other milestones are fully or substantially met.
1. A reliable way to screen post-flowering drought tolerance in sorghum established: Post-flowering drought tolerance, known as "staygreen", is an important trait for yield increase and stability of sorghum under limited- or no-irrigation conditions. Conventional methods to evaluate this trait under field conditions is complex and expensive because multiple year and multiple location studies are required due to the strong interactions of this trait with environment. Scientists from the Plant Stress and Germplasm Development Unit at Lubbock, Texas, have developed a method to evaluate the staygreen trait based on chlorophyll fluorescence in sorghum grown under well-watered conditions. The method has been validated under field conditions with standard lines with known responses of the staygreen trait. The method is currently used to screen a large collection of sorghum germplasm from Sudan for the staygreen trait to expand the genetic bases of post-flowering drought tolerance.
2. New recombinant population for mapping cold tolerance in sorghum: There is an increasing demand for improving cold tolerance in sorghum. Scientists from the Plant Stress and Germplasm Development Unit at Lubbock, Texas, have developed a recombinant inbred mapping population derived from a cross between an elite US inbred line RTx430 and a cold-tolerant Chinese line PI610727. The entire population consisting of 174 inbred lines at F7 generation were released and deposited into the National Germplasm Resource Information Network (GRIN). This population is being used to identify genes responsible for cold tolerance in sorghum.
3. Genome-wide DNA marker released: Robust and evenly distributed DNA markers are needed for mapping agronomic traits and molecular breeding in sorghum. Scientists from the Plant Stress and Germplasm Development Unit at Lubbock, Texas, annotated and validated 471 DNA markers evenly distributed across sorghum genome. The collection of markers was names SEAMS for Sequence Anchored Microsatellites of Sorghum. The information for these DNA markers and the chromosome location in the sorghum genome are available at: http://www.lbk.ars.usda.gov/psgd/sorghum/2009SorghumSEAMs_LBKARS.xls and http://www.lbk.ars.usda.gov/psgd/sorghum/Seamschromplacement.ppt. These markers can be used to fine map genes for sorghum improvement.
4. Sorghum Diversity Panel released: Association mapping, first developed in human genetic studies to identify DNA markers or genes closely associated with specific diseases through population analysis, has become a powerful approach in plants to map quantitative trait loci (QTLs) for agronomic traits. Association mapping requires a collection of genetically diverse lines. The sorghum community has assembled a diversity panel consisting of 387 lines. Scientists from the Plant Stress and Germplasm Development Unit at Lubbock, Texas, have propagated and collected a basic observation for these lines. The diversity panel has deposited to GRIN and is now available to all scientists in the US.
5. A pedigreed sorghum mutant library online: Sorghum mutant populations are needed to characterize the function of genes within the sorghum genome. Scientists from the Plant Stress and Germplasm Development Unit at Lubbock, Texas, have developed an Annotated Individually-pedigreed Mutagenized Sorghum (AIMS) library. The mutant library possesses many interesting traits for sorghum improvement and genomic studies. The library is available online (http://www.lbk.ars.usda.gov/psgd/index-sorghum.aspx). This mutant population provides a new genetic resource for the sorghum research community.
Xin, Z., Wang, M.L., Barkley, N.L., Burow, G., Franks, C., Pederson, G., Burke, J. 2008. Applying genotyping (TILLING) and phenotyping analyses to elucidate gene function in a chemically induced sorghum mutant population. Biomed Central (BMC) Plant Biology. 8:article 103.