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. Specifically, germplasm collections will be mined for traits that will extend the growing season and enhance yield and biomass production. The genetic bases of cold and heat tolerance will be elucidated initially via genetic mapping of these traits from a new mapping population synthesized specifically for this purpose. 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:
In FY2011-2012, scientists in Lubbock, Texas, successfully completed the characterization of a new mapping population BTx623 by PI567946 for early season cold tolerance. Twenty recombinant inbred lines from the population were selected based on controlled and field cold tolerance. The 20 inbred lines were used to make hybrids for cold tolerance testing. Many new cold-tolerant and drought-tolerant (stay-green) lines have been identified from the Ethiopia sorghum germplasm collections. A new sorghum breeder has joined the research team while working his master's degree, and he has made significant progress toward crossing the cold-tolerant and drought-tolerant lines to standard U.S. male sterile (A), maintainer line (B), and restorer line (R) for making hybrids.
1. A quantitative method to determine post-flower drought tolerance was developed. Quantitative method to determine post-flower drought tolerance developed. Scientists at the Plant Stress and Germplasm Development Unit at Lubbock, Texas, developed a method that can quantify the degree of post-flower drought tolerance, commonly known as 'stay-green' trait. The stay-green trait, the ability of a sorghum plant to remain green following a post-flower drought event, is an important trait linked to increased sorghum grain yield and yield stability under drought conditions. It is also a trait that is very difficult to determine under field conditions because it needs a particular intensity of drought stress at a particular developmental stage. From the traces of High Performance Liquid Chromatograph (HPLC) of leaf extract, the scientists observed an unknown peak that is present in high levels across all lines with stay-green trait, and low or absence in lines without the stay-green trait (senescent lines). The unknown compound was identified as dhurrin, a cyanogenic glucoside that is known as an insect repellent and a nitrogen reserve during stresses. Subsequently, the content of dhurrin was found to be quantitatively associated with levels of stay-green. This discovery will enable the scientists to identify the level of 'stay-green' for post-flower drought tolerance.