Tolerance to drought stress

We are currently working to generate a more holistic definition of drought tolerance using two accessions of Sorghum bicolor that vary in their pre- and post-flowering responses to drought. Biomass is often used as an indicator of drought tolerance; however, solely focusing on this trait neglects the reproductive components of cereal crops, i.e., the grain. In the process of defining drought tolerance, both vegetative traits (biomass, height, leaf greenness, and leaf temperature) and grain-related traits (yield, seed weight, seed size, and seed color) are quantified under control and drought stressed conditions to determine if there is a correlation between vegetative and reproductive drought tolerance. Given that reproductive organs are sink tissues and require a lot of carbon, we predicted that reproductive tolerance will correlate with vegetative tolerance due to the limited impacts on photosynthetic capacity that accompany the maintenance of aboveground biomass, leaf greenness, and transpiration. 

Drought stress is ephemeral, but is often experienced multiple times throughout a plant’s lifecycle. As a result, it is imperative that drought-responsive changes, at both the organismal and molecular levels, are measured throughout a growing period to further our understanding of plant responses to drought. Additionally, in response to repeated and prolonged drought exposure, two phenomena, drought stress recovery and memory, can be further explored. Stress recovery refers to the re-establishment of control level homeostasis, while stress memory results in the establishment of a new, post-stress homeostatic level. In order to identify the onset of stress recovery and/or memory, physiological and transcriptional indicators of plant health are quantified during drought and recovery phases. As drought tolerant accessions perform optimally under stress, it is predicted that stress recovery will be initiated; however, we predict that drought sensitive accessions will display signs of stress memory as a mechanism to respond more effectively to repeated drought exposure. 

In order to identify the genetic controls of drought tolerance as it relates to domestication, 170 recombinant inbred lines from a cross between Sorghum propinquum (undomesticated, weedy) and Sorghum bicolor inbred TX7000, were exposed to drought stress for fourteen days. Multiple morphological and physiological indicators of plant health were measured on control and drought stressed plants. Quantitative trait loci (QTL) mapping will be used to identify candidate genes within QTL associated with domestication-derived drought tolerance.