Posted on Dec 01, 2010
Post-flowering drought tolerance (the “stay-green” trait) is an essential trait for increasing the production of sorghum [Sorghum bicolor (L.) Moench] in increasingly variable climates. Previously, methodologies for identifying the nonsenescent (stay-green) trait required the right intensity of drought stress at the right developmental stage to visually evaluate lines in the field. Field-based evaluations of drought tolerance are notoriously difficult to manage, and often require growing lines in multiple locations across several years in order to acquire a meaningful assessment of the stay-green trait. Now, because of a new technique developed in my laboratory, we can readily identify stay-green lines by means of a 30-minute high temperature challenge to leaf tissue from pre-flowering well-watered sorghum and 30-minute room temperature recovery. Evaluation of ten known stay-green and senescent sorghum lines with this bioassay allowed us to separate the two classes of sorghum from well-watered pre-flowering plants. The stay-green lines can also be separated from senescent lines under well-watered greenhouse conditions from the boot-stage onward. This technology will greatly reduce the selection time needed to identify drought tolerant sorghum.
The proposed research will continue to use this new technology in a two pronged research approach to identify germplasm with improved drought tolerance. The first approach was to evaluate photoperiod sensitive lines of the Sudan Core Collection (Dahlberg et al., 2004) from the USDA sorghum collection for lines with the “stay-green signature” provided by this technique. Lines with Stay-green and non-stay green characteristics in the bioassay were identified. These lines will be re-evaluated in the coming year to ensure a reproducible phenotype. Lines from the Ethiopian sorghum collection will be evaluated in the coming year for the stay-green trait.. The second approach was to characterize mutants of BTx623 that we have isolated and identified as exhibiting the “stay-green signature” under field and greenhouse conditions. Existing mutants were confirmed and back-crossing initiated. Additional putative mutants were identified from a field screen and will be evaluated to ensure that a reproducible phenotype is observed. Both research avenues are providing new sources of drought tolerance that can be used to improve sorghum hybrids. Mutants of BTx623 that exhibit the stay-green trait can be moved directly into breeding programs to provide new more drought tolerant sorghum hybrids. Lines identified from the screening of the photoperiod sensitive lines can be moved into the sorghum conversion program to develop photoperiod insensitive lines, or used directly in tropical environments to move the stay-green trait into elite germplasm.