Leaf Dhurrin Content is a Quantitative Measure of the Level of Pre- and Postflowering Drought Tolerance in Sorghum

The presence of pre�耀owering or post�耀ower ing drought tolerance has been described in sorghum [Sorghum bicolor (L.) Moench]. Sorghum lines with pre�耀owering drought tolerance tend to senesce under post�耀owering drought stress while sorghum lines with post�耀owering drought tolerance (the stay-green trait) tend to be sensitive to pre�耀owering drought stress. Assessments of these phenotypes have been dependent on the incidence of drought stress conditions at speci�耀c developmental stages to achieve meaningful evaluation. Therefore, �耀eldbased evaluations, most of which are visual, are notoriously dif�耀cult to perform and require growing lines in multiple locations across several years to achieve ef�耀cient selection for these traits. Here we report and demonstrate a correlation between leaf dhurrin [(S)-p-hydroxymandelonitrile-C-D-glucopyranoside] contents and the level of stay-green based on leaf and plant death ratings during post�耀owering drought stresses. Post�耀owering drought-tolerant staygreen sorghums had elevated dhurrin contents while pre�耀owering drought-tolerant sorghum lines exhibited lower dhurrin contents. Lines with intermediate leaf and plant death ratings exhibited intermediate dhurrin levels. Finally, dhurrin levels determined before �耀owering from sorghum grown under irrigated or dryland conditions were related to the degree of pre- or post�耀owering drought tolerance.