Abstract: The amount of epicuticular leaf wax has been associated with plant adaptation to water stress. Prolonged low soil moisture confers greater wax accumulation. Epicuticular leaf wax has also been found to correlate positively with leaf reflectance and temperature depression. Growing sorghum adapted to dry conditions, yet productive, offers great promise to future food, feed and energy security in developing regions of the world. Knowledge of a single variety response to varying water supply conditions would improve selection of yield stability traits. For meaningful assessment, this study focused on determining the genetic overlap between the regulation of the staygreen trait in sorghum, canopy temperature depression (CTD) using differential infrared thermometer, and total and compositional epicuticular wax content in a recombinant inbred line population derived from BTx642 and RTx7000. The RIL population and wax was determined from individual lines grown at three locations. Plants were grown in the greenhouse, and in two field locations under irrigation in one location and rain fed in another. Samples were taken from three flag leaves per RIL at flowering for each location. The canopy temperature depression of seven individual plants per RIL was also recorded at each location. QTL mapping was used to determine the overlap between, leaf wax, CTD and staygreen.

Keywords: Sorghum bicolor, water stress, staygreen, epicuticular wax, canopy temperature depression.