Investigation of morphophysiological characteristics of cultivars and promising lines of grain sorghum [Sorghum bicolor (L.) Moench] under late season drought stress

This study aimed to investigate some physiological mechanisms of drought tolerance in grain sorghum genotypes.

The experiment was conducted as a split plots design based on a randomized complete block design with three replications at Karaj. Irrigation regime as the main factor in three levels, including normal irrigation , mild stress, and severe stress and genotype as the sub-factor at five levels were evaluated.

Drought stress decreased biological yield, grain yield, chlorophyll content, stomatal conductivity, and osmotic potential and increased the canopy temperature, proline, and soluble sugars. Under normal irrigation, the highest grain yield (8994 kgha-1) was obtained by cultivar Kimia. In contrast, the maximum grain yield under mild and severe stress conditions (7633 and 6275 kgha-1) was recorded in cultivar Fouman. Also, under stress conditions, cultivar Fouman showed the highest stomatal conductivity and the lowest percentage of yield reduction compared to normal irrigation. In addition, the lowest canopy temperature was recorded in Fouman cultivar under mild and severe stress conditions(32.40 and 32.63 °C, respectively).

Overall, cultivar Fooman with higher water uptake efficiency than other genotypes, which showed more stomatal conductivity and lower canopy temperature, was able to reduce the severity of water deficit stress in the plant and produce maximum grain yield under drought stress. Cultivar Kimia was able to increase its water absorption capacity and produce a relatively good yield under stress conditions by reducing the osmotic potential and increasing the accumulation of osmolytes such as soluble sugars and proline.