Differential Response of Sorghum Genotypes to High Temperature Stress Is Mediated Through Oxidative Damage in Leaves and Pollen Grains.

Sorghum (Sorghum bicolor L. Moench) grain yield is severely affected by high temperature (HT) stress during flowering stages by affecting various physiological processes. Improved understanding of such responses is critical for developing HT tolerant genotypes. The objectives of this study were to understand the effects of HT stress on (i) leaf physiological and (ii) reproductive processes by quantifying oxidative damage in leaves and pollen grains. Sorghum genotypes are exposed to optimum temperature (OT; 30/20ºC, day maximum: night minimum) or HT (38/28ºC) for 10 d during booting stage. The various photosynthetic and reproductive traits were recorded on 7-d after HT stress. Results showed that HT stress decreased photosynthetic rate through increased reactive oxygen species (ROS) production, cell membrane damage, mesophyll and bundle sheath damage, and decreased quantum yield of PS II, electron transport rate and transcript levels of rubisco activase, EF-Tu, ascorbate peroxidase and glutathione peroxidase enzymes. The pollen viability, pollen germination and seed-set were decreased by HT stress through tapetum cell damage, increased ROS production and membrane damage. Genotypes with higher ceiling temperature for pollen germination (T_max) had higher seed-set percent. The tolerant genotypes had lesser oxidative damage in leaves and pollen grains than sensitive genotypes. The principal component analysis identified DK-54-00, Pioneer 84G62, SC 1047 and SC 1019 as tolerant and DK 28-E, SC 15, B 35 and TX 7078 as sensitive to HT stress. HT stress tolerant genotype can be developed through altering antioxidant defense system in leaves and pollen grains.