Physiological differences among sorghum (Sorghum bicolor L. Moench) genotypes under high temperature stress

High temperature (HT) stress affects grain yield of sorghum (Sorghum bicolor L. Moench). Understanding responses to HT stress is critical for developing HT tolerant sorghum genotypes. The objectives of this study were to understand the effects of HT stress on physiological and reproductive traits of various sorghum genotypes by quantifying oxidative damage in leaves and pollen grains. Sorghum genotypes at booting were exposed to optimum temperature (OT; 30/20 degrees C, day maximum/night minimum) or HT (38/28 degrees C) for 10 d. Photosynthetic and reproductive traits were recorded 7-d after HT stress. Results showed that HT stress decreased, quantum yield of PS II (Phi PSII), electron transport rate and transcript levels of rubisco activase; and glutathione peroxidase enzymes; and more induced cell membrane damage. HT stress decreased pollen viability, pollen germination, and seed-set. Abnormal exine ornamentation was observed in pollen grains at HT. Response of pollen to temperature varied among genotypes. Genotypes with higher ceiling temperature for pollen germination (T-max) also had a higher percentage of seed-set under HT stress. Principal component analysis suggested that genetic variability was explained by T-max for pollen germination, percentage seed set and thylakoid membrane damage under HT stress. Tolerant genotypes had relatively less oxidative damage in leaves and pollen grains than sensitive genotypes. Principal component analysis identified DK-54-00, Pioneer 84G62, SC 1047, and SC 1019 as tolerant of HT stress, and genotypes DK 28-E, SC 15, B 35, and TX 7078 as sensitive. (C) 2013 Elsevier B.V. All rights reserved.