Maintenance of Tissue Water Status, Osmoregulation, and Antioxidant Defence System Improves Heat Tolerance in Okra Genotypes with Contrast Heat Tolerance

Climate-change-driven global warming is posing a serious threat to the productivity of vegetable and field crops — more so in summer crops. Okra (Abelmoschus esculentus L. Moench) is one of the leading summer vegetables; however, this is often exposed to an extremely high temperature causing significantly detrimental effects on its growth and yield. This experiment was conducted to investigate the growth, morphological, physiological, and enzymatic responses of okra genotypes to heat stress. Four okra genotypes, Sabaz pari and Green wonder (heat tolerant) and Click-5769 and MF-03 (heat sensitive), were grown under optimal (25 °C) and heat stress (45 °C) conditions. Heat stress caused a significant reduction in plant-water status, rate of photosynthesis, plant biomass, and fruits. However, the extent of reduction was more in the genotypes Click-5769 and MF-03 than the genotypes Sabaz pari and Green wonder. Heat stress caused a 38.69% reduction in the number of fruits/plant in the genotype whereas the highest reduction in fruit weight/plant (38.29%) was noted in the genotype Click-5769. However, heat stress caused only a 25.79% reduction in fruit weight/plant in the genotype. The genotypes Sabaz pari and Green wonder had more accumulation of proline and glycinebetaine and had a higher level of activities of antioxidant enzymes (peroxidase, superoxide dismutase, ascorbate peroxidase, and guaiacol peroxidase) than the genotypes Click-5769 and MF-03 under heat stress. The genotypes Sabaz pari and Green wonder had better growth and fruit yield, under heat stress, than the genotypes Click-5769 and MF-03 owing to the maintenance of tissue water status, accumulation of osmoprotectants at a higher level, activation of the antioxidant defence system, and continuation of photosynthesis. These genotypes can be used in breeding programs aimed to develop heat-tolerant okra genotypes.