Thermo-tolerant and thermo-sensitive characterization of selected okra genotypes at seedling stage

Twenty different okra genotypes were screened out at seedling stage under different temperature regimes (25 °C (control), 40 °C and 45 °C) to categorize them as thermo-tolerant and thermo-sensitive. On the basis of morphological, physiological, gasses exchange, enzymatic and ionic characteristics thermo-tolerant and as thermo-sensitive okra genotypes were identified. The results revealed that heat stress caused a significant reduction in morphological (root/shoot length, plant fresh/dry weight, leaf area) and physiological attributes (photosynthesis, stomatal conductance, transpiration rate) in both thermo-tolerant and thermo-sensitive okra genotypes. Whereas, thermo-tolerant genotypes showed less reduction in morphological and physiological attributes as compared to thermo-sensitive and vice versa. Antioxidant osmolytes (proline, glycine betaine) and enzyme enzymes (superoxide dismutase, peroxidase) activities in root/shoot indicated that thermo-tolerant genotypes had the highest heat tolerance potential as they showed the greater increase in antioxidant enzyme and osmolytes activities as compared to the thermo-sensitive genotypes. Ionic attributes (calcium and magnesium) were least affected in thermo-tolerant genotypes whereas this trend was opposite for thermo-sensitive okra genotypes. Overall, it was concluded that heat/ high-temperature stress is very drastic for growth and development of okra genotypes at seedling stage and based upon cluster analysis membership genotypes Kiran-51, Punjab selection, Ikra-1, Sarsabaz, Sanum, Pen beauty, Sabaz pari and Green wonder were categorized as thermo-tolerant whereas, Shehzadi, Lush green, OK-1307, Anarkali and OK-1305 were moderate-tolerant, while Ikra-3, MF-03, Okra-7100, Cick-576, Pusa sawani, Okra-3, and Ikra-2 were categorized as thermo-sensitive okra genotypes.