Determination of critical level of brassinosteroid (24-epibrassinoloid) for heat-tolerance in okra (Abelmoschus esculentus L.)

This study aimed at determining suitable dose of 24-epibrassinoloid (24-ebl) for improving morphological,physiological,and photochemical efficiency of ps ii (fv/fm) characteristics in thermo-tolerant (sabaz pari and green wonder) and thermo-sensitive (mf-03 and click-5769) genotypes of okra (abelmoschus esculentus l.). the study was performed in a growth chamber at 40 °c by applying different levels of 24-ebl (i.e.,0 µm (control treatment),0.25 µm,0.50 µm,0.75 µm,1.00 µm,1.25 µm and 1.50 µm). foliar application of 24-ebl improved root and shoot growth,plant fresh and dry weight,leaf area,photosynthesis rate,chlorophyll content and photochemical efficiency of ps ii in thermo-tolerant as well as of thermo-sensitive okra cultivars as compared to control plants. however,increase in the above stated characteristics was greater in thermo-tolerant okra genotypes as compared to thermos-sensitive genotypes,at all tested levels of 24-ebl. greater reduction in electrolyte leakage in both thermo-sensitive and thermo-tolerant okra genotypes was observed with 1.50 µm 24-ebl. considering increase in plant growth and biomass,leaf area,chlorophyll content,photosynthesis rate,photochemical efficiency of ps ii and reduction in electrolyte leakage,both in thermos-tolerant and thermo-sensitive okra genotypes,it was concluded that 1.50 µm 24-ebl was the most suited level of brassinosteroid to improve the thermo-tolerance potential of okra genotypes. © pakistan academy of sciences.