Plant growth regulators are known to improve plant’s vegetative growth and yield when applied at very low concentrations. Ascorbic acid (Vitamin-C) plays a vital role in sustaining plant growth among the numerous plant growth regulators that control growth under normal or stress conditions. An experiment was conducted during rabi 2018-19 to assess the performance of black cumin crop when sprayed with different ascorbic acid concentrations, with the objective of digging out the best ascorbic acid concentration for enhancing the production of black cumin under climatic conditions of Haripur. The results showed that 100 µM ascorbic acid was found to be effective followed by 150µM ascorbic acid. Photosynthetic rate (m mol (CO₂) m^-2 s^-1), Stomatal conductance (mmol H₂O m^-2 s^-1), Net CO₂ assimilation rate (μmol CO₂ m^‐2 s^‐1), Transpiration rate (mmol H₂O m^-1 s^-1), Peroxidase (POX), Plant height, number of capsules plant^-1, seeds capsule^-1, 1000-seed weight (g) and Seed yield (kg ha^-1) were significantly affected from ascorbic acid concentrations. However, as this study was conducted with only with ascorbic acid, it is advisable to conduct an experiment with various other growth regulators, their combinations and different concentrations to check out their synergistic effects on production traits of black cumin to make reliable and acceptable recommendations.

Keywords: Black cumin, Photosynthesis, antioxidant enzymes, growth regulator, ascorbic acid