Optimizing Paclobutrazol Application Dose and Timing Improve Seedling Quality and Plant Productivity in Pepper (Capsicum annuum L.) in Open Field

Paclobutrazol (PBZ) is a plant growth retardant used to regulate plant architecture and might improve seedlings quality and plant productivity. This study evaluated the effects of PBZ concentration and application timing on seedling growth, physiological and biochemical responses, anatomy, and subsequent field productivity of pepper (Capsicum annuum L.). A commercial pepper cultivar was treated with PBZ at 0, 15, 30, and 60 mg L⁻¹ at the first, second, or third true-leaf stage during two growing seasons (2022 and 2023). Application of the PBZ significantly reduced seedling height while increasing stem diameter and SPAD values at seedling stage. In contrast, shoot dry weight decreased from 0.35 and 0.33 g in controls (untreated plants) to 0.26 and 0.27 g under 30 mg L⁻¹ PBZ. In addition, PBZ application enhanced antioxidant activity, particularly peroxidase, which increased from 0.057 in untreated seedlings to 1.69, 1.92, and 1.95 at 15, 30, and 60 mg L⁻¹, respectively. Anatomically, PBZ increased leaf lamina thickness and vascular tissue development in leaves and stems. Interestingly, PBZ increased chlorophyll content, leaf and branch numbers, biomass, and fruit yield, but increasing PBZ above 30 mg L⁻¹ provided limited additional benefit and tended to reduce yield at 60 mg L⁻¹. Overall, optimizing PBZ application (concentration and timing) might provide better seedling quality and subsequent field and yield performance in pepper.