Effect of growth regulator paclobutrazol on size fitting of basil as a potted plant

Abstract Basil (Ocimum basilicum L., Lamiaceae) is an herbal species cultivated primarily for culinary and aromatherapy. Basil plant height could reach more than 60 cm, and the plants tend to elongate, particularly in low-light environments. Our current study examined the potential uses of plant growth retardant paclobutrazol to control sweet basil height and improve potted basil’s ornamental quality. The treatment tested was paclobutrazol concentration at 0, 5, 10, and 20 ppm, applied as 100 mL media drenching per pot five weeks after planting. The control plants were water-drenched using the same volume at the same time. Basil treated with PBZ at 10 ppm or 20 ppm had significantly shorter, smaller shoot canopy diameter, node and leaf number than the control, but had a similar number of branches to the control. Basil treated with PBZ at 10 ppm or 20 ppm showed a more compact and bushy pot plants with the height to pot ratio of 1.5. Higher leaf chlorophyll, indicated by a higher index value, was recorded only with the PBZ concentration of 20 ppm compared to the control and the other PBZ concentrations. Basil growth responses to PBZ at 10 ppm were not significantly different from those treated with PBZ at 20 ppm, therefore the use of PBZ at a lower concentration (10 ppm) is preferable. Further studies should examine whether repeated PBZ applications at lower concentration is more effective in producing shorter and more compact pot plants.