Effect of paclobutrazol application on growth, flowering and inulin content of ornamentalHelianthus tuberosusL.

Abstract

Paclobutrazol (PBZ) is a plant growth retardant often used in potted ornamental plants to control their height and canopy for compactness. Helianthus tuberosus L., belonging to the Asteraceae family, has the potential to be developed as an edible ornamental potted plant. It has long lasting vivid yellow flowers and contains many nutritional tubers in the underground parts. However, an obstacle for commercialization is the control of the plant height. Therefore we evaluated different PBZ application methods (media drenching and tuber soaking) and concentrations (0, 50 and 100 ppm) on growth, flowering and inulin content of H. tuberosus The results show that PBZ concentration significantly reduced all growth parameters (plant height, canopy width and total leaf area), providing more compact plants of good commercial value, representing a reduction of compactness index (cm2 cm-1) and confirming its efficiency to reduce the vertical growth. None of the PBZ application methods affected plant height, canopy width, number of flowers, percentage of flowering and inulin content, while tuber-soaking treatment gave a reduction of total leaf area and compactness index. PBZ application at 50 ppm was sufficient to reduce plant height, total leaf area and compactness index compared with normal plants. Increasing the PBZ concentration seems to increase inulin content in tubers, although it seems to decrease the number of flowers.