Flowering Time and Physiological Reaction of Dendrobium nobile Lindl in Response to TDZ Application

The objective of this work was to analyze the effect of Thidiazuron (TDZ) treatment on floral initiation, flowering time, ornamental characteristics and physiological metabolism of potted Dendrobium nobile. Three TDZ concentrations (200, 500 and 1000 mg L−1) were applied as solution to water the root zone of the plants. Control plants (plants watered with water) showed a good vegetative development but no floral branches. TDZ greatly influenced the flowering process. For all the tested TDZ concentrations, the first flower bud occurred at 55–60 days after the last irrigation (DAI), the highest TDZ concentration showing the major delay in its occurrence. The initial flowering (30% of flowered plants) began 47 days after the first flower bud initiation with no statistical differences among the treatments. Plants treated with TDZ 500–1000 mg L−1 showed the longest period of flowering (about 32 days) and the single flowers delayed the withering of about 2–3 days compared to the lowest TDZ treatment (200 mg L−1). The number of flowers, floral branches and flowering percentage were distinctly influenced by the TDZ concentration. The highest percentage of flowering (40%) was scored when plants were watered with a TDZ solution at 500 mg L−1 and this was a performant treatment providing the best morphological flower features for the ornamental value of this plant. Among the physiological factors affecting the flowering, this study showed that TDZ increased the relative membrane permeability which facilitated the transport of macromolecular flower-forming substances into and out of the membrane. Therefore, the membrane permeability change could be an indicator of shifts in physiologically active substances during the flowering transition process in Dendrobium nobile plants.