Phalaenopsis is the most popular potted plant worldwide. However, its long spikes often lead to increased shipping costs and risks. This study investigates the effectiveness of varying the concentration, timing, and frequency of paclobutrazol (PP333) applications on shortening the spike of Phalaenopsis Join Grace ‘TH288-4’. Also we examine on different progressive-raising temperature promoting inflorescence development for prior anthesis, and on spike-truncated treatment optimizing flowering performance. Three experimental groups were established based on different PP333 application schedules: T2, T2T3 and T7T8 group. The PP333 concentrations used were 0, 250, 500, 750, and 1000 mg·L-1, applied as foliar sprays. The shortest spikes, measured from base to first flower, were observed in the T2 group with 750 and 1000 mg·L-1; the T2T3 group treated with 500, 750, and 1000 mg·L-1 PP333; and the T7T8 group treated with 1000 mg·L-1. These treatments resulted in spike lengths of 16.7-22.2 cm, which are 54-69% shorter than the control ones. PP333 application had minimal effects on other traits except root diameter. Subsequently, four experimental groups: G20, G25, G30, and G35 group, were set up based on different final flower induction temperature. Mature plants were applied with 750 mg·L-1 PP333 by foliar spray, after four weeks moved to a cool room as 20/18℃. Until the flower stalk bore 0-3 nodes, the G25, G30 and G35 groups were transferred to 25/20℃. While the flower stalk bore 4-5 nodes, the G30 and G35 group were moved to 30/25℃. When the flower stalk bore 6-7 nodes, the G35 group was finally cultured under 35/30℃. Half of plants were randomly selected and truncated the spikes while the first flower bud was 1-1.5cm long. The spike of the G35 and G30 were truncated on the 21st week, which took only 113 and 117 days from the day started placing at a cool room. The G25 and G20 group took 124 and 138 days respectively. The days to flowering of G35 and G30 group were less than G20 at least by 45 days. However, the flower of G35 group performed unusual and were the smallest. All flowers of spike-truncated plants were bigger than the controls under different temperatures. This study establishes a PP333 treatment and a flower induction temperature protocol, offering a strategy to effectively produce single-flowered phalaenopsis.
