EFFECTS OF EMERGING SHOOT SIZE, TEMPERATURE, AND BENZYLADENINE ON GROWTH AND FLOWERING OF ZYGOPETALUM REDVALE 'FIRE KISS'

Abstract

Zygopetalum is an epiphytic and terrestrial orchid genus that originates from mountainous regions of South America and has exotic, fragrant flowers. We performed experiments to determine how emerging shoot length, temperature, and application of benzyladenine (BA) influence growth and flowering of Zygopetalum Redvale 'Fire Kiss'. In the first experiment, the length of one immature vegetative shoot was measured on each 4-year-old plant at week 0 and plants were assigned to groups based on emerging shoot length: 1.0 to 2.0 cm, 3.0 to 4.0 cm, 6.0 to 7.0 cm, or 9.0 to 10.0 cm. Plants were transferred to environmental chambers with constant temperatures of 12.5, 15.0, 20.0, or 25.0°C and a 9-h photoperiod and grown for 8 weeks. Plants were then grown in a greenhouse at a constant temperature of 23°C with a 16-h photoperiod. After 73 days, 63 or 75% of plants had developed a visible inflorescence (VI) if emerging shoots between 3.0 and 7.0 cm in length were exposed to 12.5 or 15.0°C. No plants developed a VI when grown at 20 or 25°C, regardless of shoot length. In the second experiment, vegetative 5.5-year-old plants were grown in a greenhouse with a constant temperature of 14 or 20°C and a 16-h photoperiod. Plants received a foliar spray application (volume of 0.2 L·m -2 ) of BA at 200 or 400 mg/L at weeks 0 and 4 or weeks 4 and 8. Control plants did not receive a BA application. At week 8, plants were transferred to a greenhouse at a constant temperature of 20°C with a 16-h photoperiod. After 4 weeks, plants that were treated with BA had developed a mean of 7.2 to 10.7 new immature shoots per plant, while untreated plants had only 0.4 to 0.8 new shoots. Thus, application of BA could be used to stimulate shoot development to increase vegetative growth of Zygopetalum.