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TEMPERATURE AND PHOTOPERIODIC EFFECTS ON GROWTH AND FLOWERING OF ZYGOPETALUM REDVALE 'FIRE KISS' ORCHIDS

2003; International Society for Horticultural Science; Issue: 624 Linguagem: Inglês

10.17660/actahortic.2003.624.20

2406-6168

Roberto G. López, Erik S. Runkle, Royal D. Heins, Catherine M. Whitman,

Fern and Epiphyte Biology

Flowering potted orchids have become the second most valuable floriculture flowering potted crop in the United States. However, little or no quantitative information exists on the flowering process of the majority of orchid species. We performed experiments to determine how temperature and photoperiod influence leaf development and flower induction of Zygopetalum Redvale ‘Fire Kiss’. In the first experiment, plants were placed under photoperiods ranging from 10 to 24 h of continuous light or 9 h with a 4-h night interruption (NI). Sixty percent to 80% flowered when grown under every photoperiod except continual (24 h) light, and flowering was slightly hastened under photoperiods ≤14 h. In a separate experiment, plants were placed into environmental chambers with constant temperatures of 14, 17, 20, 23, 26 and 29 °C and 9-h photoperiods with or without a 4-h NI. Plants developed nodes faster as temperature increased from 14 to 26 C; after 15 weeks, plants at 14 C had developed an average of only 1.8 new nodes, while those at 26 C had developed an average of 4.8. In the third experiment, plants were placed under 9or 16-h pre-cooling photoperiods for 8 weeks, then were transferred to cooling temperatures of 11, 14, 17, 20, and 23 oC with 9and 16-h photoperiods for 8 weeks. Plants grown under a 9-h pre-cooling photoperiod and then transferred to 11 or 14 C had the highest flowering percentages and reached visible inflorescence in 17 to 22 days. Collectively, these studies indicate that Zygopetalum without a low temperature treatment is a quantitative short day plant. The most rapid, complete, and uniform flowering occurred when plants were grown under short days and then subjected to temperatures of 11 to 14 C. INTRODUCTION In the United States, potted plants are commonly purchased for holidays such as Mother’s Day, Easter, and Valentine’s Day. Thus, greenhouse growers must be able to produce flowers (either for cut flowers or as potted plants) to meet specific market dates. Plants that do not have flowers, or have flowers that are too immature (e.g., only flower buds) or mature (e.g., flowers are all open), are often not sold or sold for a low price. Potted flowering orchids are produced in vast quantities throughout the world. Orchids are the second most valuable flowering potted crop in the United States, with an estimated wholesale value of approximately $100 million (USDA, 2001). However, the flowering process of the majority of orchid species is understood poorly, or not at all. Some notable exceptions include Phalaenopsis, Cattleya, Cymbidium, and Dendrobium. In these genera, low temperatures, short photoperiods, or both, regulate the flowering process (Rotor, 1952; Sakanishi et al., 1980; Ichihashi, 1997). The Orchidaceae includes over 30,000 species, many with considerable ornamental appeal. The commercial potential of the vast majority has not yet been explored. We are in the process of screening genera that show promise for commercial production as flowering potted plants. Important production factors include showiness of flower display, ease and length of production, uniformity, compact size, and flower longevity. Zygopetalum is a South American genus of orchids that have fragrant flowers with lime-green and dark maroon flower petals and a white and magenta lip. Their exotic, Proc. XXVI IHC – Elegant Science in Floriculture Eds. Th. Blom and R. Criley Acta Hort. 624, ISHS 2003 Publication supported by Can. Int. Dev. Agency (CIDA) 156 attractive flowers and naturally compact habit (≈25to 40-cm tall) make Zygopetalum appealing flowering potted plants. However, control of growth and flowering is not well understood, and to our knowledge, no scientific studies on flower induction have been published on this genus. We have performed experiments to determine how temperature and light controls growth and development of Zygopetalum Redvale ‘Fire Kiss’. Specifically, our objectives were to determine: 1) how temperature influenced the rate of plant growth; 2) if a period of cool temperatures influenced flowering; 3) if photoperiod alone controlled flowering; and 4) if photoperiod before and during cooling influenced flowering. Here, we present preliminary results after one year of experiments. MATERIALS AND METHODS Plant Material In June 1999, Zygopetalum Redvale ‘Fire Kiss’ plants were received and grown in vitro by a commercial greenhouse (California, U.S.), transplanted into 38-cell plug trays in June 2000, and into 10-cm pots in April 2001. In California, plants were grown at 16 to 26 °C under natural photoperiods (lat. 37N) with a maximum photosynthetic photon flux (PPF) of 300 μmol·m·s. Five hundred plants in 10-cm pots in a bark and perlitebased media were received in East Lansing, Michigan, USA on 6 May 2001. All plants were maintained at 23 °C in a glass-glazed greenhouse until experiments began. The photoperiod was a constant 16 h, consisting of natural daylengths (lat. 42oN) with dayextension lighting from high-pressure sodium (HPS) lamps, which delivered a supplemental PPF of ≈50 μmol·m·s at plant height [as measured with a LI-COR quantum sensor (model LI-189; LI-COR, Inc., Lincoln, Nebr.)]. Each plant had at least one mature and two immature pseudobulbs at the onset of experiments. Photoperiod Treatments (Expt. 1) On 31 May 2001, ten plants were placed under each of seven photoperiods: 10, 12, 13, 14, 16 or 24 h of continuous light or 9 h with a 4-h (2200 to 0200 HR) night interruption (NI). Continuous photoperiods consisted of 9-h days completed by day extension lighting; lamps were turned on at 1700 HR and turned off after each photoperiod was completed. Day-extension and NI lighting (≈3 μmol·m·s at canopy level) was provided by incandescent lamps. Plants were grown in a glass greenhouse with a constant temperature setpoint of 20 C. Opaque black cloth was pulled at 1700 HR and opened at 0800 HR everyday on all benches so plants received a similar daily light integral. From 0800 to 1700 HR, HPS lamps provided a supplemental PPF of ≈25 μmol·m·s at plant level when the ambient greenhouse PPF was less than 400 μmol·m·s. To provide uniform night temperatures of 20 °C, a data logger controlled a 1500-W electric heater, which provided supplemental heat under each bench as needed. Temperature and Photoperiod Treatments – Environmental Chamber (Expt. 2) Ten plants were assigned randomly to walk-in controlled-environment chambers on 12 June 2001 with constant temperature setpoints of 14, 17, 20, 23, 26, and 29 oC. Each chamber was divided in half with black plastic and two photoperiods were created: 9-h of light without or with NI lighting (≈3 μmol·m·s from 2200 to 0200 HR) from incandescent lamps. The 9-h base photoperiod was provided by a combination of coolwhite fluorescent (VHOF96T12, Philips, Bloomfield, NJ.) and incandescent lamps from 0800 to 1700 HR at 150 μmol·m·s. Plants were grown for 20 weeks, except for those at 29 oC, in which observations were terminated after 13 weeks due to declining growth and plant mortality. The average daily air temperature recorded in the chambers was 13.4, 16.7, 19.5, 22.4, 25.5, and 28.6 C. At the beginning of the experiment, one immature pseudobulb was identified and node development was recorded weekly by counting the number of leaves from the soil level to the terminal end of the shoot.