|Authors: ||M.G. Blanchard, E.S. Runkle|
|Keywords: ||bedding plants, herbaceous perennials, night interruption, photoperiodic lighting |
Photoperiod is often manipulated during commercial production of many floriculture crops to induce or prevent flowering in photoperiodic sensitive species.
To promote flowering in long-day plants, continuous 4-h night-interruption (NI) lighting at a low-intensity or cyclic lighting (e.g., 6 min on and 24 min off) for 4h during the middle of the dark period is generally effective.
A new technology for greenhouse long-day lighting was developed commercially using a stationary high-pressure sodium (HPS) lamp with an oscillating parabolic reflector (cyclic HPS lamp). The reflector provides an intermittent beam of light over a relatively large growing area.
We performed an experiment to compare the efficacy of a cyclic HPS lamp on flower induction in long-day floriculture crops with traditional NI lighting strategies. Asclepias tuberosa, Campanula carpatica ‘Pearl Deep Blue’, Coreopsis grandiflora ‘Early Sunrise’, Petunia ‘Easy Wave Coral Reef’, and Rudbeckia hirta ‘Becky Cinnamon Bicolor’ were grown in a glass-glazed greenhouse at a constant temperature of 20°C with natural short-day photoperiods and NI treatments.
NI lighting was delivered during the middle of the dark period (10pm to 2am) from a 400-W cyclic HPS lamp mounted at one gable end of the greenhouse or from incandescent (INC) lamps that were illuminated for the entire 4h or for 6 min every 30 min for 4h.
Plants under cyclic HPS were grown at lateral distances of 1, 3, 7, 10, or 13 m from the lamp.
Control plants were grown under a constant 9-h photoperiod.
After 35 days, the reflector on the cyclic HPS lamp malfunctioned and stopped oscillating, although the lamp continued to turn on during the NI. Therefore, the results of this experiment are considered preliminary.
As the lateral distance from the cyclic HPS lamp increased from 1 to 13 m, the maximum photosynthetic photon flux decreased exponentially from 20.9 to 0.4 µmol∙m–2∙s–1. After 11 weeks, 100% of all species except Asclepias and Coreopsis had a visible flower bud (VB) under cyclic HPS or INC lamps.
In Campanula, Petunia, and Rudbeckia, flowering was delayed by 7 to 12 days when the INC lamps operated cyclically compared to being operated during the entire 4h of the NI treatment.
These results indicate that a cyclic HPS lamp can be used for NI lighting to induce flowering in these long-day species.
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