|Authors: ||Q. Meng, E.S. Runkle|
|Keywords: ||blue radiation, far-red radiation, floriculture crops, LEDs, red radiation|
Under natural short days (SDs), low-intensity lighting during the middle of a night (night interruption, NI) can control flowering of daylength-sensitive ornamentals.
Red (R, 600-700 nm) and far-red (FR, 700-800 nm) radiation is primarily absorbed by phytochromes that mediate flowering, whereas blue (B, 400-500 nm) radiation typically has less photoperiodic relevance, at least at a low intensity.
White (W) light-emitting diodes (LEDs) emit photons over a broad spectrum; however to our knowledge, their efficacy at regulating flowering has not been published.
We investigated whether white LEDs controlled flowering of five long-day plants [calibrachoa (Calibrachoa × hybrida), coreopsis (Coreopsis grandiflora), petunia (Petunia × hybrida), rudbeckia (Rudbeckia hirta), and snapdragon (Antirrhinum majus)] and two SD plants [chrysanthemum (Chrysanthemum × morifolium) and marigold (Tagetes erecta)]. Plants were grown in a greenhouse at 20°C under 9-h SDs with or without 4-h NIs from R, B+R, cool-W, warm-W, or R+W+FR LEDs.
Irradiance at plant canopy was adjusted to approximately 2 µmol m-2 s-1 between 400 and 800 nm.
Compared with SD, all NIs similarly promoted flowering of calibrachoa and rudbeckia; however, only R+W+FR promoted flowering of snapdragon.
NIs without FR radiation (i.e., R, B+R, cool-W, and warm-W) accelerated flowering of coreopsis and petunia, but flowering under R+W+FR was 11-16% earlier than under the other NIs.
R+W+FR was less effective than the other NIs at inhibiting flowering of chrysanthemum and marigold.
Cool-W and warm-W had similar effects on flowering and development of all crops.
Plant height of calibrachoa, coreopsis, and marigold at flowering was greatest under R+W+FR; however, stem length of the other crops was similar under all NIs.
We conclude that W LEDs inhibited flowering of SD plants and were as effective as R or R+W+FR radiation at promoting flowering of some, but not all, long-day plants.
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