Journal
HORTSCIENCE
Volume 54, Issue 2, Pages 323-327Publisher
AMER SOC HORTICULTURAL SCIENCE
DOI: 10.21273/HORTSCI13630-18
Keywords
Euphorbia pulcherrima; LEDs; light quality; photomorphogenesis; photoperiod; phytochrome
Categories
Funding
- U.S. Department of Agriculture (USDA)-Agricultural Research Service Floriculture and Nursery Research Initiative
- Philips Lighting
- USDA National Institute of Food and Agriculture, Hatch project [192266]
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Manipulating light quality is a potential alternative method of regulating plant height in the commercial production of ornamental crops. In particular, end-of-day (EOD) lighting with a high red (R; 600-700 nm) to far-red (FR; 700-800 nm) ratio (R: FR) can suppress extension growth, whereas a low R: FR can promote it. We investigated the effects of the R: FR and duration of EOD lighting in regulating extension growth and flowering of two poinsettia cultivars, White Glitter and Marble Star. Plants were grown at 20 8C under 9-hour days with or without EOD lighting provided by two types of lightemitting diode bulbs: R+ white+ FR (subsequently referred to as R+ FR) and FR only. The R: FR ratios were 0.73 and 0.04, respectively, and the photon flux density between 400 and 800 nm was adjusted to 2 to 3 mmol.mL2.s-1 at plant canopy. The six EOD lighting treatments were R+ FR or FR for 2 or 4 hours, 2 hours ofR+ FR followed by 2 hours of FR, and 4 hours of R+ FR followed by 2 hours of FR. We also investigated the impact of a 4hour moderate-intensity (13 mmol.mL2.s-1) EOD FR treatment in the second replication. EOD lighting generally increased poinsettia extension growth, with the greatest promotion under the longest lighting periods. There were no differences in days to first bract color and days to anthesis when the 9-hour day was extended by 2 hours, but flowering was delayed under 4-or 6-hour EOD treatments, except for the 2-hour R+ FR + 2-hour FR and 4-hour FR treatments. Four hours of moderate-intensity EOD FR greatly promoted extension growth and delayed or prevented bract coloration in both cultivars. We conclude that EOD lighting promotes extension growth of poinsettia, and specifically, EOD FR at a low intensity (2-3 mmol.mL2.s-1) is not perceived as long-day signal, whereas a higher intensity (13 mmol.mL2.s-1) of FR delays flowering.
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