Increasing the Nighttime Lighting Duration Can Hasten Flowering of Long-day Plants
Date
2024-11-20
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
HortScience
Abstract
Low-intensity (≈2 μmol·m−2·s−1) photoperiodic lighting is often delivered at night to promote flowering of long-day greenhouse ornamentals when natural daylengths are short. An intermediate far-red (FR) fraction [percentage of FR light in red (R) + FR light] is necessary for the most rapid flowering in some crops, including snapdragon (Antirrhinum majus) and petunia (Petunia ×hybrida), compared with a low FR fraction. Specialty light-emitting diodes (LEDs) that include R+FR light with an intermediate FR fraction are effective at floral promotion but cost-prohibitive, whereas common warm-white (WW) LEDs with a low FR fraction can delay flowering. Because the duration to saturate flowering is longer than currently used (e.g., 4 to 8 hours) for some long-day plants, we conducted a replicated greenhouse experiment to determine how the WW or R+FR LED lighting duration influenced flowering. We grew snapdragon ‘Liberty Classic Yellow’, petunia ‘Easy Wave Burgundy Star’, and petunia ‘Wave Purple Improved’ under truncated 8-h natural short days with or without WW or R+FR (1:1) LEDs operating for 0, 4, 8, 12, or 16 hours in the middle of each night throughout the experiment. Snapdragon flowered 13 to 16 days earlier (21% to 28% earlier) under R+FR LEDs than under WW LEDs regardless of the lighting duration. Increasing the lighting duration from 0 to 16 hours decreased flowering time by up to 16 days and decreased plant height and leaf number at flowering under R+FR LEDs but not under WW LEDs. For petunia ‘Easy Wave Burgundy Star’, although WW LEDs delayed flowering by 6 to 13 days but promoted lateral branching compared with R+FR LEDs, the gap in flowering time narrowed as the lighting duration increased from 4 to 16 hours. Increasing the lighting duration improved the efficacy of WW LEDs but not R+FR LEDs. Flowering of petunia ‘Wave Purple Improved’ was unaffected as the lighting duration increased from 4 to 16 hours regardless of the lamp type and was delayed by 6 to 10 days under WW LEDs than under R+FR LEDs. For both petunia cultivars, flowering time was similar under 16-hour WW LEDs and 4-hour R+FR LEDs. In conclusion, increasing the nighttime lighting duration increased the efficacy of WW LEDs at promoting flowering of petunia and increased the efficacy of R+FR LED lamps at promoting flowering of snapdragon. Delivering WW LEDs all night long can minimize flowering delay in petunia compared with R+FR LEDs. In contrast, an intermediate FR fraction was indispensable to promote flowering of snapdragon, for which WW LEDs were ineffective.
Description
This article was originally published in HortScience. The version of record is available at: https://doi.org/10.21273/HORTSCI18175-24.
This is an open access article distributed under the CC BY-NC license (https://creativecommons.org/licenses/by-nc/4.0/).
Keywords
far-red light, floriculture, greenhouse, LED, red light, white light
Citation
Meng, Qingwu, and Thomas J. Kramer. "Increasing the Nighttime Lighting Duration Can Hasten Flowering of Long-day Plants", HortScience 59, 12 (2024): 1833-1837, accessed Dec 9, 2024, https://doi.org/10.21273/HORTSCI18175-24