Abstract
Shorter photoperiod and lower daily light integral (DLI) limit the winter greenhouse production. Extending the photoperiod by supplemental light increases biomass production but inhibits flowering in short-day plants such as Chrysanthemum morifolium. Previously, we reported that flowering in growth-chamber grown chrysanthemum with red (R) and blue (B) LED-light could also be induced in long photoperiods by applying only blue light during the last 4h of 15h long-days. This study investigates the possibility to induce flowering by extending short-days in greenhouses with 4h of blue light. Furthermore, flower induction after 4h of red light extension was tested after short-days RB-LED light in a growth-chamber and after natural solar light in a greenhouse. Plants were grown at 11h of sole source RB light (60:40) in a growth-chamber or solar light in the greenhouse (short-days). Additionally, plants were grown under long-days, which either consisted of short-days as described above extended with 4h of B or R light to long-days or of 15h continuous RB light or natural solar light. Flower initiation and normal capitulum development occurred in the blue-extended long-days in the growth-chamber after 11h of sole source RB, similarly as in short-days. However, when the blue extension was applied after 11h of full-spectrum solar light in a greenhouse, no flower initiation occurred. With red-extended long-days after 11h RB (growth-chamber) flower initiation occurred, but capitulum development was hindered. No flower initiation occurred in red-extended long-days in the greenhouse. These results indicate that multiple components of the daylight spectrum influence different phases in photoperiodic flowering in chrysanthemum in a time-dependent manner. This research shows that smart use of LED-light can open avenues for a more efficient year-round cultivation of chrysanthemum by circumventing the short-day requirement for flowering when applied in emerging vertical farm or plant factories that operate without natural solar light. In current year-round greenhouses’ production, however, extension of the natural solar light during the first 11 h of the photoperiod with either red or blue sole LED light, did inhibit flowering.
Highlights
Flowering time is governed by various internal and external factors including developmental competence, circadian rhythms, temperature, and photoperiod (Srikanth and Schmid, 2011; Cho et al, 2017)
Extending the short-days of solar light in a greenhouse with either blue or red light to longdays did not result in flowering (Figures 4A, 5A), while the same daylight extensions after a short-day with sole source red and blue light resulted in floral initiation (Figure 4)
All plants, which were grown under red-blue short-day (RB, SD) and red-blue short days extended to long days with blue light (RB + B, LD) reached the floral initiation within 14 days from the start of the light treatment, while the plants that were grown under red-blue short-days extended with red light (RB + R, LD) reached the final floral initiation stage 5–6 days later (Figure 5B)
Summary
Flowering time is governed by various internal and external factors including developmental competence, circadian rhythms, temperature, and photoperiod (Srikanth and Schmid, 2011; Cho et al, 2017). Many plant species monitor seasonal changes in the light environment (photoperiod, light intensity, direction, and spectral composition) to optimize their growth and development (Thomas, 2006). Photoperiod influences floral induction and flowering rate in many flowering plant species. Short- and long-night plants would be more accurate as it is the length of the dark period that is decisive for flower induction (Borthwick et al, 1952). The perception of photoperiod takes place in leaves via photoreceptors that are well described in model plant species (Song et al, 2015). Photoperiodic flowering is controlled, in part, by light signals that entrain the circadian clock, which is an essential component of the mechanism for day-length sensing by plants and is involved in the regulation of flowering as explained by the “external coincidence” model for flowering (Johansson and Staiger, 2015). The control of photoperiodic flowering operates by upregulation of florigen – FLOWERING LOCUS T (FT) and downregulation of anti-florigenic FT (AFT) / TERMINAL FLOWER 1 (TFL1) under inductive photoperiod and this mechanism is conserved in both LD and SD plants (Higuchi, 2018)
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
