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Article

The Effects of Light Treatments on Growth and Flowering Characteristics of Oncidesa Gower Ramsey ‘Honey Angel’ at Different Growth Stages

by
Chia-Man Chang
1,
Ching-Wen Wang
2,
Meng-Yuan Huang
3,
Chung-I Chen
4,
Kuan-Hung Lin
5,* and
Chih-Pei Shen
2,*
1
Tainan District Agricultural Research and Extension Station, Tainan 712, Taiwan
2
Taiwan Biodiversity Research Institute, Nantou 552, Taiwan
3
Department of Life Sciences and Innovation, Development Center of Sustainable Agriculture, National Chung Hsing University, Taichung 40227, Taiwan
4
Department of Forestry, National Pingtung University of Science and Technology, Pingtung 91201, Taiwan
5
Department of Horticulture and Biotechnology, Chinese Culture University, Taipei 11114, Taiwan
*
Authors to whom correspondence should be addressed.
Agriculture 2023, 13(10), 1937; https://doi.org/10.3390/agriculture13101937
Submission received: 6 September 2023 / Revised: 23 September 2023 / Accepted: 26 September 2023 / Published: 4 October 2023
(This article belongs to the Section Crop Production)
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Abstract

:
In our previous work, we observed that Oncidesa Gower Ramsey ‘Honey Angel’ (HA) plants became stunned on hot summer afternoons, and the seasonal trend in solar radiation affected its production schedule by limiting flower yield and quality. The objective of this work was to study the growth and flowering characteristics of HA pseudobulbs at three stages of growth (G2–G4) in response to three types of light-emitting diode (LED) lighting treatments, including full spectrum (FS), deep red/white-medium blue (DR/W-MB), and deep red/white-low blue (DR/W-LB), for two additional time intervals. The supplementary LED lighting time intervals (S) applied daily were carried out for 1 h (4:00~5:00 a.m., as S-1) or 2 h (4:00~6:00 a.m., as S-2) from March to September, 2022. Natural light without supplemental lighting was the control. The length of pseudobulb (PL), width of pseudobulb (PW), thickness of pseudobulb (PT), length of inflorescence (FL), number of branches (FB), number of florets (FN), and days to flowering (FD) per plant were recorded andcalculated when 80% of florets became mature. Light treatments significantly affected all pseudobulb growth and flower quality traits at different Gs, especially pseudobulb length (PL) and flower number (FN) under different LED types and lighting time intervals. MB-1 treatment promoted PT at both G3 and G4, whereas MB-2 treatment increased PW at both G2 and G4. Both MB-1 and LB-1 treatments had augmented effects on PL, respectively, at G2 and G3. The PW, FL, FB, and FN increased with additional light time and reached maxima under MB-2 treatment at G4 compared to other treatments and controls. Early flowering and an increased number of flowers at G4 were observed in plants grown under MB-2 treatment. Controlling light quality and supplementary light time intervals enables the production of HA plants with the desired growth and flowering quality characteristics of the pseudobulbs.

1. Introduction

The Orchidaceae family is classified into five subfamilies: Apostasioideae, Cypripedioideae, Epidendroideae, Orchidoideae, and Vanilloideae [1,2]. Oncidium, a genus encompassing approximately 330 species from the Oncidiinae subtribe within the Orchidaceae family, experiences a juvenile phase lasting 1.5–2 years, followed by blooming after each growth cycle once the current pseudobulb fully matures. The Oncidesa Gower Ramsey ‘Honey Angel (HA)’ cultivar is notably popular in Taiwan, renowned as the Golden Shower variety, extensively cultivated, and broadly utilized in the export industry [3]. Commercially employed as a cut flower, HA is a sympodial orchid featuring an enlarged internode pseudobulb developing between leaves L3 and L4 (counted from the top of each shoot). The inflorescence emerges from the pseudobulb base or leaf axil, with flower sizes ranging from 1 cm to 12.5 cm [4]. Typically, a single inflorescence arises from one location, although occasionally two inflorescences may develop. During vegetative shoot development, an inflorescence bud forms prior to the pseudobulb expansion, followed by inflorescence elongation as the pseudobulb nearly completes its expansion. HA generates inflorescences biannually. Recent studies have investigated carbohydrate fluctuations in both current and back pseudobulbs throughout vegetative and reproductive growth cycles, as well as the distinct roles of various pseudobulbs in HA development [5]. The pseudobulb starts to unsheathe from the leaf sheath when the current shoot attains a length of 30 cm. Consequently, the onset of HA pseudobulb unsheathing from its subtending leaf is a pivotal moment for reproductive growth, marked by the acceleration of inflorescence bud growth [5].
Species of Oncidium are adapted to intermediate and warmer climates and exhibit additional photoperiod responses, wherein the skotoperiod length governs flowering and development [6]. The flowering process of Oncidium can broadly be categorized into two phases: floral transition and flower development. The floral transition in orchids is influenced by key factors such as juvenility, temperature (ranging from ambient to cool), and photoperiod, all of which are instrumental in determining the timing of flowering with respect to ontogeny and season. Since most orchids originate from tropical regions where the day length experiences minimal variation throughout the year, the photoperiod exerts limited influence on orchid flowering [7]. Environmental factors or the application play significant roles in regulating and expediting plant flowering and act differently on the development of vegetative or inflorescence buds at different developmental stages [8,9]. However, they might not all necessarily be flowering signals for Oncidium. Among these factors, light intensity (LI) and quality are crucial factors influencing plant flower formation [10,11]. Orchid plants exhibit distinct morphological features under varying light conditions: they have short, plump stems and bright green leathery leaves under adequate light, scorched, yellowed, and stunted appearances under excessive light, and darker green, soft, succulent leaves with thin and spiny stems under excessive shade [12]. Oncidium plants are sensitive to abrupt and prolonged changes in light intensity (LI), which can impact their growth and flowering attributes. Although Oncidium orchids can withstand bright light, it is recommended for growers to employ a shade cloth with 30–50 percent shade in greenhouses [13]. De [12] noted that Cattleya orchids require medium to bright light irradiation of 400–600 μmol·m−2·s−1 and prosper under 40% shade cloth. Most Oncidium orchids flourish with daily exposure to one to several hours of sunlight and a LI of 500 μmol·m−2·s−1. Cymbidium plants prefer bright, dappled afternoon shade during the summer and full sunlight during the winter, but mature plants necessitate 50–55% shade during hot weather. Throughout the growing season, they demand a LI of 1000–1200 μmol·m−2·s−1, whereas, during the flowering season, they require 400–600 μmol·m−2·s−1. Oncidesa Gower Ramsey optimally grows in greenhouses under 30% shade at temperatures of 25–30 °C during the day and 20 °C at night [14]. We previously demonstrated that Oncidesa Gower Ramsey ‘Honey Angel’ (HA) exhibited a significantly higher number of branches and florets per plant under 40% LI compared to 30% LI (control) photosynthetic photon flux density (PPFD) over a period of five months [3].
Light-emitting diode (LED) lamps, which have several benefits over traditional light sources, are considered ideal for modulating plant growth and flowering characteristics [15]. These advantages include low electricity consumption, high efficiency, minimal heat emission, extended durability, compact size, and most notably, the ability to emit light at specific wavelengths and various monochromatic spectra of visible light [16]. We have previously noted that artificial supplementary lighting is necessary to complement natural daylight when solar radiation is inadequate in terms of light quantity (intensity and duration) and quality (wavelength composition) or is variable throughout the day (e.g., seasonal changes in Taiwan). This supplementary lighting was primarily utilized to enhance the photosynthetic performance of Oncidesa Gower Ramsey ‘Honey Angel’ (HA), thereby increasing its annual productivity and ensuring consistency in flower product yield and quality (unpublished data). Conversely, HA entered a dormant state under the intense lighting conditions of hot summer afternoons (e.g., 1300 to 1500 μmol·m−2·s−1), during which lighting conditions remained largely unregulated. This seasonal variation in solar radiation influenced the production schedule by constraining plant yield and quality. In addition, high summer temperatures cause the photosynthesis of HA plants to become dormant during the afternoon, leading to an insufficient accumulation of photosynthetic products and a decrease in the length of cut flowers and the number of branches and florets. Therefore, the double-layer shade net was used to reduce high temperatures, but decreases in the stemming rate and poor quality of cut flowers were subsequently observed. Moreover, we tried other lighting strategies to provide cyclic or intermittent lighting. During cyclic lighting, LEDs were turned on and off at specific intervals for particular durations.
To date, no study has investigated the effects of supplementary lighting periods using various LED wavelengths on HA growth and flowering characteristics during different growth stages. In fact, it poses a challenge to select the most effective light spectrum for each species [17,18]. For example, red light impacts the development of the photosynthetic apparatus, and both red and blue lights are most efficiently utilized for photosynthesis [19]. Blue light affects stomatal opening, plant height, and chlorophyll biosynthesis, whereas far-red light promotes flowering in long-day plants, and the red/far-red ratio regulates stem elongation, branching, leaf expansion, and reproduction [10]. Lastly, green light facilitates long-term development and short-term acclimation to light conditions, thereby enhancing crop productivity and yield [20]. HA’s unusual dormant afternoon behavior indicates that supplementary lighting during the early morning hours before sunrise could improve flower quality. Supplementary lighting might control the flowering ability of HA because it flowers at the end of each growth cycle, regardless of the season. Since no research has been conducted on the relationship between flowering and supplementary light treatment in Oncidium, the present study aims to use supplementary light emitted by white and red LEDs supplemented with additional wavelength ranges of blue LEDs to increase HA pseudobulb growth and flowering quality under optimal temperature and light intensity. This study hypothesizes that plants may alter their periodic and oscillator systems during growth under artificial supplementary lighting conditions, develop adaptive mechanisms for the tropical environment, and survive during minimal fluctuations. The findings of this study hold significant implications for the marketing of Oncidium cut flowers, and through the implementation of lighting control technologies, commercial production can be optimized. Furthermore, comprehending the adaptive mechanisms of Oncidium to supplemental LED treatments at different growth stages can facilitate the maximization of its growth, development, and flowering characteristics.

2. Materials and Methods

2.1. Plant Materials and Cultural Practices

The Oncidesa Gower Ramsey ‘Honey Angel’ cultivar (HA) plants in this study were cultivated over an extended period at the Tainan District Agricultural Research and Extension Station (TDARES) in Tainan City, Taiwan, and maintained in a greenhouse from March to September 2022. The selected plants were two years old, measuring 10–20 cm in height with 4–5 leaves, and possessed at least two pseudobulbs and well-branched inflorescences with unopened flower buds and 50% open florets (inflorescence stage; Figure 1). Subsequently, the inflorescences were removed, and the plants were transplanted into plastic pots (1.6 L, one plant per pot) containing commercial potting soil mixed with crushed stone and charcoal in a 3:1 ratio. These pots were then placed in a TDARES greenhouse under specific conditions: an 8-h photoperiod, day/night temperatures of 30/25 °C, an average relative humidity of 80%, and a photosynthetic photon flux density (PPFD) of 300 μmol s−1. A rigid frame covered with 60% shading nets was used to reduce light penetration. The cultural practices followed were consistent with those detailed in our previous paper [3]. In summary, the plants were watered daily and received a weekly application of an optimal amount of compound water-soluble fertilizer solution (N: P2O5: K2O, 20:20:20; Scott, Marysville, OH, USA) at a concentration of 1 g L−1 until the experiment concluded. A microclimate station (Watch Dog 2475 Weather Station, Spectrum Technologies, Aurora, IL, USA) was strategically positioned in the center of each study plot to record the temperature, PPFD, and relative humidity.
For this study, plants having different lengths of the flower stalk during three growing stages are defined as follows:
(1). Growing stage 2: plants in the plantlet stage prior to unsheathing with vegetative shoots 10~20 cm in height, (2). Growing stage 3: plants ina pseudobulb-mature stage have flower stalks 3–6 cm in length, and (3). Growing stage 4: plants ina pseudobulb-mature stage with flower stalks 20–35 cm in length and shorter than plant height.
Each stage had 10 single plant replications, and uniformly sized plants were selected and separated randomly into six groups for the light treatments in Section 2.2. Each group was treatedthe same as the environmentally controlled greenhouse mentioned aboveduring the 7-month experiment period of culture conditions.

2.2. Supplemental Light Treatment (SL)

Daily supplemental LED lighting was applied to plants for 1 h from 4:00 a.m. to 5:00 a.m. or 2 h from 4:00 a.m. to 6:00 a.m., from 1 March 2022, until cut flowers were harvested. Three different types of LEDs with two supplementary time intervals were applied as follows (Figure 2):
  • Control treatment was natural light in the greenhouse, with no artificial light source added;
  • Full spectrum (FS) LED (EL-B05L1200-DSM-D4890W, >350 μmol·m−2·s−1at 30 cm, 400–700nm, SOLIDLITE, Taipei, Taiwan) for 1 h (subsequently referred to as FS-1) and 2 h (subsequently referred to as FS-2);
  • Deep red/white (DR/W)—medium blue (MB) (Philips Green Power LED, Philips, The Netherlands), primary light colors being DR/W with typical PPFD 800 m−2 s−1, power consumption 285W, 400–750nm, and efficacy 2.8 μmol J−1, for 1 h (subsequently referred to as MB-1) and 2 h (subsequently referred to as MB-2) period;
  • Deep red/white (DR/W)—low blue (LB) (Philips Green Power LED, Philips, The Netherlands), primary light colors being DR/W with typical PPFD 800 m−2 s−1, power consumption 275W, 350–750nm, and efficacy 2.9 μmol J−1, for 1 h (subsequently referred to as LB-1) and 2 h (subsequently referred to as LB-2).
All light sources were installed on the plant culture rack and controlled separately by a central processor (layer number/layer height/layer length/layer width: 6/40 cm/1200 cm/600 cm tailor-made). The mean photosynthetic daily light integral measured at each location ranged from 300 to 400 μmol s−1. Natural light without supplementary lighting was used as the control.
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Figure 2. (A) Schematic illustration of the application of LEDs in different plant growing stages (G2, G3, and G4) in HA greenhouse culture. Daily supplemental LED lighting applied to plants was carried out for 1 h from 4:00 a.m. to 5:00 a.m. or 2 h from 4:00 a.m. to 6:00 a.m. from 1 March 2022, until cut flowers were harvested. When plants were 2yearsold and 10~20 cm in height with 4–5 leaves, they had at least 2 pseudobulbs. Plants were divided into 3 groups (G2, G3, and G4) for each of six supplemental lighting treatments. A total of 105 pots with 5 replicates of each treatment were arranged in a completely randomized design. (B–D) Three different types of LEDs were used: full spectrum (B), deep red/white type—medium blue (C), and deep red/white type—low blue (D).
Figure 2. (A) Schematic illustration of the application of LEDs in different plant growing stages (G2, G3, and G4) in HA greenhouse culture. Daily supplemental LED lighting applied to plants was carried out for 1 h from 4:00 a.m. to 5:00 a.m. or 2 h from 4:00 a.m. to 6:00 a.m. from 1 March 2022, until cut flowers were harvested. When plants were 2yearsold and 10~20 cm in height with 4–5 leaves, they had at least 2 pseudobulbs. Plants were divided into 3 groups (G2, G3, and G4) for each of six supplemental lighting treatments. A total of 105 pots with 5 replicates of each treatment were arranged in a completely randomized design. (B–D) Three different types of LEDs were used: full spectrum (B), deep red/white type—medium blue (C), and deep red/white type—low blue (D).
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2.3. The Assessments of Plant Growth and Flowering Quality

The vegetative stages of the bud stage and plantlet lasted for 3~4 months, followed by the unsheathing phase for one more month, and the last stage exhibiting florescence for 1.5~2 months. The measurements of plant growth and flowering quality were carried out on harvested flowers based on our previous paper [3], as listed below. The flowering date was recorded for each plant as being when the first floret opened. After the seven-month testing period, every analysis was carried out when more than 80 percent of the florets on the spikes were fully open (Figure 3). Ten plants were randomly assigned to each individual lighting treatment.
  • Pseudobulb length (PL) was measured with a Vernier caliper as the long axis (mm) between the base and top of a pseudobulb.
  • Pseudobulb width (PW) was measured with a Vernier caliper as the short axis (girth, mm) of a pseudobulb.
  • Pseudobulb thickness (PT) was measured as the maximum thickness (mm) of a pseudobulb.
  • Inflorescence length (FL) was measured with a Vernier caliper as the length (mm) between the base and top of a flower stalk.
  • Number of branches (FB) was recorded as all the branches of a flower stalk.
  • Number of florets (FN) was recorded as all the florets (unopened buds and opened florets) of a flower stalk.
  • Days to flowering (FD) was recorded as the number of days from the start of light treatment until flower harvest.
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Figure 3. The methodology and experimental design used in this study. The length of pseudobulb (PL), width of pseudobulb (PW), thickness of pseudobulb (PT), length of inflorescence (FL), number of pedicels (FB), number of florets (FN), and days to flowering (FD) in ‘Honey Angel’ (HA) cultivated under LED light treatments at three growing stages (G2, G3, and G4). Supplemental lighting was provided to all treatments for 1–2 h, from 4:00 a.m. to 5:00 a.m. or from 4:00 a.m. to 6:00 a.m., respectively, by LEDs that delivered a full spectrum (FS) LED for 1 h and 2 h, deep red/white type (DR/W)—medium blue (MB) LED for 1 h and 2 h period, and deep red/white type (DR/W)—low blue (LB) LED for 1 h and 2 h. Natural light without supplementary lighting was used as the control.
Figure 3. The methodology and experimental design used in this study. The length of pseudobulb (PL), width of pseudobulb (PW), thickness of pseudobulb (PT), length of inflorescence (FL), number of pedicels (FB), number of florets (FN), and days to flowering (FD) in ‘Honey Angel’ (HA) cultivated under LED light treatments at three growing stages (G2, G3, and G4). Supplemental lighting was provided to all treatments for 1–2 h, from 4:00 a.m. to 5:00 a.m. or from 4:00 a.m. to 6:00 a.m., respectively, by LEDs that delivered a full spectrum (FS) LED for 1 h and 2 h, deep red/white type (DR/W)—medium blue (MB) LED for 1 h and 2 h period, and deep red/white type (DR/W)—low blue (LB) LED for 1 h and 2 h. Natural light without supplementary lighting was used as the control.
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2.4. Statistical Analysis

A total of seven light treatments (control, FS-1, FS-2, MB-1, MB-2, LB-1, and LB-2) and three growing stages (G2, G3, and G4) were selected as the experimental variables. A completely random design was used to conduct the analysis with 35 plants (replicates) for each type of LED (control, FS, MB, and LB), each growing stage (G2, G3, and G4),and each supplementary LED time (code-named S for 1 h and 2 h, and control for 2 h). The experimental design consisted of 4 treatments, 3 growth stages, and 2 supplemental light intervals with 5 replications, resulting in a total of 105 pots. Using CoSt at 6.4 (Co Hort Software, Monterey, CA, USA), the analysis of variance (ANOVA) was used to determine the significance of the measurements of the seven horticultural traits, and the treatment means were separated by the Tukey’s HSD test at p ≤ 0.05.

3. Results

This study evaluated the impacts of seven light treatments (L, including control, FS-1, FS-2, MB-1, MB-2, LB-1, and LB-2) on ‘Honey Angel’ (HA) plants across three growing stages (G, including G1, G2, and G3) by measuring changes in length of pseudobulb (PL), width of pseudobulb (PW), thickness of pseudobulb (PT), flower length (FL), flower breadth (FB), flower number (FN), and flower diameter (FD). The experiment assumed interdependence between each light treatment and the growing stage. Table 1 demonstrates that all measured traits exhibited significant differences at the 1%, 5%, 0.1%, or 0.01% levels for all main effects and at the 1% or 0.01% levels for all interaction effects. This implies that light treatments considerably influenced all pseudobulb growth and flower quality traits at different growing stages. Furthermore, after applying four types of lights (T, including control, FS, MB, and LB) under two supplementary time intervals (S, 1 h and 2 h) to HA plants, the pseudobulb growth and flower quality traits, as documented in Table 2, showed significant differences at the 5% or 0.1% levels under the four types of lights, except for PL and FN, which exhibited nonsignificant differences among T. Additionally, all traits exhibited nonsignificant differences in the S effect and the T × S interaction, except for PL, which differed significantly at the 1% level. This suggests that the effects of different LEDs on PL and FN under varying supplementary time intervals might differ across plant growth stages.
When growing stages (G) are compared across types of light (T) and supplementary time interval (S) treatments, Table 3, Table 4 and Table 5 demonstrate the influences of T and S on pseudobulb growth and flower quality of HA cultivated in G2~4. All traits under the T effect significantly differed in growing stage 2 (G2), except for PL and FB. In contrast, all traits under the S effect did not show significant differences, except for PW, PT, and FD, with p ≤ 0.05, p ≤ 0.01, and p ≤ 0.05, respectively (Table 3). Only PL in G2 appeared to significantly differ (p ≤ 0.0001) in the interactive effect T × S. The effects of T and S on pseudobulb growth and flower quality cultivated in G3 showed that all measurements were significant at the levels of 1% or 5% for T × S interaction effects, except for PL and FN showing non-significance (Table 4). PT, FB, FN, and FD traits showed significant differences in the T effect at the 5%, 0.1%, or 0.01% levels, whereas PW, PT, and FL traits significantly differed in the S effect at the 0.1% or 0.01% level. The effects of S on G4 of HA during T treatments were monitored by measuring changes in pseudobulb growth and flower quality (Table 5). All traits displayed nonsignificant differences in the main effects, except for PW, FB, FN, and FD in the T effect at the 0.01% or 0.0001% level and FD in the S effect at the 0.01% level. Moreover, flower quality indices FB, FN, and FD were significantly different (p < 0.01 or 0.0001) in the interaction effect (T × S).
Results of seven light treatments’ horticultural evaluation generated from three types of LEDs and two supplementary light durations (S) of HA cultivated at three different growing stages are presented in Figure 4 and Figure 5, and phenotypic variations among treatments are apparent. Figure 4 illustrates that the mean values of PL, PW, and PT in FS-2, MB-2, and LB-2treatments are significantly higher than in FS-1, MB-1, and LB-1 treatments during the G2 stage (Figure 4A,D,G). However, significantly lower PL (68.26 mm) occurred in MB-2 compared to MB-1 (81.26 mm, Figure 4A), and nonsignificant differences in PW were exhibited between LB-1 (32.53 mm) and LB-2 treatments (33.70 mm, Figure 4D). Different light treatments significantly influenced PL in G2 compared to controls, except that PL under FS-1 and MB-2 treatments showed non-significances. Significantly lower compared tothe control (Figure 4A). However, light treatments significantly reduced PW and PT in G2 compared to controls, except that significantly higher PW under MB-2 treatment (Figure 4D) and significantly higher PT under MB-2 and LB-2 treatments (Figure 4G) were observed compared to controls. A significantly longer PL of G3 was detected in MB-1 and LB-1 treatments (respectively 76.19 mm and 83.81 mm) than in MB-2 and LB-2 treatments (respectively 70.84 mm and 75.4 mm) (Figure 4B). A similar trend was found in PW and PT values at G3, and FS-1 and MB-1-treated plants had significantly higher PW and PT values compared to FS-2 and MB-1 treatments (Figure 4E,H), indicating that different light treatments affected pseudobulb traits differently. Different light treatments significantly influenced all pseudobulb growth traits in G4 compared to controls (Figure 4C,I), except that PW under FS treatments did not show significance against controls (Figure 4F). In G4, all six light treatments significantly increased PL values (78.62~84.02 mm) compared to controls (70.66 mm) (Figure 4C). HA plants treated with MB-2 and LB-2 at G4 exhibited significantly higher PW at 39.23 mm and 36 mm, respectively, than with MB-1 and LB-1 at 36.84 mm and 33.77 mm, respectively (Figure 4F). Similarly, the PT value at G4 of LB-2-treated plants was significantly higher (24.93 mm) compared to LB-1 treatments (22.64 mm) (Figure 4I).
Flower quality traits were measured to analyze the effects of different light treatments on flower characteristics under different growing stages (Figure 5). The FL and FN values from MB-2 (107 cm and 86.6, respectively) and LB-2 (96 cm and 57.33, respectively) treatments during G2 were significantly higher than MB-1 (99.5 cm and 71, respectively) and LB-1 (91 cm and 51.67, respectively) treatments (Figure 5A,G). The longest FL and highest FN of G2 were detected in the MB-2 treatment compared to other treatments and controls. Nevertheless, no light treatment affected the FB in G2 (Figure 5D). A significantly higher FDwas treated with FS-1 and LB-1 lights compared to FS-2 and LB-2 treatments, and the longest FD was 146.33days (d) under LB-2 treatment (Figure 5J). However, Figure 5B shows that HA plants treated with FS-2, MB-2, and LB-2 at G3 had significantly shorter FL (108, 104, and 102cm, respectively) than with FS-1, MB-1, and LB-1 treatments (111.5, 122.83, and 111.6 cm, respectively). Notably, the FL, FB, and FN values of G3 significantly increased under MB-1 treatment compared to the other treatments and controls, and the highest FB and FN under MB-1 treatment were recorded as 11 and 123.67, respectively (Figure 5E,H). Figure 2K shows a significant increase in FD occurred in LB-2 treatment at 100.2 d compared to controls andLB-1 treatment at 94.75 and 89.2 d, respectively. Interestingly, HA plants subjected to MB-2 treatment at G4 significantly increased their FL (106.67 cm), FB (9.67), and FN (100 d) compared to the other treatments and controls (Figure 5C,F,I). However, all light treatments seemed to strongly affect FD at G4 compared to controls, and MB-treated plants displayed the shortest number of days (60 d) to flowering (Figure 5L).

4. Discussion

4.1. Effects of Different LEDs on HA Pseudobulb Growth at Different Growing Stages

Plants have a circadian clock that regulates physiological events by anticipating daily environmental changes, and photosynthesis is governed by this clock, an endogenous oscillator influenced by external factors such as light [22]. Our supplementary lighting system, which uses stationary LEDs, successfully prevented afternoon stunning in ‘Honey Angel’ (HA). It is hypothesized that the enhancement of pseudobulb growth by 1 or 2 h of daily supplementary LED lighting is associated with the varied photo-equilibrium of photoreceptors, which encourages a decrease in apical dominance and the growth of the pseudobulb base, leaf axils, and axillary buds. Pseudobulbs are crowned with one or more small leaves that are soft, pencil-like, leathery, and thick. Figure 4 shows that the supplementary LED lighting was evaluated for pseudobulb growth under various growing stages.MB-1 treatment operated continuously throughout the early morning from 4:00~5:00 a.m. and promoted PT at both G3 and G4 but prevented PT development at G2 compared to controls, whereas MB-2 treatment ameliorated PW at both G2 and G4 but precluded PW development at G3 compared to controls. In addition, MB-1 and LB-1 treatments had augmented effects on PL at G2 and G3, respectively, compared to controls. Applying LED light enhanced the pseudobulb length (PL), pseudobulb width (PW), and pseudobulb thickness (PT), thereby facilitating acclimatization to the natural environment. Comprehending these morphological alterations allows the creation of models for optimal ‘Honey Angel’ (HA) processing times at various growth stages, tailored to meet distinct industry requirements.
Recent literature has extensively examined the impacts of LEDs on plant morphogenesis, indicating that blue light augments the count of axillary buds [18,23,24]. Conversely, it impedes bud sprouting and intensifies apical dominance. Furthermore, the diminished bud outgrowth under blue light exposure underscores its role in particular photoreceptors and its function as a phytochrome antagonist. Sakurako et al. [25] elucidate that blue LEDs augment chlorophyll biosynthesis and stomatal opening, while Song et al. [26] indicate that they are favorable for Anthurium andreanum’s shoot growth, dry matter accumulation, photosynthetic rate, soluble sugar, and antioxidant activity. Concurrently, studies by Izzo et al. [27] and Yousef et al. [28] demonstrate that a red and blue LED combination promotes tomato plant growth. Shin et al. [29] also observe that quality Orchidaceae Doritaenopsis plants result from in vitro culturing under a mix of blue and red LEDs. Additionally, Liu et al. [30] disclose that, compared to red LED, blue LED hinders Oncidium stem growth but enhances soluble protein levels in protocorm-like bodies (PLB) and leaves, implying blue light’s benefits for protein synthesis. Additionally, blue LED treatment leads to a higher PLB percentage and a 1.5-fold increase in Dendrobium officinale shoots [31]. It also amplifies the regenerated shoot count from PLB in Cattleya intermedia × C. aurantiaca [32]. In this study, the MB-1, MB-2, and LB-2 treatments triggered specific responses to PL, PW, and PT at G2, respectively. This underlines the necessity to account for light duration and spectrum sensitivity when tailoring lighting protocols for commercial farms. Furthermore, if the growing stages’ coverage is insufficient, additional supplemental light treatments would be necessary.

4.2. Influences of Different LEDs on Flower Quality in HA at Different Growing Stages

Oncidium species are considered to have high economic value for cut flowers and as potted plants due to their varied and attractive colors and branches, long shelf life, high productivity, and year-round blooming. HA has excellent potential in the tropical and subtropical regions in Taiwan for the production of cut flowers and potted plants. The production of Oncidium species requires delivery to markets in full bloom on specific dates, as consumers generally prefer to purchase flowering plants over vegetative plants. Supplementary lighting duration can be manipulated to induce Oncidium pseudobulb growth and quality flowering by adopting a suitable package of practices and intensive management, which indicates the commercial viability of their cut flowers. Figure 4 and Figure 5 show the supplementary LED lighting durations evaluated for HA commercial production at different growth stages, and results showing differences between pseudobulb growth and flower quality traits and sensitivity to supplementary lighting. MB-1 improved PL but reduced FL, FN, and FD at G2, whereas MB-2 improved PW, PT, FL, and FN at G2, indicating that increased supplementary time augmented pseudobulb growth, elongated flower stems, and increased flower numbers. MB-1 treatment prolonged PT and FL with expanded FB and FN at G3 compared to other treatments and controls, indicating that MB light induced shorter apical buds and increased leaf exposure. PW, FL, FB, and FN increased with treatment duration and red-light proportion and reached their maximum values under MB-2 treatment at G4 compared to other treatments and controls. Meanwhile, early flowering and an increased number of flowers at G4 were observed in plants grown under MB-2 treatment. The number of flowers on 30 September in controls, TS-1, TS-2, MB-1, MB-2, LB-1, and LB-2 treatments at G4 were 96.6, 132.33, 80, 127, 154, 91.67, and 100 flowers, respectively, indicating that MB spectral quality had a significantly favorable influence on the rate of HA flower bud production. The two different blue LEDs, MB and LB, have complex regulation effects on pseudobulb growth and flower quality; the specific mechanism is still unclear and needs further study.
Flowering timing is a vital horticultural characteristic for floriculture crops, and achieving a consistent flowering time remains a key objective in breeding programs to introduce new horticultural innovations in commercial crops. Various light treatments demonstrated varying effects on the number of days to HA flowering at different growth stages. Notably, supplementary lighting with MB introduced at G4 resulted in a remarkable reduction to 60 d for flowering, proving to be more effective in promoting flowering compared to the control group, which required 80 days to flower. The first flowering was observed on 2 May and 3 May in MB-1 and MB-2 treatments at G4, respectively, while it was on 1 August in controls. Similarly, the time to visible HA flowering in the longest days at G2 increased from 130 days for controls to 148 d under LB-2 treatment. The initiation of flowering in the LB-2 treatment and controls occurred on 19 June and 21 July, respectively. Light, functioning as an environmental signal, is perceived by a companion detection system that orchestrates plant photomorphogenetic responses, including transitions between developmental stages. Photoreceptors receive light signals and modulate growth, differentiation, and metabolism. Flowering under MB light is intricate, involving interactions among photoreceptors, an endogenous circadian clock, and flowering genes [33]. During HA plant development, light influences pseudobulb elongation, leaf expansion, plant architecture, and ultimately, the transition to flowering. The interplay among these components remains ambiguous and warrants further investigation. Evaluating HA flower production and quality is crucial for assessing the economic viability of cultivation. Enhancing production and quality entails increasing the number of flowers per plant, pedicels (branches) per flower, and flower size or length. Spectral quality markedly impacts the plant growth period, pseudobulb leafing, flowering time, and flower characteristics. Hence, understanding these effects is pivotal for selecting light sources that promote prolonged flowering periods and high flower and pedicel production in HA. This enables commercial ornamental growers to establish artificial supplementary lighting intervals, ensuring year-round flowering and marketing of Oncidium species.

5. Conclusions

Oncidium plants, grown globally, hold significant economic value. This study investigates the impact of supplementary LED treatments on the pseudobulb growth and floral traits of HA Oncidium. A factorial experiment, encompassing T and S treatments at each G, was executed in a completely randomized design with ten replications (plants), revealing variations in pseudobulb and flower quality traits across T, S, and G. Specifically, MB light treatments notably influenced HA plant growth and development, with MB-1 and MB-2 at G2 being particularly effective, demonstrating their potential as suitable indoor lighting environments to enhance PL, PW, and PT. Moreover, the beneficial effects of MB-1 at G3 and MB-2 at G4 on HA were more pronounced, resulting in increased FL, FB, and FN, particularly accelerating flowering. Careful management of supplemental LED treatments across different growth stages enables the optimization of HA growth, development, and flowering traits. Additionally, this strategy can successfully adjust the seasonal flowering patterns of Oncidium species, encouraging shorter vegetative periods and more frequent flowering. Investigating the continuous flowering mechanism further could facilitate the design of functional studies aiming to trigger a flowering revolution in valuable Oncidium species.

Author Contributions

Conceptualization, C.-M.C.; methodology, K.-H.L., M.-Y.H. and C.-I.C.; investigation, C.-P.S. and C.-W.W.; resources, C.-M.C. and C.-P.S.; data curation, M.-Y.H. and C.-I.C.; writing—original draft preparation, K.-H.L. and C.-W.W.; writing—review and editing, K.-H.L. and C.-W.W.; supervision, C.-P.S. and C.-M.C. All authors have read and agreed to the published version of the manuscript.

Funding

This work was partially supported by the Taiwan Government Department for the Taiwan Biodiversity Research Institute.

Institutional Review Board Statement

Not applicable.

Data Availability Statement

The data and materials are available upon reasonable request from the corresponding author.

Acknowledgments

The authors thank Tainan District Agricultural Research and Extension Station for the financial support.

Conflicts of Interest

The authors declare no conflict of interest.

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Figure 1. Schematic illustration of Oncidesa Gower Ramsey’s ‘Honey Angel (HA)’ vegetative and reproductive cycles. Oncidesahas a juvenile stage of 1.5–2 years and then flowers at the end of each growth cycle after the current pseudobulb expands entirely. It is commercially used as cut flowers and is a sympodial orchid with an enlarged internode pseudobulb developed between the third and fourth leaves counted from the top of each shoot. Usually, a single inflorescence is produced from a single growth, or, in some cases, two inflorescences may be produced. Inflorescences develop from the base of the pseudobulb or the axils of leaves. In the developing vegetative shoot, an inflorescence bud forms before the pseudobulb expands, and then the inflorescence elongates when the pseudobulb is nearly fully expanded. HA produces inflorescences twice every year. (A) plantlet stage. (B) unsheathing stage (C) pseudobulb maturing stage. (D) pseudobulb with early inflorescence stage. (E) blooming stage (F) pseudobulb with early axillary bud. (G) pseudobulb with newly plantlet. (C) to (F) vegetative cycle. (D) to (E) reproductive cycle. Leaf is indicated from the top of the pseudobulb noted as L1, L2, L3, L4. (Replotted from Chin et al. [21]).
Figure 1. Schematic illustration of Oncidesa Gower Ramsey’s ‘Honey Angel (HA)’ vegetative and reproductive cycles. Oncidesahas a juvenile stage of 1.5–2 years and then flowers at the end of each growth cycle after the current pseudobulb expands entirely. It is commercially used as cut flowers and is a sympodial orchid with an enlarged internode pseudobulb developed between the third and fourth leaves counted from the top of each shoot. Usually, a single inflorescence is produced from a single growth, or, in some cases, two inflorescences may be produced. Inflorescences develop from the base of the pseudobulb or the axils of leaves. In the developing vegetative shoot, an inflorescence bud forms before the pseudobulb expands, and then the inflorescence elongates when the pseudobulb is nearly fully expanded. HA produces inflorescences twice every year. (A) plantlet stage. (B) unsheathing stage (C) pseudobulb maturing stage. (D) pseudobulb with early inflorescence stage. (E) blooming stage (F) pseudobulb with early axillary bud. (G) pseudobulb with newly plantlet. (C) to (F) vegetative cycle. (D) to (E) reproductive cycle. Leaf is indicated from the top of the pseudobulb noted as L1, L2, L3, L4. (Replotted from Chin et al. [21]).
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Figure 4. Supplemental lighting was provided to all treatments for 1 or 2 h, from 4:00 a.m. to 5:00 a.m. or 4:00 a.m. to 6:00 a.m., respectively, by LEDs that delivered full spectrum (FS), medium blue (MB), and low blue (LB) LEDs to the plants at three stages of growth (G2~G4). HA values for pseudobulb length (PL, A–C), pseudobulb width (PW, D–F), and pseudobulb thickness (PT, G–I) are in response to seven lighting treatments (control, FS-1, FS-2, MB-1, MB-2, LB-1, and LB-2) cultivated at growing stages G2 (A,D,G), G3 (B,E,H), and G4 (C,F,I). Control plants were grown under natural light without supplementary light treatment. At the end of the experimental period, data were collected and calculated after two months of pseudobulb maturity culture. According to Tukey’s HSD test, the means within the same growing stage of all light treatments that are followed by various lowercase letters differ at p ≤ 0.05. The mean and standard errors are shown by vertical bars (n = 5).
Figure 4. Supplemental lighting was provided to all treatments for 1 or 2 h, from 4:00 a.m. to 5:00 a.m. or 4:00 a.m. to 6:00 a.m., respectively, by LEDs that delivered full spectrum (FS), medium blue (MB), and low blue (LB) LEDs to the plants at three stages of growth (G2~G4). HA values for pseudobulb length (PL, A–C), pseudobulb width (PW, D–F), and pseudobulb thickness (PT, G–I) are in response to seven lighting treatments (control, FS-1, FS-2, MB-1, MB-2, LB-1, and LB-2) cultivated at growing stages G2 (A,D,G), G3 (B,E,H), and G4 (C,F,I). Control plants were grown under natural light without supplementary light treatment. At the end of the experimental period, data were collected and calculated after two months of pseudobulb maturity culture. According to Tukey’s HSD test, the means within the same growing stage of all light treatments that are followed by various lowercase letters differ at p ≤ 0.05. The mean and standard errors are shown by vertical bars (n = 5).
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Figure 5. Supplemental lighting was provided to all treatments for 1 or 2 h, from 4:00 a.m. to 5:00 a.m. or 4:00 a.m. to 6:00 a.m., respectively, by LEDs that delivered full spectrum (FS), medium blue (MB), and low blue (LB) lighting to plants at three stages of plant growth (G2~G4). HA inflorescence length (FL, A–C), number of pedicels (FB, D–F), floret numbers (FN, G–I), and days to flowering (FD, J–L) respond to seven light treatments (control, FS-1, FS-2, MB-1, MB-2, LB-1, and LB-2) under cultivation at growth stages G2 (A,D,G,J), G3 (B,E,H,K), and G4 (C,F,I,L). Control plants were grown under natural light without supplementary light treatment. At the end of the experimental period, data were collected and calculated after two months of pseudobulb cultivation. According to the Tukey’s HSD test, the means of all light treatments that are followed by various lowercase letters substantially differ at the same growth stage at p ≤ 0.05. Each treatment was dependent on the others. The mean and standard error are shown by vertical bars (n = 5).
Figure 5. Supplemental lighting was provided to all treatments for 1 or 2 h, from 4:00 a.m. to 5:00 a.m. or 4:00 a.m. to 6:00 a.m., respectively, by LEDs that delivered full spectrum (FS), medium blue (MB), and low blue (LB) lighting to plants at three stages of plant growth (G2~G4). HA inflorescence length (FL, A–C), number of pedicels (FB, D–F), floret numbers (FN, G–I), and days to flowering (FD, J–L) respond to seven light treatments (control, FS-1, FS-2, MB-1, MB-2, LB-1, and LB-2) under cultivation at growth stages G2 (A,D,G,J), G3 (B,E,H,K), and G4 (C,F,I,L). Control plants were grown under natural light without supplementary light treatment. At the end of the experimental period, data were collected and calculated after two months of pseudobulb cultivation. According to the Tukey’s HSD test, the means of all light treatments that are followed by various lowercase letters substantially differ at the same growth stage at p ≤ 0.05. Each treatment was dependent on the others. The mean and standard error are shown by vertical bars (n = 5).
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Table 1. The pseudobulb length (PL), pseudobulb short axis (PW), pseudobulb thickness (PT), inflorescence length (FL), number of pedicels (FB), floret numbers (FN), and days to flowering (FD) per plant were examined by analysis of variance for the effects of light treatment (L), growth stage (G), and their interaction (L × G).
Table 1. The pseudobulb length (PL), pseudobulb short axis (PW), pseudobulb thickness (PT), inflorescence length (FL), number of pedicels (FB), floret numbers (FN), and days to flowering (FD) per plant were examined by analysis of variance for the effects of light treatment (L), growth stage (G), and their interaction (L × G).
TraitMain and Interaction Effects
LGL × G
F and p Values with Significance
FpFpFp
PL (mm)5.810.00001 ****7.210.001 **2.680.005 **
PW (mm)4.630.0005 ***15.690.00001 ****6.440.00001 ****
PT (mm)4.330.0009 ***3.180.05 *5.870.00001 ****
FL(cm)7.020.00001 ****24.100.00001 ****4.430.00001 ****
FB3.950.001 **76.440.00001 ****4.800.00001 ****
FN19.380.00001 ****83.210.00001 ****6.820.00001 ****
FD (day)9.490.00001 ****836.20.00001 ****4.950.00001 ****
* p ≤ 0.05, ** p ≤ 0.01, *** p ≤ 0.001, **** p ≤ 0.0001. n = 35, 15, and 105 plants (replicates) for L, G, and L × G, respectively.
Table 2. The pseudobulb length (PL), pseudobulb short axis (PW), pseudobulb thickness (PT), inflorescence length (FL), number of pedicels (FB), floret numbers (FN), and days to flowering (FD) per plant were examined by analysis of variance for the effects of type of light source (T), supplemental light duration (S), and their interaction (T × S).
Table 2. The pseudobulb length (PL), pseudobulb short axis (PW), pseudobulb thickness (PT), inflorescence length (FL), number of pedicels (FB), floret numbers (FN), and days to flowering (FD) per plant were examined by analysis of variance for the effects of type of light source (T), supplemental light duration (S), and their interaction (T × S).
TraitMain and Interaction Effects
TST × S
F and p Values with Significance
FpFpFp
PL (mm)0.860.43 NS2.570.11 NS5.550.005 **
PW (mm)4.240.02 *0.100.75 NS0.850.43 NS
PT (mm)4.660.01 *0.010.91 NS0.920.40 NS
FL(cm)3.350.04 *0.710.40 NS0.040.96 NS
FB3.350.04 *0.380.53 NS0.100.91 NS
FN9.010.0003 ***0.020.89 NS1.030.36 NS
FD (day)0.290.75 NS0.040.85 NS0.290.75 NS
* p ≤ 0.05, ** p ≤ 0.01, *** p ≤ 0.001, NS nonsignificant difference. n = 35, 15, and 105 plants (replicates) for T, S, and T × S, respectively.
Table 3. The pseudobulb length (PL), pseudobulb short axis (PW), pseudobulb thickness (PT), inflorescence length (FL), number of pedicels (FB), floret numbers (FN), and days to flowering (FD) per plant at growth stage2 (G2), (FN), and days to flowering (FD) of per plant were examined by analysis of variance for the effects of type of light source (T), supplemental light duration (S), and their interaction (T × S).
Table 3. The pseudobulb length (PL), pseudobulb short axis (PW), pseudobulb thickness (PT), inflorescence length (FL), number of pedicels (FB), floret numbers (FN), and days to flowering (FD) per plant at growth stage2 (G2), (FN), and days to flowering (FD) of per plant were examined by analysis of variance for the effects of type of light source (T), supplemental light duration (S), and their interaction (T × S).
TraitMain and Interaction Effect
TST × S
F and p Values with Significance
FpFpFp
PL (mm)0.690.51 NS0.440.51 NS33.520.00001 ****
PW (mm)5.680.009 **6.240.02 *0.610.55 NS
PT (mm)9.580.0008 ***10.870.003 **0.0750.93 NS
FL(cm)5.880.008 **4.620.042 NS0.290.75 NS
FB2.180.13 NS0.0010.97 NS0.0010.99 NS
FN10.190.0005 ***2.030.17 NS1.080.35 NS
FD (day)12.130.0002 ***7.250.01 *2.130.14 NS
* p ≤ 0.05, ** p ≤ 0.01, *** p ≤ 0.001, **** p ≤ 0.0001, NS nonsignificant difference. n = 35, 15, and 105 plants (replicates) for T, S, and T × S, respectively.
Table 4. The pseudobulb length (PL), pseudobulb short axis (PW), pseudobulb thickness (PT), inflorescence length (FL), number of pedicels (FB), floret numbers (FN), and days to flowering (FD) per plant at growth stage 3 (G3) were examined by analysis of variance for the effects of type of light source (T), supplemental light duration (S), and their interaction (T × S) on.
Table 4. The pseudobulb length (PL), pseudobulb short axis (PW), pseudobulb thickness (PT), inflorescence length (FL), number of pedicels (FB), floret numbers (FN), and days to flowering (FD) per plant at growth stage 3 (G3) were examined by analysis of variance for the effects of type of light source (T), supplemental light duration (S), and their interaction (T × S) on.
TraitMain and Interaction Effect
TST × S
F and p Values with Significance
FpFpFp
PL (mm)1.820.19 NS3.790.07 NS0.640.54 NS
PW (mm)0.110.89 NS23.860.00001 ****4.110.03 *
PT (mm)5.630.01 *14.500.0009 ***3.560.04 *
FL(cm)2.460.10 NS18.820.0001 ***3.370.04 *
FB9.270.0006 ***2.830.10 NS7.800.002 **
FN23.740.00001 ****0.420.52 NS2.190.13 NS
FD (day)10.930.0002 ***1.270.27 NS4.110.02 *
* p ≤ 0.05, ** p ≤ 0.01, *** p ≤ 0.001, **** p ≤ 0.0001, NS nonsignificant difference. n = 35, 15, and 105 plants (replicates) for T, S, and T × S, respectively.
Table 5. The pseudobulb length (PL), pseudobulb short axis (PW), pseudobulb thickness (PT), inflorescence length (FL), number of pedicels (FB), floret numbers (FN), and days to flowering (FD) per plant at growth stage 4 (G4) were examined by analysis of variance for the effects of type of light source (T), supplemental light duration (S), and their interaction (T × S).
Table 5. The pseudobulb length (PL), pseudobulb short axis (PW), pseudobulb thickness (PT), inflorescence length (FL), number of pedicels (FB), floret numbers (FN), and days to flowering (FD) per plant at growth stage 4 (G4) were examined by analysis of variance for the effects of type of light source (T), supplemental light duration (S), and their interaction (T × S).
TraitMain and Interaction Effect
TST × S
F and p Values with Significance
FpFpFp
PL (mm)0.170.84 NS0.370.55 NS0.740.49 NS
PW (mm)8.790.002 **1.270.27 NS0.300.74 NS
PT (mm)1.560.23 NS0.410.53 NS0.450.64 NS
FL(cm)1.610.22 NS2.290.14 NS6.010.009 **
FB7.280.004 **0.550.47 NS7.680.003 **
FN29.960.00001 ****1.410.25 NS24.350.00001 ****
FD (day)18.120.00001 ****13.090.002 **2.100.15 NS
** p ≤ 0.01, **** p ≤ 0.0001, NS non-significant difference. n = 35, 15, and 105 plants (replicates) for T, S, and T × S, respectively.
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Chang, C.-M.; Wang, C.-W.; Huang, M.-Y.; Chen, C.-I.; Lin, K.-H.; Shen, C.-P. The Effects of Light Treatments on Growth and Flowering Characteristics of Oncidesa Gower Ramsey ‘Honey Angel’ at Different Growth Stages. Agriculture 2023, 13, 1937. https://doi.org/10.3390/agriculture13101937

AMA Style

Chang C-M, Wang C-W, Huang M-Y, Chen C-I, Lin K-H, Shen C-P. The Effects of Light Treatments on Growth and Flowering Characteristics of Oncidesa Gower Ramsey ‘Honey Angel’ at Different Growth Stages. Agriculture. 2023; 13(10):1937. https://doi.org/10.3390/agriculture13101937

Chicago/Turabian Style

Chang, Chia-Man, Ching-Wen Wang, Meng-Yuan Huang, Chung-I Chen, Kuan-Hung Lin, and Chih-Pei Shen. 2023. "The Effects of Light Treatments on Growth and Flowering Characteristics of Oncidesa Gower Ramsey ‘Honey Angel’ at Different Growth Stages" Agriculture 13, no. 10: 1937. https://doi.org/10.3390/agriculture13101937

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