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Effects of Light Intensity, Spectral Composition, and Paclobutrazol on the Morphology, Physiology, and Growth of Petunia, Geranium, Pansy, and Dianthus Ornamental Transplants

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Cristian E. Collado at North Carolina State University
Cristian E. Collado
Ricardo Hernández at North Carolina State University
Ricardo Hernández
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Abstract and Figures

Under light-limiting conditions, many ornamental greenhouse-grown plants show undesired morphological characteristics, such as plant elongation (hypocotyl and epicotyl length) and low dry mass, which reduce plant quality. Research has shown that use of plant growth regulators (PGRs) and changes in both light intensity and spectral composition can reduce these undesired characteristics. However, little is known about the role of the combined effects of supplemental lighting and PGRs on the production of ornamental seedlings. The objective of this study was to characterize the combined and independent effects of light intensity, spectral composition, and PGR applications on the greenhouse production of ornamental transplants. Petunia (Petunia × hybrida), geranium (Pelargonium × hortorum), pansy (Viola × wittrockiana) and dianthus (Dianthus chinensis) were grown for 32–42 days under three supplemental light (SL) treatments: 1) high-pressure sodium (HPS), 2) light-emitting diodes (LEDs) with a 6 blue (B):5 green (G):89 red (R) (percent photon flux ratio), and 3) LEDs with 19B:81R (100 μmol m−2 s−1, 18 h photoperiod for all treatments). A control (No SL) was also included. In addition, a portion of plants were also sprayed with the paclobutrazol PGR (PBZ and No PBZ). The synergistic effects of the combination of PBZ and supplemental lighting resulted in the most compact plants, caused by a reduction in plant height by PBZ and an increase in dry mass by SL. However, PBZ reduced shoot dry mass of most plant species and light combinations. Plant compactness was greater under the 6B:5G:89R LED composition for petunia and when combined with PBZ for geranium than for plants under HPS lighting. Root dry mass of petunia, geranium, and pansy plants increased in response to SL compared with no SL by 2.4–5.7-fold. Results from the two LED spectra were unexpected; plants under 6B:5G:89R were more compact (petunia, geranium), had higher anthocyanin concentrations (petunia), were shorter (petunia, pansy, dianthus) and had less leaf area (petunia, pansy, dianthus) than plants in the SL treatment with a higher B and lower G PF (19B:81R). Supplemental lighting and PBZ can be used in conjunction or independently to improve plant morphology. The increased light from SL provided the most benefits by improving dry mass, compactness, and leaf number for most plant species. However, when PBZ was used in combination with SL, plant compactness increased for some species. The spectral composition of SL had an impact on plant growth and morphology, warranting additional research on plant responses to small changes in the spectral composition of SL.
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Journal of Plant Growth Regulation (2022) 41:461–478
https://doi.org/10.1007/s00344-021-10306-5
Effects ofLight Intensity, Spectral Composition, andPaclobutrazol
ontheMorphology, Physiology, andGrowth ofPetunia, Geranium,
Pansy, andDianthus Ornamental Transplants
CristianE.Collado1· RicardoHernández1
Received: 7 July 2020 / Accepted: 4 January 2021 / Published online: 22 February 2021
© The Author(s), under exclusive licence to Springer Science+Business Media, LLC part of Springer Nature 2021
Abstract
Under light-limiting conditions, many ornamental greenhouse-grown plants show undesired morphological characteristics,
such as plant elongation (hypocotyl and epicotyl length) and low dry mass, which reduce plant quality. Research has shown
that use of plant growth regulators (PGRs) and changes in both light intensity and spectral composition can reduce these
undesired characteristics. However, little is known about the role of the combined effects of supplemental lighting and
PGRs on the production of ornamental seedlings. The objective of this study was to characterize the combined and inde-
pendent effects of light intensity, spectral composition, and PGR applications on the greenhouse production of ornamental
transplants. Petunia (Petunia × hybrida), geranium (Pelargonium × hortorum), pansy (Viola × wittrockiana) and dianthus
(Dianthus chinensis) were grown for 32–42days under three supplemental light (SL) treatments: 1) high-pressure sodium
(HPS), 2) light-emitting diodes (LEDs) with a 6 blue (B):5 green (G):89 red (R) (percent photon flux ratio), and 3) LEDs
with 19B:81R (100μmolm−2s−1, 18h photoperiod for all treatments). A control (No SL) was also included. In addition, a
portion of plants were also sprayed with the paclobutrazol PGR (PBZ and No PBZ). The synergistic effects of the combina-
tion of PBZ and supplemental lighting resulted in the most compact plants, caused by a reduction in plant height by PBZ and
an increase in dry mass by SL. However, PBZ reduced shoot dry mass of most plant species and light combinations. Plant
compactness was greater under the 6B:5G:89R LED composition for petunia and when combined with PBZ for geranium
than for plants under HPS lighting. Root dry mass of petunia, geranium, and pansy plants increased in response to SL com-
pared with no SL by 2.4–5.7-fold. Results from the two LED spectra were unexpected; plants under 6B:5G:89R were more
compact (petunia, geranium), had higher anthocyanin concentrations (petunia), were shorter (petunia, pansy, dianthus) and
had less leaf area (petunia, pansy, dianthus) than plants in the SL treatment with a higher B and lower G PF (19B:81R). Sup-
plemental lighting and PBZ can be used in conjunction or independently to improve plant morphology. The increased light
from SL provided the most benefits by improving dry mass, compactness, and leaf number for most plant species. However,
when PBZ was used in combination with SL, plant compactness increased for some species. The spectral composition of
SL had an impact on plant growth and morphology, warranting additional research on plant responses to small changes in
the spectral composition of SL.
Keywords Light-emitting diode· Plant growth regulators· PBZ· HPS· Supplemental light· Daily light integral· PPFD·
Blue light· Green light· Red light
Introduction
Plant growth regulators (PGRs) affect the balance of natu-
rally synthesized plant hormones. Most common PGRs
are exogenous hormones (naturally occurring or synthetic
analogs) that inhibit the biosynthesis and translocation
of endogenous hormones or block hormone receptors
(Rademacher 2015). The main groups of endogenous plant
hormones include auxins, gibberellins, cytokinins, abscisic
Handling Editor: Scott Finlayson.
* Ricardo Hernández
ricardo_hernandez@ncsu.edu
1 Department ofHorticultural Sciences, NC State University,
Raleigh, NC, USA
Content courtesy of Springer Nature, terms of use apply. Rights reserved.
... Hazar and Bora (2018) stated that different doses of paclobutrazol in fuchsia (Fuchsia spp.) reduced the number of leaves, Berova and Zlatev (2000) stated that paclobutrazol applied to tomatoes caused a decrease of up to 5% in the number of leaves. Collado and Hernández (2021) reported that paclobutrazol applied to petunia and dianthus species reduced leaf numbers by 7% and 6%, respectively; however, they reported that geranium and pansy plants had no effect on the number of leaves. In our study, the effects of the applied doses on the number of leaves per plant varied according to the genotype. ...
... The dose increases of paclobutrazol applied to G2 decreased the seedling biomass (Table 3). For the petunia, pansy, geranium and clove plant species, paclobutrazol was significantly reduced plant dry mass (Collado and Hernández, 2021). Ruter (1994) stated that shoot dry weight, root dry weight and total biomass (shoot dry weight + root dry weight) decreased as the amount of paclobutrazol applied to the Pyracantha coccinea increased. ...
... This decrease can be explained by increasing doses of paclobutrazol, as the biosynthesis of the gibberellin hormone was suppressed and resulted in smaller leaf areas. According to the results of previous studies, paclobutrazol applications significantly reduced leaf area of petunia, geranium, pansy and clove plants when compared to seedlings without paclobutrazol application (Collado and Hernández, 2021). Bahlebi et al. (2017) have found a 26-29% reduction in leaf area of potted geranium (Pelargonium spp.) plants in response to paclobutrazol (100 mg L -1 ) application. ...
Determining of the effects of paclobutrazol treatments on seedling height control of wild Gypsophila bicolor (Freyn & Sint.) Grossh
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... Different colors of shading nets have different shading effects on different plants, and there is no unified conclusion. Pansy (Viola × wittrockiana) is a greenhouse crop often grown under black shade nets ranging from 50 to 80% shading (Collado and Hernández 2022) . Black shading nets are commonly used to protect agricultural crops from excessive solar radiation and wind and to conserve water (Chang et al. 2016;Collado and Hernández 2022) . ...
... Pansy (Viola × wittrockiana) is a greenhouse crop often grown under black shade nets ranging from 50 to 80% shading (Collado and Hernández 2022) . Black shading nets are commonly used to protect agricultural crops from excessive solar radiation and wind and to conserve water (Chang et al. 2016;Collado and Hernández 2022) . Apply four shading levels (0%, 50%, 75%, and 95% shade) using black mesh to Jeffersonia dubia revealed that moderate light (50% shading) is recommended for cultivating J. dubia without physiological defects (Rhie et al. 2014). ...
... Different colors of shading nets have different shading effects on different plants (Chang et al. 2016;Rhie et al. 2014;Zha et al. 2022;Zhang et al. 2022), and there is no unified conclusion. Black shading nets are commonly used to protect agricultural crops from excessive solar radiation and wind and to conserve water (Chang et al. 2016;Collado and Hernández 2022) . Hence, this study aims to explore the impact of black shading meshes on the fruit quality of different blueberry cultivars. ...
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Blueberry fruit is famous for its anthocyanin abundance and has high nutritional, medicinal, and economic value. The adaptability of different source cultivars to high temperature in summer has not been systematically explored. The objective of this study was to evaluate the suitability of different blueberry cultivars under different shading environments and explore the effects of different shading intensities on fruit quality and antioxidant substances. In this study, three cultivars respectively belonging to three types (rabbiteye, southern highbush, and northern highbush) of blueberries were shaded, and the fruit size, shape, hardness, nutritional quality index, and antioxidant substances were determined. The results show that excessive shading affects flower bud differentiation, leading to abnormal flowering and fruiting of the blueberry cultivar ‘Chandler’. The fruit firmness of highbush blueberries (‘Primadonna’ and ‘Chandler’) in the one-layer black shading (T1) group was significantly higher than that in the total light (CK) group. Total phenols, flavonoids, anthocyanins, and protein reached the highest values in the T1 treatment for cultivar ‘Brightwell’. Moreover, the malondialdehyde and H2O2 contents and peroxidase activity in the T1 group were significantly lower than those in the two-layer black shading (T2) group, but the catalase and polyphenol oxidase activities in the T1 group were significantly higher than those in the T2 group. There was a correlation between the main antioxidant substances, and different blueberry cultivars had different tolerances to shading. This study provides a practical reference for improving fruit quality and the efficient utilization of antioxidant substances in blueberry production.
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... Light is the main energy source-driver of photosynthesis. Light intensity is the pivotal determinant of plant growth and performance [16][17][18] . Production of crops in greenhouses and controlled environments has nowadays attracted a lot of attention 19 . ...
... Production of crops in greenhouses and controlled environments has nowadays attracted a lot of attention 19 . ere is a need to optimize the photosynthetic photon ux density (PPFD) needed for plant growth in an approach with the highest resource use eciency 6,18 . TiO 2 nanoparticles are used to improvemeyield during winter cultivation of plants 20 . ...
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Due to the photocatalytic property of titanium dioxide (TiO2), its application may be dependent on the growing light environment. In this study, radish plants were cultivated under four light intensities (75, 150, 300, and 600 μmol m⁻² s⁻¹ photosynthetic photon flux density, PPFD), and were weekly sprayed (three times in total) with TiO2 nanoparticles at different concentrations (0, 50, and 100 μmol L⁻¹). Based on the obtained results, plants used two contrasting strategies depending on the growing PPFD. In the first strategy, as a result of exposure to high PPFD, plants limited their leaf area and send the biomass towards the underground parts to limit light-absorbing surface area, which was confirmed by thicker leaves (lower specific leaf area). TiO2 further improved the allocation of biomass to the underground parts when plants were exposed to higher PPFDs. In the second strategy, plants dissipated the absorbed light energy into the heat (NPQ) to protect the photosynthetic apparatus from high energy input due to carbohydrate and carotenoid accumulation as a result of exposure to higher PPFDs or TiO2 concentrations. TiO2 nanoparticle application up-regulated photosynthetic functionality under low, while down-regulated it under high PPFD. The best light use efficiency was noted at 300 m⁻² s⁻¹ PPFD, while TiO2 nanoparticle spray stimulated light use efficiency at 75 m⁻² s⁻¹ PPFD. In conclusion, TiO2 nanoparticle spray promotes plant growth and productivity, and this response is magnified as cultivation light intensity becomes limited.
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... The most common approach involves the use of plant growth regulators that inhibit gibberellin, a plant hormone responsible for stem elongation (Guleria et al., 2021). Several gibberellin inhibitors are used in floriculture, such as Placobutrazol, Daminozide, and Uniconazole, with effective results in restricting the growth of various ornamental species, such as chrysanthemums, poinsettias, petunias, begonias, carnations, lilies, and gladioli, producing more compact plants with shorter stems and smaller leaves (Aljaser and Anderson, 2021;Collado and Hernández, 2022). ...
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... Consequently, this led to an augmentation in the proportion of blue and red wavelengths relative to other spectrums within the greenhouse solar spectrum. It is noteworthy that differences in the spectral composition of electrical lighting can significantly impact plant physiology, morphology, and growth in growth chambers (Spalholz et al., 2020) and under conditions of low sunlight, 3-5 mol m -2 d -1 (Hernańdez and Kubota, 2014;Collado and Hernańdez, 2022). ...
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The expanding cannabis production sector faces economic challenges, intensified by freshwater scarcity in the main US production areas. Greenhouse cultivation harnesses sunlight to reduce production costs, yet the impact of greenhouse light levels on crucial production components, such as plant growth, branching, and water use efficiency (WUE), remains poorly understood. This study aimed to assess the effects of combined sunlight and supplemental lighting on the crop’s main production components and leaf gas exchange of Cannabis sativa ‘Suver Haze’ in the vegetative stage. Within a greenhouse, LED lighting provided at intensities of ~150, 300, 500, and 700 µmol m⁻² s⁻¹ (18-hour photoperiod), combined with solar radiation, resulted in average daily light integrals of 17.9, 29.8, 39.5, and 51.8 mol m⁻² d⁻¹. Increasing light levels linearly increased biomass, leaf area, and the number of branches per plant and square meter, with respective rates of 0.26 g, 32.5 cm², and 0.41 branches per mole of additional light. As anticipated, crop evapotranspiration increased by 1.8-fold with the increase in light intensity yet crop WUE improved by 1.6-fold when comparing the lowest and highest light treatments. Moreover, water requirements per unit of plant biomass decreased from 0.37 to 0.24 liters per gram when lighting increased from ~18 to 52 mol m⁻² d⁻¹, marking a 35% reduction in evapotranspiration. These results were supported by increments in leaf photosynthesis and WUE with light enhancement. Furthermore, our findings indicate that even 52 mol m⁻² d⁻¹ of supplemental lighting did not saturate any of the crop responses to light and can be economically viable for cannabis nurseries. In conclusion, light supplementation strongly enhanced photosynthesis and plant growth while increasing WUE. Additionally, a comprehensive discussion highlights the shared physiological mechanisms governing WUE in diverse plant species and their potential for water conservation under enhanced lighting conditions.
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... During these months the Photosynthetic Photon Flux Density (PPFD) level is far from adequate and as light being the energy source promoting photosynthesis and growth in plants it follows that under low PPFD the other environmental factors cannot be utilized efficiently (Adegoroye and Jolliffe 1987, Schrader 2011, Collado and Hernández 2022. ...
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... Thus, pansy plants are often grown under black shade net ranging from 50% to 80% shading (Collado and Hern andez 2022). The use of plant growth regulators (PGRs) in pansy production is also common to reduce stretching under the lower light levels (Collado and Hern andez 2022;Kessler and Behe 1998). ...
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Pansy (Viola ×wittrockiana) is a greenhouse crop commonly grown under black shade net; it often requires the use of chemical plant growth regulators to maintain a compact growth habit. Nonchemical efforts to alter plant morphology, such as height, would provide a more sustainable solution than chemical application. The objective of these studies was to evaluate the effects of different colors of shade nets on controlling growth and flowering of pansy. In Expt. 1, 'Clear Yellow', 'Buttered Popcorn', and 'Deep Orange' pansy plugs were placed under 30% blue or black shade net or, as a control group, where grown with no shade net. In Expt. 2, the same three cultivars of pansy were grown under 50% black, red, pearl, or aluminized shade net. Data were collected on plant height, plant width, flower number, plant survival, soil plant analysis development chlorophyll meter (SPAD) readings, and light quality. In Expt. 1, the blue shade net reduced height to flower and height to leaves, but also decreased flower number and plant survival as compared with black shade net. All plants under no shade died. In Expt. 2, SPAD, an indicator of plant quality by estimating leaf greenness, was found to be lower under black shade net, whereas pearl shade net led to a decrease in plant height and no effect on the number of flowers. Light quality, including red-to-far-red ratio, varied among shade treatments, whereas light intensity was reduced under aluminized, black (50%), and red shade nets compared with other shade treatments. Blue and pearl shade nets both reduced plant height, but blue shade net also reduced plant survival and flowering.
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... Another instance of B-mediated stem elongation was published by Zou [45], who found that marigold 'P-4' (Tagetes erecta) grown under sole-source lighting providing 180 µmol·m −2 ·s −1 of B radiation for 12 h·d −1 was up to 54% taller than those grown under 180 µmol·m −2 ·s −1 of R radiation for the same duration. It was also found that petunia and dianthus seedlings grown under SL emitting 19% B radiation for 16 h·d −1 were 59% and 3% taller, respectively, than those grown under SL emitting 6% B radiation [47]. However, the former SL treatment included 5% G radiation, which may have antagonized B-mediated stem compaction compared to the latter treatment, which did not contain G radiation. ...
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In commercial interior green walls, plant trimming and replacement necessitated by stem elongation under low interior light levels is labor intensive and costly. Antigibberellin plant growth regulators (PGRs) may slow stem elongation and thus reduce maintenance costs in this environment. In Expt. 1, two PGRs were applied as foliar spray or drench to three spiderwort selections [two of zebra plant ( Tradescantia zebrina ) and one of inch plant ( Tradescantia fluminensis )] immediately before installation in a green wall, each at three rates: ancymidol (ANC) foliar spray at 25, 100, and 200 mg·L ⁻¹ ; paclobutrazol (PBZ) foliar spray at 20, 80, and 160 mg·L ⁻¹ ; and PBZ drench at 1, 4, and 8 mg·L ⁻¹ , along with an untreated control. In Expt. 2, 80 mg·L ⁻¹ PBZ foliar spray, 1 mg·L ⁻¹ PBZ applied via subirrigation four times, and the combination of these two treatments, was evaluated on ‘Burgundy’ zebra plant. In both experiments, plants were placed in a vertical modular tray interior green wall. Change in total stem and specific internode length were measured every 14 days after installation for 3 months to calculate growth per month. Antigibberellin application slowed internode elongation of spiderwort selections during the first month after installation. Antigibberellins were more effective in zebra plant at reducing overall stem growth rate and less so on inch plant. Across the three spiderwort selections, 25 mg·L ⁻¹ foliar spray of ANC resulted in no difference in growth rate when compared with the control, although 100 to 200 mg·L ⁻¹ foliar spray was effective. Based on the results of both experiments, moderate and high rates of PBZ, applied both as a foliar spray and drench, resulted in similar reduction in stem elongation. PBZ applied as 20 to 80 mg·L ⁻¹ foliar spray, 4 mg·L ⁻¹ drench before installation in the wall, or a combination of an 80 mg·L ⁻¹ PBZ pre-installation foliar spray and recurring 1 mg·L ⁻¹ via subirrigation (four times) were effective at growth suppression of spiderworts for at least 3 months. Even rates of PBZ of 160 mg·L ⁻¹ foliar spray or 8 mg·L ⁻¹ drench did not show phytotoxicity in treated plants and could be considered for use. We recommend a pre-installation application of 80 mg·L ⁻¹ foliar spray or 4 mg·L ⁻¹ drench for controlling stem growth across spiderwort selections. Application of antigibberellin PGRs to plants before installation in green walls slows stem growth and can contribute to reduced maintenance costs.
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Adding green [G (500–600 nm)] radiation to blue [B (400–500 nm)] and red [R (600–700 nm)] radiation creates white radiation and improves crop inspection at indoor farms. Although G radiation can drive photosynthesis and elicit the shade-avoidance response, its effects on plant growth and morphology have been inconsistent. We postulated G radiation would counter the suppression of crop growth and promotion of secondary metabolism by B radiation depending on the B photon flux density ( PFD ). Lettuce ( Lactuca sativa ‘Rouxai’) was grown in a growth room under nine sole-source light-emitting diode (LED) treatments with a 20-hour photoperiod or in a greenhouse. At the same photosynthetic photon flux density [ PPFD (400–700 nm)] of 180 μmol·m ⁻² ·s ⁻¹ , plants were grown under warm-white LEDs or increasing B PFD s at 0, 20, 60, and 100 μmol·m ⁻² ·s ⁻¹ with or without substituting the remaining R radiation with 60 μmol·m ⁻² ·s ⁻¹ of G radiation. Biomass and leaf expansion were negatively correlated with the B PFD with or without G radiation. For example, increasing the B PFD decreased fresh and dry mass by up to 63% and 54%, respectively. The inclusion of G radiation did not affect shoot dry mass at 0 or 20 μmol·m ⁻² ·s ⁻¹ of B radiation, but it decreased it at 60 or 100 μmol·m ⁻² ·s ⁻¹ of B radiation. Results suggest that the shade-avoidance response is strongly elicited by low B radiation and repressed by high B radiation, rendering G radiation ineffective at controlling morphology. Moreover, substituting R radiation with G radiation likely reduced the quantum yield. Otherwise, G radiation barely influenced morphology, foliage coloration, essential nutrients, or sensory attributes regardless of the B PFD . Increasing the B PFD increased red foliage coloration and the concentrations of several macronutrients (e.g., nitrogen and magnesium) and micronutrients (e.g., zinc and copper). Consumers preferred plants grown under sole-source lighting over those grown in the greenhouse, which were more bitter and less acceptable, flavorful, and sweet. We concluded that lettuce phenotypes are primarily controlled by B radiation and that G radiation maintains or suppresses lettuce growth depending on the B PFD .
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  • Nov 2016
  • SCI HORTIC-AMSTERDAM
Lamp spectral customization can be a strategy to achieve desirable plant characteristics when plants are grown under sole-source electric lighting. Vegetable transplants can be efficiently and economically grown under indoor-production systems with electrical lighting; however, species-specific light recipes have to be developed to improve plant growth, development and morphology, as well as to reduce electrical consumption. The objective of this study was to evaluate the growth and morphology of tomato transplants to a broad range of blue to red (B:R) photon flux (PF) ratios under LEDs and cool white fluorescent lamps (CWF). Tomato ‘Komeett’ and ‘Beaufort’ seedlings were grown in a climate control growth chamber. Using LEDs, seven light treatments with different blue (B), green (G) and red (R) PF ratios were used: 100R, 10B:90R, 20B:28G:52R, 30B:70R, 50B:50R, 75B:25R and 100B. In addition, a CWF treatment served as the control. Hypocotyl length of ‘Komeett’ decreased with the increase of percent B PF up to 75% B. Plant leaf area was 64–72% greater under treatments emitting both B and R PF than in the 100 B and 100 R treatments. Similarly, tomato ‘Komeett’ fresh mass, dry mass, leaf number and chlorophyll concentration was comparable among the treatments containing B and R PF and greater than in 100 B and 100 R treatments. However, plant compactness in the 30B:70R treatment was 42% greater than in the 10B:90R treatment. Anthocyanin concentration increased with the increase of percent B PF up to 75% B. Also, plants in 30B:70R and 50B:50R had 39% and 36% greater dry mass than in CWF, respectively. In addition, 30B:70R and 50B:50R LEDs had 172% greater growing efficacy (g k Wh⁻¹) than high output fluorescent lamps. The addition of G light did not have any effects on tomato physiological responses. ‘Beaufort’ plant morphology and growth were severely affected by intumescences development and intumescence severity decreased under higher percentages of B PF. In summary, 30B:70R, 50B:50R were the best spectrums to produce tomato seedlings under LEDs tested here; however, plant quality under CWF, 10B:90R, 20B:28G:52R, and 75B:25R was also acceptable.
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Impact of sun-simulated white light and varied blue:red spectrums on the growth, morphology, development, and phytochemical content of green- and red-leaf lettuce at different growth stages
Article
  • Feb 2020
  • SCI HORTIC-AMSTERDAM
Light drives photosynthesis and regulates plant morphology, physiology, and phytochemical content. Using light emitting diodes (LEDs), customized spectra can be created, including spectrum that simulates solar light. The aim of this study was to assess the growth, development, and phytochemical content at three marketable stages of lettuce (transplant, baby-leaf, and head-lettuce) under a sun-simulated spectrum and common light spectra used in indoor growing systems. Oakleaf red (Salanova® 'Red Oakleaf') and green (Salanova® 'Green Oakleaf') lettuce were grown under seven spectra. A sun-simulated light treatment (SUN) was created with 5 % ultraviolet-A (UV-A), 20 % blue (B), 26 % green (G), 26 % red (R), and 23 % far-red (FR) light as percent photon flux density (PFD). In addition, five treatments of differing blue:red (B:R) ratios were evaluated: 0B:100R (100R), 20B:80R, 50B:50R, 80B:20R, and 100B:0R (100B) and fluorescent white light was used as a control (6500 K). Plants were provided with 200 ± 0.7 μmol·m −2 ·s −1 biologically active radiation (300-800 nm) for 18 h and grown at 20.0 ± 0.2 °C temperature. Fresh mass of lettuce in the SUN treatment was not significantly different when compared to B:R light treatments in all harvest dates despite the 36 % greater photosynthetic photon flux density (PPFD) in B:R treatments. Plant dry mass on day 17 of' Green Oakleaf' and 'Red Oakleaf' grown under 20B:80R was 15-39 % greater than those grown in 100B and SUN. When calculating total dry mass accumulation to cumulative yield photon flux density (YPFD), plants in SUN treatment accumulated the same dry mass per YPFD input (mg mol −1). Leaf area at day 42 of plants in 100B, SUN, and FL was 39-78 % greater than plants in B:R treatments. At final harvest (day 42), plant stem length in SUN was 2.1-4.4 times longer than in all other treatments, indicating bolting and flowering initiation. Both total phenolic and anthocyanin concentrations were greater in the B:R treatments than in SUN, 100R, and 100B treatments. This study presents baseline information for lettuce responses under LED-simulated SUN spectrum when compared to common B:R treatments and offers insights on lettuce growth and morphology under different spectra at multiple growth stages.
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Physiological, biochemical, antioxidant and growth characterizations of gibberellin and paclobutrazol-treated sweet leaf (Stevia rebaudiana B.) herb
Article
  • Oct 2017
A greenhouse experiment was designed to study the responses of Stevia rebaudiana herb to paclobutrazol (PBZ) and gibberellin (GA) treatments. GA and PBZ treatments caused no significant impact on photosynthesis pigments while they increased carbohydrates, amino acids and protein metabolites. Stevia showed a potent antioxidant activity through scavenging DPPH, NO·; O2·− and OH· radicals which was highlighted in GA and PBZ treatments. The enzymatic and non-enzymatic antioxidant system of Stevia plant showed a significant increase in response to PBZ and GA treatments. PBZ treatment decreased plant growth while GA treatment had no significant effect on it. Collectively, both GA and PBZ treatments effectively increased metabolites and antioxidant property of Stevia herb.
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Spectral Effects of Supplemental Greenhouse Radiation on Growth and Flowering of Annual Bedding Plants and Vegetable Transplants
Article
  • Sep 2017
Supplemental radiation (SR), traditionally provided by high-pressure sodium (HPS) lamps, is recommended for greenhouse production of seedlings during radiation-limiting conditions. Light-emitting diodes (LEDs) have emerged as an appealing alternative to HPS lamps primarily because they can provide SR at improved energy efficiencies, they have longer fixture lifetimes, and the radiation spectrum can be tailored to potentially manipulate plant morphology by targeting radiation absorption of specific photoreceptors. We grew seedlings of three annual bedding plants and two vegetable transplants in greenhouses at 20 °C under a 16-h photoperiod under six SR treatments: five that delivered a photosynthetic photon flux density (PPFD) of 90 μmol·m⁻²·s–1 from HPS lamps (HPS90) or LEDs [four treatments composed of blue (B; 400–500 nm), red (R; 600–700 nm), far red (FR; 700–800 nm), and/or white LEDs] and one that delivered 10 μmol·m⁻²·s–1 from HPS (HPS10) lamps as a control with matching photoperiod. The LED treatments, defined by the percentages of B, green (G; 500–600 nm), and R radiation, were B10R90, B45R55, B10G5R85, and B12G20R68 + FR (FR at 12 μmol·m⁻²·s–1). At transplant, leaf area and seedling height were similar among 90 μmol·m⁻²·s–1 treatments in all species except snapdragon (Antirrhinum majus), in which seedlings grown under B12G20R68 + FR had 62% greater leaf area than those grown under B45R55 and were 47%, 18%, 38%, and 62% taller than those grown under HPS90, B10R90, B10G5R85, and B45R55, respectively. After transplant and finishing under the same SR treatments, snapdragon flowered on average 7 days earlier under the B12G20R68 + FR treatment than the other LED treatments, whereas geranium (Pelargonium ×hortorum) grown under B45R55 and B12G20R68 + FR flowered 7 to 9 days earlier than those under the B10G5R85 and B10R90 treatments. Seedlings of each species grown under the HPS10 treatment accumulated less dry weight and took longer to flower compared with seedlings under the other SR treatments. We conclude that radiation quality of SR has relatively little effect on seedling growth and subsequent flowering although in some crops, flowering may be earlier when SR includes FR radiation. © 2017, American Society for Horticultural Science. All rights reserved.
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Rose-scented Geranium ( Pelargonium spp.) Plant Growth, and Essential Oil Yield and Composition as Affected by Paclobutrazol Application
Article
  • Jul 2017
Rose-scented geranium oil is extracted from the shoots (mostly the leaves) of the Pelargonium spp. through steam- or hydro-distillation. To extract less than 0.2% oil, farmers must transport and distil bulky herbage. This makes geranium oil production costly, and high time- and energy-consuming process. To investigate the effect of different paclobutrazol (PBZ) concentrations (0, 100, 200, 300 mg/L of water) on vegetative growth, and oil yield and composition of rose-scented geranium, three pot experiments were conducted. The experiments were conducted in a glasshouse of the University of Fort Hare, Alice, South Africa (located at 25°45′S and 28°16′E, an altitude of 520 m above sea level), between Oct. 2011 and May 2013. The treatments were arranged in a randomized complete block design (RCBD) in four replications. The PBZ was sprayed on the plants at 1 month of regrowth stage. Chlorophyll content increased with concentration of PBZ. The reduction of plant height in all PBZ-treated plants was significant, ranged between 18% and 33%. Plant canopy also reduced by 5% to 23%, and the differences were more noticeable in the plants grown between January and May (summer/autumn season), producing compact plants. Leaf area and internode length reduced as PBZ concentration increased. Paclobutrazol had no significant effect on leaf number, and essential oil yield and composition. This implies that, through applying PBZ, compacted (less bulky) rose-scented geranium could be produced without significant change in essential oil yield per plant and essential oil composition. © 2017, American Society for Horticultural Science. All rights reserved.
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Growth and Subsequent Yield of Tomatoes following End-of-day Light Treatment of Transplants
Article
  • Dec 1991
The influence of end-of-day (EOD) light treatments of tomato (Lycopersicon esculentum Mill. cv. Mountain Pride) transplants on growth and subsequent fruit production was investigated. In the first experiment, transplants were treated with EOD red (R) and far-red (FR) light for 2 weeks in a controlled environment and then placed in the greenhouse under ambient light conditions from November to March. Before transplanting to the greenhouse, transplants treated with EOD R light were shorter and had less total leaf length than plants that were not treated with EOD light (controls). EOD R light increased the number of flowers on the plants before first harvest but had no effect on subsequent fruit production (as compared to plants treated with EOD FR light or control plants). In the second experiment, cool-white fluorescent lights (a light source high in red wavebands) were used to supplement solar light that transplants received in a nonshaded glasshouse for 1 hour before the end of the natural photoperiod. The fluorescent light reduced transplant height and total leaf length as compared to plants not treated with supplemental light. Supplemental fluorescent light for transplants had no effect on subsequent fruit production in the field. These results suggest that EOD light treatments that affect tomato transplant growth do not affect subsequent fruit production.
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Highly efficient detection of paclobutrazol in environmental water and soil samples by time-resolved fluoroimmunoassay
Article
  • Jun 2016
A fast and ultrasensitive indirect competitive time-resolved fluoroimmunoassay (TRFIA) was developed for the analysis of paclobutrazol in environmental water and soil samples. Paclobutrazol hapten was synthesized and conjugated to bovine serum albumin (BSA) for producing polyclonal antibodies. Under optimal conditions, the 50% inhibitory concentration (IC50 value) and limit of detection (LOD, IC20 value) were 1.09μgL(-1) and 0.067μgL(-1), respectively. The LOD of TRFIA was improved 30-fold compared to the already reported ELISA. There was almost no cross-reactivity of the antibody with the other structural analogues of triazole compounds, indicating that the antibody had high specificity. The average recoveries from spiked samples were in the range from 80.2% to 104.7% with a relative standard deviation of 1.0-9.5%. The TRFIA results for the real samples were in good agreement with that obtained by high-performance liquid chromatography analyses. The results indicate that the established TRFIA has potential application for screening paclobutrazol in environmental samples.
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