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  • Author or Editor: Nihal C. Rajapakse x
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The interaction of light quality and growing season on growth and carbohydrate metabolism of chrysanthemum was evaluated using 6% CuSO4 and water as spectral filters. Light transmitted through the CuSO4 filter significantly reduced plant height and internode length compared to control plants regardless of the season. Light transmitted through CuSO4 filters delayed flowering. Total number of flowers was not affected but plants grown under CuSO4 filter had smaller flowers than those grown under the control filter. Light transmitted through CuSO4 filter reduced leaf and stem soluble sugar and starch concentrations regardless of the growing season. However, me magnitude of reduction was greater in spring than in fall-grown plants. Stems of fall-grown plants had mom starch deposition than spring-grown plants under both filters. The reduction of leaf and stem carbohydrate content (per organ basis) was greater than that of concentrations due to reduced stem elongation and total dry matter accumulation. Filters with specific spectral characteristics can be used as alternative means of controlling height and producing compact plants in the greenhouses regardless of the growing season. However, flowering should be evaluated with individual flower crops as flowering response may interact with the quality of light and growing season.

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The use of light quality as an alternate method for controlling ornamental plant growth was evaluated using copper sulfate solutions as optical filters, The light passed through CuSO4 solutions had high red/far-red (R/FR) ratio. Plant height and average internode length were significantly reduced by high R/FR light. Plants grown under high R/FR light had smaller leaves and a lower total leaf area but had thicker leaves, as indicated by specific leaf weight, than the control plants. Fresh and dry weights of leaves, stems and roots were reduced by high R/FR light. Dry matter accumulation in leaves was increased by high R/FR light while it was reduced in stems. Exogenous gibberellic acid (GA) application partially overcame the height reduction under high R/FR light indicating that GA biosynthesis maybe affected by light treatment. Results suggests alteration of light quality could be used in controlling ornamental plant growth as an alternate method to conventional chemical growth regulator applications.

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Endogenous gibberellins of chrysanthemum [Dendrathema×grandiflorum (Ramat) cv. Bright Golden Anne] were characterized in preparation for quantification of endogenous gibberellins in apices under control and CuSO4 spectral filters. Expanding shoots were separated into young expanding leaves and apices. Methanolic extracts of young expanding leaves were purified by solvent partitioning, PVPP column chromatography, and reversed-phase high performance liquid chromatography. Two bioactive regions corresponding to the HPLC retention times of GA and GA19 standards were detected in fractions using the recently developed non-dwarf rice bioassay. Dideuterated internal standards of GA12, GA53, GA19, GA20, and GA1 were added to similar extracts of shoot apices. The presence of endogenous GA53, GA19, GA20, and GA1 in chrysanthemum apices was confirmed by isotope dilution using gas chromatography–mass spectrometry-selected ion monitoring and Kovats retention indices. Ions for the deuterated internal standard of GA12 were detected, but not for endogenous GA12. The above results demonstrate that the early 13-hydroxylation pathway operates in chrysanthemum.

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Plant response to photoselective plastic films with varying spectral transmission properties was tested using lisianthus (Eustoma grandiflorum) `Florida Pink', `Florida Blue', and `Florida Sky Blue'. Films were designated YXE-10 (far-red light-absorbing film) and SXE-4 (red light absorbing film). Light transmitted through YXE-10 films reduced plant height compared to control plants by 10% (`Florida Blue'), and stem dry weight by 19% to 40%, but the response varied by cultivar. Internode length was reduced by 10% to 19% when `Florida Pink' and `Florida Sky Blue' plants were grown under YXE-10 films. Leaf and root dry weights were not affected by YXE-10 films, with the exception that `Florida Sky Blue' plants had a lower leaf dry weight than the control plants. Light transmitted through SXE-4 films increased plant height of `Florida Pink' plants by 15% but not of `Florida Blue' or `Florida Sky Blue.' Regardless of cultivar, dry weight of leaf, stem and root tissue was not affected by SXE-4 films as compared to control films. The average number of days to flower and bud number were not affected by YXE-10 or SXE-4 films, regardless of cultivar. The results suggest that selective reduction of far-red wavelengths from sunlight may be an alternative technique for greenhouse production of compact plants, but the magnitude of the response is cultivar specific.

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The interactions of light quality and growing season on growth and carbohydrate content of chrysanthemum [Dendranthema × grandiflorum (Ramat.) Kitamura] plants were evaluated using 6% CuSO4 and water (control) as spectral filters. Light transmitted through the CuSO4 filter significantly reduced plant height and internode length compared to control plants regardless of the season. However, the degree of response varied with growing season. Light transmitted through CuSO4 filters delayed flowering. Total number of flowers was not affected by spectral filter, but plants grown under CuSO4 filter had smaller flowers than those grown under the control filter. Light transmitted through CuSO4 filter resulted in reduced leaf and stem soluble sugar (sucrose, glucose, and fructose) and starch concentrations regardless of the growing season. However, the magnitude of reduction was greater in spring- than in fall-grown plants. Stems of fall-grown plants had more starch deposition than spring-grown plants under both filters. Filters with specific spectral characteristics can be used as alternative means of producing compact plants in the greenhouses, however, the delay in flowering and smaller flowers could limit their use for growth control of plants intended for flower production.

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The role of light quality and quantity in regulating growth of vegetative Dendranthema × grandiflorum (Ramat.) Kitamura was evaluated using CuSO4 solutions and water (control) as spectral filters. Copper sulfate filters increased the red (R): far-red (FR) and the blue (B): R ratios (R = 600 to 700 nm; FR = 700 to 800 nm; B = 400 to 500 urn) of transmitted light. Photosynthetic photon flux (PPF) under 4%, 8% and 16% CuSO4 filters was reduced 26%, 36%, and 47%, respectively, from natural irradiance in the greenhouse, which averaged ≈ 950 μmol·m-2·s-1. Control treatments were shaded with Saran plastic film to ensure equal PPF as the corresponding C uSO4 chamber. Average daily maxima and minima were 26 ± 3C and 16 ± 2C. At the end of the 4-week experimental period, average height and internode length of plants grown under CuSO4 filters were ≈ 40% and 34% shorter than those of plants grown under control filter. Reduction in plant height and internode length was apparent within 1 week after the beginning of treatment. Total leaf area (LA) was reduced by 32% and leaf size (LS) was reduced by 24% under CuSO4 filters. Specific leaf weight (SLW) was higher under CuSO4 filters than for the controls. Irradiance transmitted through CuSO4 filters reduced fresh and dry leaf weights by 30%. Fresh and dry stem weights of plants grown under CuSO4 filters were 60% lower than those of controls. Relative dry matter accumulation into leaves was increased in plants grown under CuSO4 filters while it was reduced in stems. A single application of GA3 before irradiation partially overcame the height reduction under CuSO4 filters, suggesting GA biosynthesis/action may be affected by light quality. Our results imply that alteration of light quality could be used to control chrysanthemum growth as an alternative method to conventional control by chemical growth regulators. Chemical names used: gibberellic acid (GA)

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Growth chamber experiments were conducted to investigate the effectiveness of several photoselective plastic films in controlling height of `Sweet Success' cucumber, `Mt. Pride' tomato, and `Capistrano' bell pepper transplants. Four types of treatment films; a control, two far-red light intercepting films (YXE-1 and YXE-10), and a red light intercepting film (SXE-1), with R: FR ratios of 1.0, 2.0, 1.6, and 0.8, respectively, were used as the covering materials of experimental chambers. Photosynthetic photon flux (PPF) was adjusted to be the same in all chambers with cheese cloth. Treatment period for cucumber and tomato was 15 days and that for bell pepper was 20 days. At the end of the treatment, significantly shorter plants were found in both YXE-1 and YXE-10 chambers for all the three tested crops. However, YXE-10 was more effective than YXE-1 in producing compact cucumber, tomato and bell pepper transplants. SXE-4 film produced taller plants than control film. Magnitude of response to filtered light varied with the crop species. Number of leaves was not significantly affected by the light transmitted through photoselective filters, indicating that the height reduction was mainly caused by the reduction in internode length. With the commercial development of photoselective greenhouse covers or shade material in the near future, nursery and greenhouse industry could potentially reduce the cost for growth regulating chemicals, reduce the health risks to their workers and consumers, and reduce environmental pollution.

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The far-red light intercepting photoselective plastic greenhouse covers have been shown to be effective in producing compact vegetable transplants. However, photoselective films reduce the photosynthetic photon flux (PPF) transmission compared to conventional plastic films because of the dye contained in the film. The low PPF in greenhouses covered with photoselective films may result in decreased plant dry matter production and could especially be a problem in the season with low light level and in northern latitudes. Therefore, this study was conducted to determine if covering at the end of the day (EOD) with photoselective films was effective in controlling height of vegetable seedlings. This will allow growers to maintain a high light level during daytime for optimum growth of plants. Cucumber seedlings were exposed to light transmitted through a photoselective film and a clear control film. Three exposure durations: continuous, exposure to filtered light from 3:00 pm to 9:00 am, and from 5:00 pm - 9:00 am, were evaluated. Results show that, after 15 days of treatment, about 25% of height reduction could be achieved by exposing the plants at the EOD from 3:00 pm to 9:00 am or from 5:00 pm to 9:00 am. Plants grown continuously under filtered light were the shortest. Compared to plants grown in photoselective chamber continuously, EOD exposed plants had greater leaf, stem and shoot dry weights, greater leaf area and thicker stem. Specific leaf and stem dry weights were also greater in EOD exposed plants. Number of leaves was not significantly affected by any exposure periods tested. The results suggested that the EOD use of photoselective film is effective in reducing height of cucumber seedlings. The responses of other crops need to be evaluated to test the feasibility of using photoselective film as a EOD cover on wide range of crops.

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Abstract

Experiments were conducted to determine the effect of pre-treatments with abscisic acid (ABA), silver thiosulfate (STS), or ethylene on transpiration rate of Chrysanthemum morifolium L. cv. Bright Golden Anne during the dark. ABA and STS reduced subsequent dark transpiration, while exposure to ethylene increased it. Treatment with STS partially reduced the influence of ethylene. These results indicate the possibility of using pre-treatments to reduce water loss under dark shipping/storage conditions.

Open Access

Hosta (Hosta tokudama Makeawa `Newberry Gold') plantlets were micropropagated photoautotrophically (without sucrose in medium) or photomixotrophically (with 2% sucrose in medium) for 3 weeks at 23 °C under 80 μmol·m-2·s-1 photosynthetic photon flux (PPF) prior to long-term storage. Plantlets were stored for 4, 8, or 12 weeks at 5, 10, or 22 °C in darkness or under white (400-800 nm), blue (400-500 nm), or red (600-700 nm) light at or near light compensation points. Illumination during storage was necessary to maintain dry weight and regrowth potentials of plantlets in vitro, but light quality had no effect on these parameters. All photoautotrophic plantlets stored in darkness were of poor quality at the time of removal from storage and died when transferred to the greenhouse. Dark-stored photomixotrophic plantlets survived storage for 12 weeks at 5 °C, but declined in appearance (visual quality) as the storage duration increased. Decline in visual quality was greater when plantlets were stored at 10 and 22 °C. Leaf dry weight of illuminated plantlets increased and percentage of leaf yellowing decreased as storage temperature increased. Recovery of illuminated plantlets from photomixotrophic storage was best when plantlets were stored at 22 °C. These plantlets were characterized by increased visual quality (color and form) and increased dry weight compared with those in other treatments. After 60 days in the greenhouse, the dry weight of these plantlets was similar for 4-, 8-, and 12-week storage durations, indicating flexibility in storage time if specific light and temperature provisions are met.

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