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  • Author or Editor: Nihal C. Rajapakse x
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Growth and development responses of three chrysanthemum [Dendranthema ×grandiflora (Ramat.) Kitam. (syn. Chrysanthemum ×morifolium Ramat.)] cultivars (`Bright Golden Anne', `Iridon', and `Yellow Snowdon') to photoselective plastic films with varying concentrations (0 to 0.22 g·m-2) of a far-red (FR) light absorbing dye were investigated under greenhouse conditions. Photoselective films reduced stem elongation of all three cultivars. The greater the dye concentration in the film, the greater and earlier the reduction in stem elongation. After 4 weeks, `Yellow Snowden', `Bright Golden Anne', and `Iridon' plants grown under the film with the highest dye concentration (Afr3 film) were 21%, 26%, and 26% shorter than control plants, respectively. Height reduction under photoselective films was caused by shorter internodes. Photoselective covers were most effective in reducing the stem elongation during the early vegetative period. Following transition to the reproductive stage, weekly stem elongation rates were reduced. At the time of flowering, `Yellow Snowden', `Bright Golden Anne', and `Iridon' plants grown under the film with the highest dye concentration (Afr3 film) were 12%, 7%, and 14% short9er than control plants, respectively. Photoselective covers did not affect the anthesis of chrysanthemum cultivars, but resulted in a 10% to 14% reduction in flower diameter depending on the cultivar. Although the films with higher dye concentration were more effective in reducing stem elongation of chrysanthemum, increased dye concentration reduced light transmission. Thus, photoselective covers that reduce light transmission over 25% would not be suitable for commercial production.

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Growth chambers constructed from photoselective plastic films were used to investigate the effects of light quality on height manipulation and flowering of photoperiodic plant species. Three types of treatment films were used; control, a far-red light intercepting film (YXE-10) and a red light intercepting film (SXE-4). The red (600-700 nm):far-red (700-800 nm) ratios and phytochrome photoequilibrium estimates for the control, YXE-10 and SXE-4 films were 1.0 and 0.71, 1.5 and 0.77, and 0.71 and 0.67, respectively. The photosynthetic photon flux was adjusted to uniformity among chambers using neutral density filters. Spectral filters did not effect minimum and maximum air temperatures. Experiments were conducted using quantitative long day (Antirrhinum majus and Petunia × hybrida), quantitative short day (Zinnia elegans and Dendranthema × grandiflorum) and day-neutral (Rosa × hydrida) plant species under natural short-day conditions. Plants produced under the YXE-10 filters were significantly shorter than the control plants, while plants produced under the SXE-4 films had similar or increased height compared to the control plants. However, both height response and flowering times varied with the crop species. Flowering time of Rosa × hybrida plants was uniform among all treatments. Flowering of quantitative long-day plants was delayed by at least 10 days under the YXE-10 film and was most responsive to the filtered light. Flowering of quantitative short-day plants was delayed by 2 days under the YXE-10. Days to flower for plants produced under the SXE-4 film were similar to the control plants for all species tested.

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A research collaboration between Clemson Univ. and Mitsui Chemicals, Japan, has been established to develop and test photoselective greenhouse covers that can filter out far-red (FR) light and control plant height with minimal use of chemicals. The effects of polymethyl methacylate (PMMA) filters containing FR-intercepting dyes were evaluated on watermelon, pepper, chrysanthemum, and tomato to select an optimum dye concentration. As the dye concentration increased, FR interception increased, photosynthetic photon flux (PPF) decreased, and phytochrome photoequilibrium increased from 0.72 to 0.82. Light transmitted through photoselective filters reduced plant height effectively in all species tested. However, watermelon was the most responsive (50% height reduction) and chrysanthemum was the least responsive (20% height reduction) to filtered light. Tomato and peppers had an intermediate response. In watermelons, total shoot dry weight was reduced over 25% compared to the control plants, with a progressive decrease in shoot weight as the dye concentration increased. The specific stem dry weight was gradually reduced as the dye concentration increased. Specific leaf dry weight was slightly reduced under filters, suggesting that smaller plants as opposed to a reduction in dry matter production primarily caused total dry weight reduction. Light transmitted through filters reduced percentage dry matter accumulation into stems from 27% to 18% and increased dry matter accumulation into leaves from 73% to 82%. Photoselective filters are effective in controlling height similarly to chemical growth regulators. Considering the PAR reduction by increase in dye concentration, a dye concentration that gives a light reduction of 25% or 35% may be optimum for commercial development of photoselective films.

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`Green Duke' broccoli plantlets, which were ready for transplanting after 2 weeks of photoautotrophic (sugar free) culture under the conditions of 1100 μmol·mol–l CO2 (outside the vessel), 22 + 4C air temperature, and 140 μmol·m–2·s–1 photosynthetic photon flux (PPF), were stored for 6 weeks at 5C in darkness or in white, red, or blue light at 2 μmol·m–2·s–l PPF (light compensation point at 5C). Photoperiod was set at 24 hour/day during storage. Spectral quality significantly affected plantlet quality: stem length was longer and chlorophyll concentration of leaves was lower in red or in blue light than in white light or in darkness after 6 weeks in storage. Regardless of the spectral quality, light in storage maintained plantlet dry weight at a level comparable to that before storage; dry weight was reduced significantly in dark-stored plantlets. Spectral quality did not significantly affect the photosynthetic and regrowth potential of plantlets. All plantlets stored in light, regardless of light spectra, grew preferably and had similar dry weight and stem length after 9 weeks of transplanting to the greenhouse under natural light.

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Endogenous gibberellins of chrysanthemum [Dendranthema ×grandiflorum (Ramat)] cv. Bright Golden Anne were characterized in apices from plants grown 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 GA1 and GA19 standards were detected in fractions using the recently-developed non-dwarf rice bioassay. Di-deuterated 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. In a preliminary quantification study, GA20 and GA1 levels were found to be higher in apices from plants grown under control filters while GA19 levels were higher in apices grown under CuSO4 filters. The possibility that light transmitted through CuSO4 filters alters gibberellin levels in shoot apices is discussed.

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Broccoli (Brassica oleracea L. Botrytis Group `Green Duke') and Hosta tokudama F. Maekawa `Newberry Gold' plantlets, which were ready for transplanting after photoautotrophic (sugar-free) culture, were stored 4 to 6 weeks at 5C under various light qualities and photosynthetic photon fluxes (PPF). Illumination during storage maintained quality, photosynthetic ability, and regrowth potential of plantlets stored at low temperature. PPF affected quality of broccoli and Hosta plantlets. Broccoli plantlets responded to storage light quality, while Hosta did not. White light maintained the quality of broccoli plantlets better during 6 weeks of storage than did red or blue light. Red and blue light caused an increase in internode length and reduction in chlorophyll concentrations compared to white light. Photosynthetic and regrowth potentials of plantlets were not affected by spectral quality during storage. Considering changes in dry weight, stem length, and leaf yellowing, the quality of broccoli plantlets was best maintained under white light at 2 μmol·m–2·s–1 PPF. PPF and light quality were shown to be important factors in the preservation of transplant quality and suppression of growth of the plantlets during low-temperature storage.

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The response of `Bright Golden Anne' and `Spears' chrysanthemum plants to EOD-R or FR light was evaluated to determine the involvement of phytochrome in regulation of plant morphology under CuSO4 filters. Light transmitted through the CuSO4 filter significantly reduced height, internode length and stem dry weight of `BGA' and `Spears' chrysanthemum plants. However, the degree of response varied with the cultivar. Exposure to EOD-FR reversed the reduction of plant height, internode length and the stem dry weight caused by the light transmitted through CuSO4 filters to a level comparable with control plants. Exposure to EOD-FR did not significantly alter height and stem dry weight under control filter Exposure to EOD-R light reduced the height and stem dry weight of `BGA' plants grown under control filter but EOD-R had no effect under CuSO4 filters. In `Spears' plants, EOD-R caused stem dry weight reduction under control filters, but did not reduce stem or internode elongation. The results suggest phytochrome may be involved in controlling plant response under CuSO4 filters. However, there are evidence to indicate that an additional mechanism may be acting on stem/internode elongation.

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Recent medical interest in plant antioxidants in human health has stimulated the interest in functional phytochemicals of fruits and vegetables. Numerous reports link antioxidant capacity of phytochemicals to the reduction of degenerative diseases. As a result, sales of herbal antioxidant supplements have increased tremendously although negative (or no) effects have been documented with certain supplements. There are many interactive reactions among phytochemicals. At this point, our understanding of interactions among phytochemicals is limited. Therefore, medical professionals are reluctant to prescribe supplements as a mean to boost antioxidants, but they agree that consumption of fresh fruits and vegetables is essential for a healthy life and provides a better alternative than supplements to boost antioxidant uptake. Carotenoids are receiving attention because of their pro-vitamin A activity and antioxidant properties. Two of the widely investigated carotenoids for improvement are lycopene and β-carotene. Genetic composition, cultural practices, environmental conditions, and processing can all affect carotenoid profiles. Light has been shown to affect carotenoids and we are investigating if changing the spectral composition in the growing environment can alter carotenoid levels. Preliminary results show that tomatoes grown under a high red light environment have increased lycopene and overall carotenoid contents. Nutritionally enhanced produce will benefit both growers and consumers.

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The influence of 3 temperatures (1, 10 and 25°C). 9 combinations of initial O2 (5, 10 and 20%) and CO2 (0, 10 and 20%) concentrations, and 3 storage durations at 1°C (2, 13 and 24 days) on the O2 consumption of `Red Gold' nectarines was investigated. Fruits were sealed in glass jars, flushed with respective gas mixtures and stored in dark incubators maintained at 1, 10 or 25°C. Head space O2 concentration was monitored at selected intervals until it dropped down to 1% or less. The oxygen consumption rate decreased significantly with decrease in temperature and initial O2 concentration. The O2 consumption rate increased as storage duration increased. The range of initial CO2 concentrations used in this study had no effect on O2 consumption rate. An empirical model was developed to estimate O2 consumption rate of `Red Gold' nectarines as a function of temperature, initial O2 and CO2 concentrations and storage duration.

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Experiments were conducted to evaluate Dendranthema × grandiflorum (Ramat.) Kitamura cv. Bright Golden Anne quality and post-storage growth following storage in the range of 5 to 35C, initial soil water levels (60%, 80%, 100%), and durations (0 to 8 days). Transpiration rate showed a quadratic relationship with storage temperature. Initial soil water content had little effect on transpiration rate in dark storage environments. The lowest transpiration rate was observed in plants stored at 15 or 20C. Amino acid (AA) leakage and post-storage growth were well-correlated. Plants stored at or above 25C became etiolated during storage, while storage at 15C or below did not cause etiolation. Temperatures at or below 15C did not affect subsequent growth rate of chrysanthemum plants. Storage at 20C and above caused a reduction in post-storage growth rate following 2 days of storage.

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