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  • Author or Editor: Nihal C. Rajapakse x
  • Journal of the American Society for Horticultural Science x
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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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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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Low-temperature storage potential of rooted cuttings of garden chrysanthemum [Dendranthema ×grandiflorum (Ramat.) Kitamura] cultivars and its relationship with carbohydrate reserves were evaluated. Storage of chrysanthemum cuttings at -1 and -3 °C resulted in freezing damage. Visual quality of rooted cuttings stored at 0 or 3 °C varied among cultivars. Quality of `Emily' and `Naomi' cuttings was reduced within a week by dark storage at 0 or 3 °C due to leaf necrosis, while `Anna' and `Debonair' cuttings could be held for 4 to 6 weeks without significant quality loss. In `Anna' and `Debonair', low-temperature storage reduced the number of days from planting to anthesis regardless of storage duration. However, flowers of plants grown from stored cuttings were smaller than those of nonstored cuttings. At the beginning of storage, `Emily' and `Naomi' had lower sucrose, glucose, and fructose (soluble sugars) content compared to `Anna' and `Debonair'. Regardless of temperature, leaf soluble sugar was significantly reduced by dark storage for 4 weeks. In stems, sucrose and glucose were reduced while fructose generally increased during low-temperature storage probably due to the breakdown of fructans. Depletion of soluble sugars and a fructan-containing substance during low-temperature dark storage was greater in `Emily' and `Naomi' than in `Anna' and `Debonair'. Low irradiance [about 10 μmol·m-2·s-1 photosynthetically active radiation (PAR) from cool-white fluorescent lamps] in storage greatly improved overall quality and delayed the development of leaf necrosis in `Naomi'. Cuttings stored under light were darker green and had a higher chlorophyll content. Leaf and stem dry weights increased in plants stored under medium and high (25 to 35 μmol·m-2·s-1 PAR) irradiance while no change in dry weight was observed under dark or low light. Results suggest that the low-temperature storage potential of chrysanthemum cultivars varies considerably, and provision of light is beneficial in delaying the development of leaf necrosis and maintaining quality of cultivars with short storage life at low temperatures.

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The effects of carbon dioxide enrichment on growth, photosynthesis, and postharvest characteristics of `Meijikatar' potted roses were determined. Plants were grown in 350, 700, or 1050 μl CO2/liter until they reached 50% flower bud coloration and then were placed into dark storage for 5 days at 4 or 16C. Plants grown in 700 or 1050 μl CO2/liter reached the harvest stage earlier and were taller at harvest than plants produced in 350 μl CO2/liter, but there were no differences in the number of flowers and flower buds per plant among CO2 treatments. Plants grown in early spring were taller and had more flowers and flower buds than plants grown in late winter. Shoot and root growth of plants grown in 700 or 1050 μl CO2/liter were higher than in plants produced in 350 μl CO2/liter, with plants grown in early spring showing greater increases than plants grown in late winter. Immediately after storage, plants grown in 350 μl CO2/liter and stored at 4C had the fewest etiolated shoots, while plants grown in 1050 μl CO2/liter and stored at 16C had the most. Five days after removal from storage, chlorophyll concentration of upper and lower leaves had been reduced by ≈50% from the day of harvest. Carbon dioxide enrichment had no effect on postharvest leaf chlorosis, but plants grown in early spring and stored at 16C had the most leaf chlorosis while plants grown in late winter and stored at 4C had the least leaf chlorosis.

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Abstract

Potted foliage and floricultural species were evaluated for transpiration rates under low-light conditions. Environmental conditions during the experiment were 25° ± 2°C, 75% ± 10% RH, and 20 μmol·s−1 ·m−2 (400−700 nm) light intensity. Leaf cuticular and stomatal morphology were characterized with scanning electron micrographs. Coleus had the highest transpiration rate, Chrysanthemum was intermediate, and Ficus, Peperomia, and Epipremnum had the lowest transpiration rates. Abscisic acid (ABA) treatment reduced the daytime transpiration, which eliminated the diurnal fluctuation of transpiration in all species but had no effect on night transpiration, except in Coleus. Assuming complete stomatal closure at night with ABA treatment, cuticular transpiration accounts for 43% to 80% of the total transpiration rate under low-light conditions. This result points to the importance of leaf cuticular and stomatal characteristics in controlling water use of plants under low light or dark-storage. Species differed in cuticular characteristics, stomatal frequency and size, and leaf area. Stomatal frequency correlated well with transpiration rates, except in those species with unique stomatal morphologies, such as Ficus, with sunken stomates surrounded by a protruding ridge. Coleus and Chrysanthemum developed less epicuticular wax than the other species. Epicuticular and stomatal characteristics were correlated with transpiration rates of these species.

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Plants grown in far red (FR) light deficient environments are typically shorter because of short internodes, resembling plants treated with GA biosynthesis inhibitors. The role of GAs in the reduction of stem elongation of `Bright Golden Anne' chrysanthemum [Dendranthem ×grandiflora (Ramat.) Kitam. (syn. Chrysanthemum ×morifolium Ramat.)] grown in FR light deficient (-FR) environment was investigated by following the response of chrysanthemums grown in - FR environment to exogenous application of GA1, GA19, or GA20, and the metabolism of GA12 and GA19 in -FR or +FR environment. FR light deficient environment resulted in 25% to 30% shorter plants than in +FR environment. Final height of GA1- and GA20-treated plants followed a quadratic pattern while that of GA19 treated plants followed a linear pattern as the dosage increased from 0 to 50 μg/apex. The response to GA1 was the greatest followed by GA20 and GA19, regardless of the light environment. Application of GA1 (50 μg/apex) increased final height by 65% compared with no GA (0 μg/apex) application under either +FR or -FR light environment, suggesting the response to GA1, which is the active form, remained the same. Responses to GA19 and GA20 declined under -FR light. [14 C]GA12 and [14C]GA19 metabolized slowly in the -FR environment suggesting that the turnover of GAs may have caused in part the lower response to GA19. Although metabolism of GA1 under -FR environments was not investigated, observations with GA1 application experiments support that -FR environment may have enhanced inactivation of GA1. Chemical name used: gibberellic acid (GA).

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Growth chambers constructed of photoselective plastic films were used to investigate light quality effects on flowering and stem elongation of six flowering plant species under strongly inductive and weakly inductive photoperiods. Three films were used: a clear control film, a far red (FR) light absorbing (AFR) film and a red (R) light absorbing (AR) film. The AFR and AR films intercepted FR (700 to 800 nm) and R (600 to 700 nm) wavelengths with maximum interception at 730 and 690 nm, respectively. The phytochrome photoequilibrium estimates of transmitted light for the control, AFR, and AR films were 0.71, 0.77, and 0.67. The broad band R:FR ratios were 1.05, 1.51, and 0.77, respectively. The photosynthetic photon flux was adjusted with neutral density filters to provide similar light transmission among chambers. Zinnia elegans Jacq., Dendranthema×grandiflorum Kitam. (chrysanthemum), Cosmos bipinnatus Cav., and Petunia×hybrida Vilm.-Andr. plants grown under the AFR film were shorter than control plants. The AFR film had no effect on height of Antirrhinum majus L. (snapdragon) or Rosa×hybrida (miniature rose). Anthesis of zinnia, chrysanthemum, cosmos (short-day plants), and miniature rose (day-neutral plant) was not influenced by the AFR films. Anthesis of petunia and snapdragon (long-day plants) was delayed up to 13 days by AFR films under weakly inductive photoperiods. In petunia, initiation and development of floral structures were not affected by the AFR films during strongly inductive photoperiods. However, during weakly inductive photoperiods, initiation of the floral primordia was significantly delayed and overall development of the floral meristem was slower than control plants indicating that the AFR films could increase the production time if long-day plants were produced off-season. Daylength extension with electric light sources could overcome this delay in anthesis yet achieve the benefit of AFR films for height reduction without the use of chemical growth regulators.

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Steady-state oxygen diffusion in flesh of apples (Malus domestics Borkh. cvs. Braeburn and Cox's Orange Pippin), Asian pears (Pyrus serotina Rehder. cvs. Hosui and Kosui), and nectarines [Prunus persica (L.) Batsch. cvs. Red Gold and Sunglo] was studied using a nondestructive method at 20C. Fruit flesh was found to exert a significant resistance to O2 diffusion resulting in measurable O2 gradients between tissues immediately beneath the skin and those at the fruit center for all these fruits. The magnitude of these O2 gradients varied between crops and cultivars and depended on the respiration rate and on effective O2 diffusivity in fruit flesh (De). Values of Dc varied with the cultivar and were broadly consistent with intercellular space volume. The range of De values obtained suggested that 02 diffusion in fruit flesh takes place in a combination of series and parallel modes in the intercellular space and fluid/solid matrix of the flesh. The results imply that O2 diffusivity in flesh tissues must be taken into consideration in the determination of critical external O2 level in controlled/modified atmosphere (CA/MA) storage.

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Responses to selected chemical growth retardants (daminozide, paclobutrazol, and prohexadione-Ca) and GA1 and GA3 under photoselective greenhouse covers with various phytochrome photoequilibrium estimates (φe) were evaluated using `Bright Golden Anne' chrysanthemum [Dendranthema ×grandiflora Kitam. (syn. Chrysanthemum morifolium Ramat.)] as the model plant to better understand the height control mechanism by far red (FR) light depleted environments. Plant height linearly decreased as φe increased from 0.72 to 0.83. The rate of height decrease of daminozide treated plants was less than that of water (control) or GA3-treated plants. The rate of height reduction was not different between control and GA3-treated plants among chambers with various φe. Both paclobutrazol and prohexadione-Ca reduced plant height regardless of φe, but the height reduction by paclobutrazol was more than that by prohexadioneCa. The combination of paclobutrazol and prohexadione-Ca reduced plant height more than either alone. GA1 reversed the height reduction caused by paclobutrazol and prohexadione-Ca regardless of φe, but the height increase by GA1 was more when it was applied with prohexadione-Ca than when applied alone. Results show that photoselective covers with high φe were effective in controlling height of chrysanthemums without chemical growth retardants. The linear relationship between plant height and φe suggests that effectiveness of photoselective covers increased as φe increased. The photosynthetic photon flux (PPF) transmission of photoselective covers decreased as the φe increased because of the increasing dye concentration. Identifying photoselective covers that effectively filter out FR light from sunlight and reduce plant height while minimizing the PPF reduction is critical for commercial success of photoselective covers. Gibberellins are, at least partially, involved in height control by photoselective covers. Photoselective greenhouse covers did not reduce responsiveness to gibberellins, and it appears that the mechanism may be to suppress gibberellin biosynthesis. Results also suggest that increased metabolism of GA1 to GA8 was not the mechanism of height control by photoselective covers. Chemical names used: butanedioic acid mono (2,2-dimethylhydrazide) [daminozide]; (±)-(R*,R*)-b-((4-chlorophenyl)methyl)-a-(1,1-dimethylethyl)-1H-1,2,4-triazole-1-ethanol [paclobutrazol]; 3,5-dioxo-4-(1-oxopropyl)cyclohexanecarboxylic acid [prohexadione-Ca]; gibberellic acid [GA].

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