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Chun-Ho Pak and Chiwon W. Lee

Foliar micronutrient toxicity symptoms of Petunia hybrida `Ultra Crimson Star' were induced by elevated levels (from 0.25 to 6 mM) of boron (B), copper (Cu), iron (Fe), manganese (Mn), molybdenum (Mo) and zinc (Zn) in the nutrient solution. Foliar toxicity symptoms of most micronutrients (except Fe) were characterized by leaf yellowing, interveinal chlorosis, and marginal necrosis. Mo toxicity was most severe. Leaf abnormality was not induced by Fe in the concentration range tested. Visible foliar toxicity symptoms developed when nutrient solution contained 5.4, 32, 28, 24, and 16 mg· liter-1, respectively, of B, Cu, Mn, Mo and Zn. Biomass yield was reduced when the fertilizer solution contained (in mg· liter-1): 22 B, 64 Cu, 335 Fe, 28 Mn, 24 Mo, and 33 Zn.

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Chi Won Lee, Chun-Ho Pak, and Harrison G. Hughes

Stevia (Stevia rebaudiana Bert.) leaves produce stevioside and rebaudioside that can be used as a natural source of low-calorie sweetener which is heat-stable. Because of low fertility, this plant is often vegetatively propagated for field production. This study was conducted to optimize tissue culture procedures for propagating selected clones and explore the feasibility of producing the sweetener compounds by callus cultures. Shoot proliferation was best in Murashige and Skoog (MS) medium supplemented with 0.1 mg/l naphthaleneacetic acid (NAA) Plus 10 mg/l kinetin. Kinetin as a cytokinin source was better than benzyladenine (BA) especially when NAA was present. Callus production fronm leaf disc cultures was most prolific when a combination of 0.1 mg/l NAA and 3 mg/l BA was used in MS medium. The relative sweetener contents of callus cultures are currently being-analyzed.

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Chi Won Lee, Chun Ho Pak, and Jong Myung Choi

Micronutrient toxicity symptoms of seed geranium (Pelargonium × hortorum Bailey) `Ringo Scarlet' were experimentally induced by using 9 different concentrations of B, Cu, Fe, Mn, Mo and Zn in the fertilizer solution. Plants of 3-4 true leaf stage grown in peat-lite mix were constantly fed for 5 weeks with nutrient solutions containing 0.25, 0.5, 1, 2, 3, 4, 5, and 6 mM of each micronutrient. The control solution contained 20 uM B, 0.5 uM Cu, 10 uM Fe, 10 uM Mn, 0.5 uM Mo and 4 uM Zn. Visible foliar toxicity symptoms developed when the nutrient solution contained 2, 0.5, 5, 1, 0.25, and 0.5 mM, respectively, of B, Cu, Fe, Mn, Mo, and Zn. Reduction in dry matter yield was evident when 1 mM B, 2 mM Cu, 3 mM Fe, 2 mM Mn, 0.5 mM Mo, and 1 mM Zn were used in the fertilizer solution. Leaf chlorophyll contents decreased as Cu and Mn levels increased. Elevated levels of Fe increased tissue chlorophyll contents.

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Chun Ho Pak, Seung Won Kang, and Chiwon W. Lee

Efficacy of application methods and concentration of plant growth retardants on growth of chrysanthemum (Dendranthema ×grandiflorum cv. Cheasepeake) was tested. B-9 or cycocel (CCC) as a growth retardant was applied as drench or subapplication with nutrient solution. In the case of B-9 drench treatments, as B-9 concentrations increased, numbers of flowers and flower buds increased except in the 1500-ppm treatment. Increasing concentration of CCC also resulted in reduction of flower numbers, total plant height, total leaf area, branch number, and fresh weight. Reduction ratio of total plant height in 2000 ppm showed about 56.9% being compared to that of the 100-ppm drench treatment. B-9 or CCC, combined with nutrient solution, was also supplied from the C-channel subirrigation system. The B-9 subapplication treatment showed no significance among these concentrations, but flower numbers, total plant height, average plant height, and leaf numbers decreased as concentrations of CCC increased. B-9 or CCC with the same concentration was drenched after 2 weeks of the first experiment to compare planting time efficacy. Measured data increased until B-9 increased up to 2500 ppm and severe growth retardation resulted from the 5000-ppm treatment. Through this growth retardant application study, the combination of drenching concentration and period of plant growth regulators (PGRs) may result in effective growth retardation and reduction of application concentrations for pot plant production.

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Chiwon W. Lee, Chun-Ho Pak, and Jong-Myung Choi

Correlations between the nutrient solution concentration and tissue content of micronutrients were determined for geranium, marigold and petunia. When nutrient solution contained 0.25, 0.5, 1, 2, 3, 4, 5, 6 mM of boron (B), copper (Cu), iron (Fe), manganese (Mn), molybdenum (Mo) and zinc (Zn), the tissue content of each microelement increased linearly with increasing levels of the same micronutrient in the fertilizer. Equations for these correlations were established for the six micronutrients used for each species. Increasing levels of micronutrients did not influence tissue macroelement contents. Increasing levels of one micronutrient had little influence on the accumulation of other micronutrients in the tissue. Plant toxicity symptoms developed when the leaf content of microelements increased to a level 5-10 times that of plants grown with the control (Hoagland) solution.

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Chun Ho Pak*, Seung Won Kang, and Chiwon W. Lee

The influence of water-soluble fertilizer (WSF, 3 different formulations) and slow-release fertilizer (SRF, Osmocote, 14N-6.2P-11.6K) on the growth and quality of potted carnation (Dianthus caryophyllus cv. Invitation) in a C-channel mat irrigation system was investigated. When fertilized with 0.4, 0.8, or 2.0 g·L-1 of WSF (20N-7.9P-16.6K for weeks 1-4, 13K-0.1P-18.8K for weeks 5-11, and 15N-0P-12.5K for weeks 12-15), the 0.8 g·L-1 solution produced the highest quality plants as determined by total shoot fresh and dry weights, leaf area and number, plant height, and number of branches per pot. The quality of plants grown with 0.4 g·L-1 or 2.0 g·L-1 WSF solution was also commercially acceptable. The growth rate of all plants began to accelerate at around 60 days after treatment started, with some variation with the fertilizer treatments. Plants began to show a reduced growth rate at around 90 days from the treatment when they underwent a phase change from vegetative growth to reproductive growth. Plants grown with SRF alone were less vigorous than those grown with WSF, especially when temperature was lower. Results of this study indicate that high quality pot carnations can be produced, using a reduced amount of fertilizer applied to the C-channel mat irrigation system.

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Chiwon W. Lee, Jong-Myung Choi, and Chun-Ho Pak

Seed geranium (Pelargonium × hortorum) micronutrient toxicity symptoms were induced by applying elevated levels of B, Cu, Fe, Mn, Mo, and Zn in fertilizer solution. Beginning at the 3-4 true leaf stage, seedling plants established in 11-cm (0.67-liter) pots containing peat-lite growing medium were fertilized at each irrigation for 5 weeks with solutions containing 0.25, 0.5, 1, 2, 3, 4, 5, and 6 mm plus the standard concentration of each micronutrient. The standard solution contained 20 μm B, 0.5 μm Cu, 10 μm Fe, 10 μm Mn, 0.5 μm Mo, and 4 μm Zn. All treatment solutions contained a fixed level of macronutrients. Visible foliar toxicity symptoms were produced when the nutrient solution contained 0.5 mm B, 0.5 mm Cu, 5 mm Fe, 1 mm Mn, 0.25 mm Mo, or 0.5 mm Zn. Reduction in dry matter yield was evident when 1 mm B, 2 mm Cu, 3 mm Fe, 2 mm Mn, 0.5 mm Mo, or 1 mm Zn was used in the fertilizer solution. Leaf chlorophyll contents decreased as Cu and Mn levels in the concentration range tested increased. Elevated levels of Fe increased tissue chlorophyll contents. The relationship between the nutrient solution and tissue concentrations of each of the six micronutrients was determined.

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Sung Eun Lee, Chun Ho Pak, Yong Beom Lee, Harlene Hatterman-Valenti, and Chiwon W. Lee

Afield study evaluated the influence of planting density on the yield and quality of confectionery seed pumpkins grown near Hatton, N.D. An open-pollinated selection of Chinese snow-white seeds (CS) and a hull-less (HL) seed cultivar (`Takai', Johnny's Selected Seeds) were grown at three different planting densities (1-, 2-, or 3-ft plant spacing on rows 5 ft apart) from 5 May to 7 Oct. The total number of plants at high, medium, and low densities was 8712, 4356, and 2904 per acre (21,529, 10,764, and 7176 plants per ha, respectively). The average number of fruits harvested at high, medium, and low densities, respectively, was 0.93, 1.2, and 1.4 per plant for CS and 1.2, 1.7, and 2.5 per plant for HL. Total seed yields were estimated at 1011, 599, and 466 kg/acre (2498, 1480, and 1151 kg·ha-1) for CS and 661, 500, and 498 kg/acre (1633, 1235, and 1231 kg·ha-1) for HL, respectively, at high, medium, and low planting densities. While the average weight of fruits decreased as planting density increased, the total number and weight of seeds produced per fruit were unaffected by changing plant density in either cultivar.

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Yeun Joo Huh, Seoung Youl Choi, Hak Ki Shin, and Chun Ho Pak

Nonbranching chrysanthemums [Dendranthema × grandiflorum (Ramat.) Kitamura] are preferred because they require less labor in disbudding. High temperature is responsible for this phenotype of not having axillary buds or poor lateral shoot development. This study attempted to find out the effect of temperature and identify the involvement of endogenous polyamine contents in axillary bud formation of nonbranching chrysanthemum cv. Iwanohakusen. Plants were treated at 22, 26, 30, 34, and 38 °C for 9 hours midday for 2 months. Polyamine content [putrescine (Put), spermidine (Spd), spermine (Spm)] was analyzed 1 month after treatment and axillary buds were counted when the flowers opened. Results revealed that viable axillary buds decreased remarkably at 30 and 34°C. It was also found out that not only low temperature, but also the excessively high temperature of 38 °C induced axillary bud formation. Exposure to 38 °C increased the Put contents and resulted in high Put/(Spd + Spm) ratio as 22 °C, 26 °C. Temperature of 30, 34 °C lowered Put/(Spd + Spm) ratio. Results further showed that not polyamine contents, but polyamine ratio (Put/Spd + Spm) or transformation of Put to Spd and Spm may be involved in the axillary bud formation in nonbranching chrysanthemum.

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Jongyun Kim, Seung Won Kang, Chun Ho Pak, and Mi Seon Kim

Variegated foliage plants are often used in interiorscaping in low light environments. The changes in leaf morphology and coloration of two variegated foliage plants, english ivy (Hedera helix ‘Golden Ingot’) and polka dot plant (Hypoestes phyllostachya), under various light intensities [photosynthetic photon flux (PPF) at 2.7, 6.75, 13.5, 67.5, and 135 μmol·m−2·s−1] were investigated to elucidate their optimum indoor light environment. Digital image analysis was used to quantify the changes in variegation area and color in CIELAB color space. The changes in leaf morphology (thickness, length:width) and coloration were different between the two species. In general, growth of both species increased with increasing PPF. English ivy showed no significant changes in leaf variegation under different PPF. Under low PPF (≤13.5 μmol·m−2·s−1), newly developed leaves of polka dot plant had reduced leaf variegation (44%, 72%, and 85% variegation loss under 13.5, 6.75, and 2.7 μmol·m−2·s−1, respectively). Anthocyanin content in leaves of polka dot plant also decreased with decreasing PPF, which reduced plants’ aesthetic quality. English ivy leaves under high PPF (≥67.5 μmol·m−2·s−1) displayed high brightness (L*) and yellowish green color (hue angle < 108°), which diminished its aesthetic value. Smaller leaf size and narrower shape of polka dot plant leaves under high PPF (≥67.5 μmol·m−2·s−1) also diminished its aesthetic value. Overall, english ivy performed well in a PPF range from 2.7 to 13.5 μmol·m−2·s−1, and polka dot plant required a PPF of at least 13.5 μmol·m−2·s−1 to maintain its red-purple variegation in the indoor environment.