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Hyeon-Hye Kim and Kiyoshi Ohkawa

As a new product in the floricultural market, Zephyra elegans D. Don, shows great potential. It is a new product, so there is little known about its physiology. In this study, the growth cycles and the effects of day/night temperatures on flowering control of this new product were investigated. Stems elongated gradually during the growing season but more slowly after flowering. Original corm fresh weight decreased with increasing daughter corm fresh weight. Druing the growing season, the original corm dies after producing usually one daughter corm. The high ambient temperature of summer adversely effected shoot emergence. The optimum day/night temperature regimes for shoot emergence was 15/10 °C and for growth and flowering it was 20/15 °C. Under these conditions, it is possible to produce Zephyra elegans D. Don year-round.

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Hyeon-Hye Kim, Changhoo Chun, Toyoki Kozai and Junya Fuse

Spinach (Spinacia oleracea L.) was chosen to demonstrate that value-added transplant can be relatively easily produced under artificial light in a closed system. Transplant production under artificial light was divided into three periods, and the photoperiod during each period was varied. It was found that the rate of floral development could be controlled by photoperiod treatments, although floral initiation itself could not be manipulated. Short photoperiod treatments retarded floral development and stem elongation. This occurred even when the transplants were transferred for transplanting to natural conditions with long days and high temperatures. In conclusion, by providing the short photoperiod during the transplant production process, marketable plants with negligible bolting can be produced under natural long-day conditions. Moreover, the production cost per transplant in summer could be reduced by using a combination of natural and artificial lighting during the transplant production process. These results open the possibility to produce value-added transplants of different species under artificial lighting conditions and control their floral development and/or stem elongation for a timely and profitable harvest.

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Hyeon-Hye Kim, Changhoo Chun, Toyoki Kozai and Junya Fuse

Spinach (Spinacia oleracea L.) was chosen to demonstrate that the respective vegetative or reproductive conditions of transplants can be controlled in their early stages of development under artificial light in a closed system. Transplant production under artificial light was divided into three growth phases and the photoperiod during each of these phases was varied. The rate of floral development was controlled by photoperiod, but floral initiation itself was not affected. Short photoperiod treatments (8 or 12 hours/day) retarded floral development and stem elongation (bolting). This delay continued even after the transplants were transferred to natural long-day (15.5 hours/day on average) conditions with high temperatures (17 and 37 °C minimum and maximum). We concluded that by using short photoperiods during transplant production, marketable plants with reduced bolting could be produced under natural long-day conditions. In Japan, spinach with this rosetting capacity would be of greater value. Further, this concept opens the possibility of producing better quality transplants of several species under artificial lighting conditions of appropriate length, and thereby controlling their floral development and/or bolting.

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Kiyoshi Ohkawa, Hyeon-Hye Kim, Emiko Nitta and Yukinori Fukazawa

Leucocoryne, a native to Chile, has violet, blue, or white flowers and is increasing in popularity as a cut flower. The effects of storage temperature and duration on flower bud development, shoot emergence, and anthesis were investigated. Bulbs stored at 20 to 30 °C for 22 weeks produced 3.4 flower stems per bulb between March and April. Bulbs stored at 20 °C flowered earliest, followed by those stored at 25 °C. Bulbs stored at 30 °C flowered last. After 16 weeks of storage at 20 °C, a further 2 weeks dry storage at 15 °C before planting resulted in 1 month earlier flowering with no reduction of the number of flowering stems. As dry storage at 20 °C increased to 11 months, the time to emergence and flowering decreased. After dry storage at 20 °C for 12 months, the primary flower stems aborted and secondary stems then developed. Secondary and tertiary flower stems tend to commence flower bud development after the flower bud on the primary flower stem has reached the gynoecium or anther and ovule stage of initiation.

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Hyeon-Hye Kim, Gregory D. Goins, Raymond M. Wheeler and John C. Sager

Plants will be an important component of future long-term space missions. Lighting systems for growing plants will need to be lightweight, reliable, and durable, and light-emitting diodes (LEDs) have these characteristics. Previous studies demonstrated that the combination of red and blue light was an effective light source for several crops. Yet the appearance of plants under red and blue lighting is purplish gray making visual assessment of any problems difficult. The addition of green light would make the plant leave appear green and normal similar to a natural setting under white light and may also offer a psychological benefit to the crew. Green supplemental lighting could also offer benefits, since green light can better penetrate the plant canopy and potentially increase plant growth by increasing photosynthesis from the leaves in the lower canopy. In this study, four light sources were tested: 1) red and blue LEDs (RB), 2) red and blue LEDs with green fluorescent lamps (RGB), 3) green fluorescent lamps (GF), and 4) cool-white fluorescent lamps (CWF), that provided 0%, 24%, 86%, and 51% of the total PPF in the green region of the spectrum, respectively. The addition of 24% green light (500 to 600 nm) to red and blue LEDs (RGB treatment) enhanced plant growth. The RGB treatment plants produced more biomass than the plants grown under the cool-white fluorescent lamps (CWF treatment), a commonly tested light source used as a broad-spectrum control.

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Changhoo Chun, Ayumi Watanabe, Toyoki Kozai, Hyeon-Hye Kim and Junya Fuse

Spinach (Spinacia oleracea L. cv. Dimple) was chosen to determine whether bolting (i.e., elongation of flower stalks) could be controlled by manipulating the photoperiod during transplant production in a closed system using artificial light. Plants grown under various photoperiods during transplant production were transferred and cultured under natural short photoperiods and artificial long photoperiods. Vegetative growth at transplanting tended to be greater with the longer photoperiod because of the increased integrated photosynthetic photon flux. Bolting initiation reacted qualitatively to a long photoperiod, and the critical photoperiod for bolting initiation was longer than 13 h and shorter than 15 h. The plants grown under a longer photoperiod during transplant production had longer flower stalks at harvest. The long photoperiod and/or high temperature after transplanting therefore promoted flower stalk elongation. Growing plants under a photoperiod that was shorter than the critical photoperiod during transplant production reduced elongation of the flower stalks, thus there was no loss of market value even though the plants were cultured under a long photoperiod and high temperature for 2 weeks after transplanting.

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Gioia D. Massa, Hyeon-Hye Kim, Raymond M. Wheeler and Cary A. Mitchell

Light-emitting diodes (LEDs) have tremendous potential as supplemental or sole-source lighting systems for crop production both on and off earth. Their small size, durability, long operating lifetime, wavelength specificity, relatively cool emitting surfaces, and linear photon output with electrical input current make these solid-state light sources ideal for use in plant lighting designs. Because the output waveband of LEDs (single color, nonphosphor-coated) is much narrower than that of traditional sources of electric lighting used for plant growth, one challenge in designing an optimum plant lighting system is to determine wavelengths essential for specific crops. Work at NASA's Kennedy Space Center has focused on the proportion of blue light required for normal plant growth as well as the optimum wavelength of red and the red/far-red ratio. The addition of green wavelengths for improved plant growth as well as for visual monitoring of plant status has been addressed. Like with other light sources, spectral quality of LEDs can have dramatic effects on crop anatomy and morphology as well as nutrient uptake and pathogen development. Work at Purdue University has focused on geometry of light delivery to improve energy use efficiency of a crop lighting system. Additionally, foliar intumescence developing in the absence of ultraviolet light or other less understood stimuli could become a serious limitation for some crops lighted solely by narrow-band LEDs. Ways to prevent this condition are being investigated. Potential LED benefits to the controlled environment agriculture industry are numerous and more work needs to be done to position horticulture at the forefront of this promising technology.