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Ruey-Chi Jao and Wei Fang

Effects of intermittent light on photomixotrophic growth of potato plantlets in vitro and the electrical savings that could be realized by adjusting the frequency and duty ratio of light-emitting diodes (LEDs) were investigated and compared to the use of conventional tubular fluorescent lamps (TFLs). TFLs provide continuous fluctuating light at 60 Hz and LEDs provide continuous nonfluctuating or intermittent/pulse light depend on the preset frequency and duty ratio. In total, eight treatments were investigated with varying light source, frequency, duty ratio and photoperiod. Results indicated that if growth rate is the only concern, LEDs at 720 Hz [1.4 milliseconds (ms)] and 50% duty ratio with 16-h light/8-h dark photoperiod stimulated plant growth the most. However, if energy consumption is the major concern, using LEDs at 180 Hz (5.5 ms) and 50% duty ratio with 16-h light/8-h dark photoperiod would be the best choice for illuminating potato plantlets without significantly sacrificing plant growth, especially when energy for heat removal is also considered.

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Ruey-Chi Jao and Wei Fang

Effects of concurrent vs. alternating blue and red light using light-emitting diodes (LEDs) on the photomixotrophic growth of potato plantlets in vitro were investigated. All seven treatments had the same 5.53 mol·m-2 daily light integral (DLI), photoperiod (16-hour day/8-hour night) and similar proportion of red light (45%) and blue light (55%). Results showed that the fresh/dry weight accumulation of potato plantlets in vitro under the concurrent blue and red light was superior than that under the alternating blue and red light, indicating that the simultaneous coexistence of blue and red light are necessary for optimum plantlet growth. Low PPF with long duration was better than high PPF with short duration under same DLI. Within the concurrent blue and red light treatments, when the duration of blue light was shorter than that of red light, timing of the blue light affected the growth of potato plantlets in vitro. Providing blue and red light together at the beginning of the photoperiod resulted in optimal growth, however plantlets illuminated with alternately blue and red light had significantly less fresh/dry weight accumulation.

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Ruey-Chi Jao, Chien-Chou Lai, Wei Fang and Sen-Fuh Chang

Effects of light generated by red and blue light-emitting diodes on the photomixotrophic growth of Zantedeschia jucunda `Black Magic' plantlets in vitro and tuber formation after transplant under the same PPF and photoperiod were investigated. All five treatments had the same photosynthetic photon flux (PPF, 80 ± 5 μmol·m-2·s-1) and photoperiod (16 hours daytime/8 hours nighttime), leading to the same daily light integral. Results showed that the tubular fluorescent lamp (TFL) treatment had the highest value on chlorophyll content and dry weight accumulation than other treatments using light-emitting diodes (LEDs). In LED treatments, there were no significant differences on dry weight and growth rate but with significant differences on chlorophyll content and plant height when blue light LEDs were added. It revealed that blue light was involved in plant height and chlorophyll development control mechanism. Results also showed that minor difference in 28 days of transplant production (in vitro) among treatments does not extends after 6 months of tuber formation stage grown in greenhouse. At present, blue LEDs cost much more than that of red LEDs, results of this study suggested that using red LEDs alone and powered with AC is feasible for the commercial production of Zantedeschia plantlets in vitro.