1Department of Environmental Horticulture, The University of Seoul, Jeonnong-dong 90, Dongdaemun-gu, Seoul 130-734, South Korea.
2Advance Radiation Technology Institute, KAERI, Jeongeup, Jeonbuk 580-185, South Korea.
3National Institute of Crop Science, RDA, Muan, Jeonnam 293-5, South Korea.
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