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Young-Seok Kwon and Fenny Dane

Watermelon (Citrullus lanatus Thumb. Matsum. and Nakai) flower petals usually are yellow, but in watermelon line Kw-695, light-green flowers were detected. To study the inheritance of light-green flower color, Kw-695 plants were crossed with yellow-flowered Korean cultures `SS-4' and `Dalgona'. The resulting F1, F2, and reciprocal backcross generations were analyzed for flower color. Segregation ratios in the F2 and backcross to Kw-695 were 3 yellow: 1 light green and 1 yellow: 1 light green, respectively. Backcross generations to the yellow-flowered parents showed yellow flowers only. These results indicate that inheritance of the light-green flower character in Kw-695 is governed by a single recessive gene. We propose the gf gene symbol for the green flower trait. Kw-695 plants have large vines with large, light-green leaves. The plants are andromonoecious, have large, oval, bright yellow-green fruit with irregular dark-green stripes, bright yellow-orange, inedible flesh with very low sugar content (about 3.2 °Brix), and light-yellow seeds. The trait should be useful as a marker in watermelon breeding programs. Linkages between this trait and other genetic markers in watermelon will be investigated.

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Jongtae Lee, Byeonggyu Min, Heedae Kim, Juyeon Kim, Young-Seok Kwon and George E. Boyhan

This study evaluated the effects of a nonwoven polypropylene (NPP) covering during overwintering with different mulch types and transplant times on bulb onion growth and yield of intermediate-day onions (Allium cepa L.) during the 2015/2016 and 2016/2017 growing seasons. Field experiments were conducted using a split-split plot design with three replicates. Treatments included main plots containing different mulch types (transparent plastic mulch, black plastic mulch, or bare ground), subplots with different transplanting times (20 Oct., 5 Nov., and 20 Nov.), and sub-subplots containing two onion cultivars (Sunpower and Katamaru). NPP was used to cover all plots on 1 Dec., and it was removed on 28 Feb. Mean daily air temperatures during transplanting and root establishment were 2.6 °C higher during the 2015/2016 growing season compared with the 2016/2017 season. NPP covering on bare ground increased soil temperature by 2.1 °C compared with no treatment. Soil water potential with transparent and black mulches and NPP continued to be more than −10 kPa until early March. Number of leaves, and root and leaf weight were significantly greater during the 2015/2016 growing season than during the 2016/2017 growing season; there were also significantly greater for onion plants grown with transparent plastic mulch than for those grown with black plastic mulch or no mulch on 4 Apr. and 5 May. Marketable bulb yield was lower during 2015/2016 (32.0 Mg·ha−1) than during 2016/2017 (38.5 Mg·ha−1); this was due to the increased unmarketable bulb yield, with 33.2 Mg·ha−1 bolters and 3.9 Mg·ha−1 doubled bulbs during 2015/2016 compared with 3.9 Mg·ha−1 bolters and 0.3 Mg·ha−1 doubled bulbs during 2016/2017. Marketable bulb yield of ‘Katamaru’ (38.9 Mg·ha−1) was greater than that of ‘Sunpower’ (31.6 Mg·ha−1). Marketable bulb yield increased with later transplanting times, and onions grown with black plastic mulch achieved the highest bulb yield (43.0 Mg·ha−1), followed by transparent mulch (34.7 Mg·ha−1) and no mulch (28.0 Mg·ha−1). When the temperatures from early November to early December were similar to the 30-year average temperatures, marketable bulb yield could increase with the NPP covering, especially for onions grown with black plastic mulch or no mulch when transplanted from late October to early November.

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Young-Seok Kwon, Kwang-Soo Cho, Ju-Seong Im, Eung-Ho Lee and Won-Bae Kim

Onions are a major vegetables in Korea. Short-day onions are grown in more than 95% in southern area of South Korea, and long-day onions are grown above 600-m altitude in the highlands. Onion cultivation in the highland areas has become difficult for farmers to obtain high income but stable production because of higher cost of seed and the intensive labor involved in production. Consequently, onion set culture by inexpensive onion seeds compared with expensive F1 seed has an advantage due to the higher proportion of marketable size bulbs. This study was conducted to find out the suitable sowing time and tray size for onion set culture in the highlands—the earlier the sowing time, the higher the number of onions set. The most appropriate sowing date and 1.6–3.5 g of onion set size was early to middle May, also with the highest distribution percentage. The highest set number (780.8 set/m2) of suitable onion set size (1.6–3.5 g) were harvested from the 288 trays, followed by 770 set from the bed (9 g/m2 of seed sowed), and (7/m2 of seed sowed) in the 406 tray.

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Ji Hae Jun, Eun Young Nam, Kyeong Ho Chung, Seok Kyu Yun, Jung Hyun Kwon, Ik Koo Yun, Yong Bum Kwack, Sung Jong Kim and Kang Hee Cho

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Ji Hae Jun, Jung Hyun Kwon, Eun Young Nam, Kyeong Ho Chung, Ik Koo Yun, Seok Kyu Yun, Yong Bum Kwack, Sung Jong Kim and Sang Jo Kang

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Ji Hae Jun, Jung Hyun Kwon, Eun Young Nam, Kyeong Ho Chung, Ik Koo Yun, Seok Kyu Yun, Yong Bum Kwack, Sung Jong Kim and Sang Jo Kang

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Eun Young Nam, Jung Hyun Kwon, Ji Hae Jun, Kyeong Ho Chung, Seok Kyu Yun, Sung Jong Kim and Yun Su Do

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Jung Hyun Kwon, Ji Hae Jun, Eun Young Nam, Kyeong Ho Chung, Ik Koo Yoon, Seok Kyu Yun and Sung Jong Kim

Being self-incompatible, most Asian plums should be planted with a compatible pollinizer to produce fruits. Therefore, the selection of an adequate pollinizer is essential when new plum cultivars are released. To select a suitable pollinizer for ‘Summer Fantasia’ plum, the S genotype, cross-compatibility, pollen viability, and flowering time of five candidate cultivars were evaluated. Using polymerase chain reaction (PCR) analysis, the S genotype of ‘Summer Fantasia’ was determined as S a S c, which was expected to be compatible with other S genotypes. To test cross-compatibility, the trees were covered with caging net to prevent unintended pollination, and pistils were hand pollinated without emasculation. Fruit set percentage was calculated 10 weeks after pollination. The fruit set percentage resulting from the cross between ‘Summer Fantasia’ and ‘Taiyo’ (S b S c) was 13.8%, whereas that resulting from other combinations was less than 5.0%. Pollen germination percentage was investigated to monitor pollen viability; it varied yearly among cultivars, although ‘Formosa’ (10.6%) and ‘Taiyo’ (13.8%) showed the highest pollen germination percentages among the cultivars. When averaged over three years and two locations, ‘Summer Fantasia’ bloomed 2–3 days after ‘Akihime’, ‘Formosa’, ‘Oishiwase’, and ‘Purple Queen’. Blooming period of ‘Summer Fantasia’ and ‘Taiyo’ overlapped almost entirely. Overall, the results indicated that ‘Taiyo’ was the most suitable pollinizer for ‘Summer Fantasia’.

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Eun Young Nam, Ji Hae Jun, Kyeong Ho Chung, Jung Hyun Kwon, Seok Kyu Yun, Ik Koo Yun and Kang Hee Cho