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  • Author or Editor: Jung-Myung Lee x
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A non-destructive screening system for resistance to multiple diseases was devised by utilization of excised plant parts such as leaf, shoot and fruit, which would allow evaluation of the same tested plants for reaction to major diseases and for other horticultural traits as well. A simple device made it possible to maintain freshness of the excised leaves and shoots long enough for the symptoms to develop fully. By inoculating suspension of bacterial leaf spot disease to the leaves excised, three genetic reactions, i.e, vertical resistance, horizontal resistance and susceptibility, were discerned as successfully as when inoculated on the intact leaves. `CM331' and `PI201234', of which resistance to Phytophthora blight had been shown in conventional screening by drenching at the seedling stage, also revealed the resistance when the inoculation was directly given to the excised shoot. Inoculation of anthracnose by high pressure spray resulted in more distinct differences between genotypes and less variation within genotypes than the conventional method by pins. Local lesions were observed in 6 days after inoculation of TMV on both excised and those kept intact on the plant in the resistant varieties. It was confirmed that excision of the plant parts for the disease screening by the new method gives little influence on the growth and yield of the plants being tested.

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Use of grafted seedlings is a practical method to overcome salt accumulation, deterioration of physicochemical properties of soil, and accumulation of soil-borne pathogen that farmers, as well as commercial plug seedling producers, in Korea mainly adapted. Graft-take, subsequent growth, and quality characteristics of grafted hot pepper (Capsicum annuum L.) seedlings composed of three scions and 10 rootstocks were investigated. `Manita', `Chungyang', and `Nokkwang' were cultivars of scions used—they are the major hot pepper cultivars in Korea. The ten rootstock cultivars can be categorized into three groups: cultivars specially bred for rootstocks (`Konesian Hot', `PR-380', `R-Safe', and `Tantan'); cultivars recently bred in NHRI, Korea with the potential to be rootstocks (`Wonkwang1' and `Wonkwang2'); and cultivars originally bred for fruit harvest, but used as rootstocks due to their tolerance to soil-borne pathogens (`Kataguruma', `PR-Data', `PR-Gangza', and `PR-Power'). All the plants were treated with 5 mg·L-1 diniconazole solution 2 weeks after grafting and were soaked into 1.4% salt solution for 48 hours about 5 weeks after grafting. All the grafted seedlings showed feasible growth, including normal flowering and fruit set, and any symptoms of phytophthora blight and anthracnose were not found during 17-day-long experiment. Seedlings grafted onto `Tantan' rootstock showed stronger tolerance to high salt concentration than those grafted onto other rootstocks. Use of some, such as `Wongang 1', `PR-Data' and `Kataguruma', was alleviated the salt-induced growth inhibition.

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Dry heat treatment has been commonly used to inactivate some seed-borne pathogens in vegetable seeds. Virtually all the gourd seeds for watermelon rootstock are being treated with dry heat to inactivate cucumber green mottle mosaic virus (CGMMV, a strain of tobamovirus) and Fusarium. Seeds of five gourd and one squash cultivars were treated with dry heat (35 °C for 24 h + 50 °C for 24 h + 75 °C for 72 h) and, immediately after the dry heat treatment, the seeds (moisture content of 1% or lower) were allowed to absorb atmospheric moisture in a moisture saturated chamber until the seed moisture contents reached 2% to 8%. After the equilibrium obtained, the seeds were sealed in air-tight bags and stored for 1 day or 30 days at 20 °C. The seeds were then sown in cell trays and the emergence and seedling characteristics were evaluated. Dry heat treatment caused significant delay in emergence in all tested cultivars, but had little or no influence on the final emergence rate. Moderate to severe injury was observed in seedlings grown from dry heat-treated seeds in three out of six cultivars tested. However, little or no dry heat phytotoxicity was observed in other cultivars, thus suggesting the marked differences in cultivar susceptibility to dry heat treatment. Rapid humidification before sealing also appeared to reduce the early emergence rate in some cultivars, but had no effect on the final emergence rate in most cultivars. Storage of dry heat-treated seeds in sealed bags for 30 days before sowing was highly effective in minimizing the phytotoxicity symptoms in seedlings as compared to the seedlings grown from the seeds sown immediately after the dry heat treatment. This suggests that the reestablishment of metabolic process required for normal seed germination requires a long period after the dry heat treatment. Other characteristics associated with DH treatment will also be presented.

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Grafting is common in all cucurbits in Asia, and gourd (Lagenaria siceraria) is the most popular rootstock for watermelons. Since the grafting is practiced at very early stage (right after the cotyledon expansion), uniform germination of rootstocks as well as the scions is crucial for grafting efficiency. Seeds were divided into three groups; intact, dry-heat treated (75 °C for 72 h), and brushed (575 rpm for 5 min). In each group, various solid matrix priming (SMP) treatments were imposed. Microcel E was used for SMP treatment with water or chemical solutions (10 seed: 1 Microcel E: 3 water, by weight). SMP treatment promoted earlier seed germination in all tested cultivars, thus resulting in higher rate of graftable seedlings. Brushing before SMP further enhanced earlier and uniform seed germination. Dry heat treatment, which can eliminated the seed-borne Fusarium spp. and virus, significantly delayed the early germination although the final germination percentage was not influenced. The characteristics of seedlings will also be presented.

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The effectiveness of solid matrix priming (SMP) and seed brushing was further evaluated by using an thermo-gradient table (Seed Processing, Holland) set at 10 different temperatures from 12 to 30 °C. Intact or brushed seeds of gourd (Lagenaria siceraria) were primed with Micorocel E (Celite Corp.) at 25 °C for 3 days in the mixture of 10 seed: 1 Microcel E: 3 water, by weight, and the primed seeds were dried again for long-term storage. SMP treatment significantly increased earlier seed germination at all temperatures. However, the difference in seed germination rate between intact and SMP-treated seeds was most pronounced at somewhat lower temperatures of 18-22 °C. SMP-treated seed showed about 20% final germination rate at 12 °C, whereas intact seeds did not germinate at all. Seed brushing treatment itself did not influenced the germination rate. However, brushing treatment before SMP treatment significantly increased the SMP effect. Combined use of chemicals in solution further increased the early germination. Details of various seed treatment methods will be presented.

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Soybean sprouts are one of the most-favored traditional vegetables around the world. The sprouts are usually consumed 7 to 10 days after sowing depending upon the growing conditions. High-quality sprouts should have less secondary roots, short and well-swollen hypocotyls in pure white color, and small cotyledons in hooked position. Cytokinins were reported to be effective in producing such sprouts by promoting sprout growth while inhibiting the excessive hypocotyl elongation and secondary root growth. Seeds of four soybean cultivars with different characteristics were soaked in water for 4 h and, 2 to 3 h after the imbibition, the seeds were soaked again in solutions of different cytokinins such as benzyladenine (BA), BA-riboside (BAR), BPA, 2iP, 2iP-riboside, 4-CPPU, and kinetin-riboside (KR) for 10 min. After the treatment, the sprouts were grown in a plastic tube (25 cm height × 10.5 cm diameter) a dark culture room with ample watering every 4 h. After 7 days of growth, uniform samples were taken from each treatment and the sprout characteristics were examined. Some cytokinins such as BA, BAR, 4-CPPU were highly effective in promoting the sprout growth (fresh weight) even though the hypocotyl length was markedly reduced. Other cytokinins such as 2iP, 2iPR, and KR had no effect on sprout growth. Hypocotyl diameter was markedly increased by BA and 4-CPPU treatment, thus resulting in short, strong and good quality sprouts. Cultivars responded differently to cytokinin treatment by showing different growth promotion depending upon the sprout parts. Injury-like symptoms, abnormal and twisted heads or cotyledons, appeared in cytokinin-treated sprouts at high concentrations and the symptoms were severe when the sprouts were grown at high temperatures. In all the cultivars tested, BAR appeared to be better than others in terms of sprout quality and growth promoting characteristics.

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Washing oriental melon (Cucumismelo var. makuwa Makino) is a standard procedure because it facilitates the precise elimination of defective fruit, such as fruit having internal decay symptoms, and also facilitates easier handling of fruit by the elimination of gummy substances on the fruit surface. In most fresh fruits and vegetables, however, washing has never been recommended unless it is related to other practices, such as waxing or immediate processing. Harvested oriental melons were placed in a big water tank and washed with a brush machine immediately before grading, using an automatic grader. Fruit that had sunk down to the bottom of the tank were discarded, as they were premature-fermented fruit with no commercial value. Fruit, intact or washed, were treated with 1-MCP at 0.5–2.0 ppm for 12 hours and stored at room temperature for 3 weeks. Flesh firmness, soluble solids contents, fruit petiole color, and changes of surface suture color were measured to evaluate storability of the fruit. The washed fruit exhibited poor skin color and early suture-browning as compared to the non-washed fruit, regardless of 1-MCP pretreatment. 1-MCP treatment was also effective in maintaining fresh fruit quality as compared to the non-treated fruit. 1-MCP effects were, however, more pronounced in relatively smaller and less mature fruit as compared to the fully mature fruit. 1-MCP was also effective in maintaining white suture color, the most important visual factor currently used for quality evaluation in oriental melon.

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Double-stemmed seedlings (DSS) will be favored by the growers because they can save the expense needed to purchase commercial seedlings. This is also true with grafted tomatoes since the price of grafted tomato seedlings is about 2 times higher than non-grafted ones. The plug seedling growers will also benefit from the increased demand for DSS if the production cost for DSS can be maintained at appropriate level. Two stem cuttings having two expanded leaves were taken from a seedling when the seedling had four expanded leaves and rooted in 32-cell trays filled with commercial soil mix. Lower stem cuttings having first and second leaves produced well-balanced DSS even without any plant bioregulator treatment whereas up upper stem cuttings having third and fourth leaves resulted in single-stem seedlings with very limited outgrowth of axillary shoot from the third node. DSS can be obtained from the decapitated seedling stump by outgrowth of axillary shoots from the cotyledonary nodes, but the quality and uniformity were inferior to other seedlings. Pinching off the tips of seedlings thus leaving three expanded leaves per seedling and application of plant bioregulators to the decapitated seedlings were also effective for producing DDS. Application of thidiazuron (TDZ) in lanolin paste to the second node was most effective even though whole plant spray with TDZ or BA was also partially effective. Subsequent growth characteristics of these seedlings will be further discussed.

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A series of experiments were conducted to investigate the effects of chlorocholine and similar compounds such as choline, chlorocholine chloride (CCC or chlormequat) and other compounds on the rooting and seedling quality for transplanting. The growth of shoot and root and the ratio of shoot/root were influenced and consequently the seedling quality was improved by chlorocholine treatment. Mungbean bioassays for plant hormone revealed that rooting was promoted and shoot growth or stem elongation was inhibited by the treatment. Addition of other PGRs such as atonik, vitamins and surfactants to chlorocholine solution significantly promoted the rooting of mungbean cuttings as well as the rooting of cutting of sweet potato, cucumber, and watermelon.

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Growth response of `Sambok Honey' watermelon grafted onto different rootstocks, including four Citrullus rootstocks and three other cucurbitaceous rootstocks, was evaluated at low and normal temperature regimes. Marked reduction in plant growth rate was observed in plants grown at low temperatures as compared to those grown at normal or optimal temperatures. Relative growth reduction rates were 40% to 48% for vine length, 39% to 51% for total leaf area, 37% to 60% for shoot fresh weight, and 50% to 79% for shoot dry weight, respectively. Watermelon rootstock PI 482322 showed comparable plant growth as the most popular rootstock (Shintozwa pumpkin) even at low temperatures. `Sambok Honey' watermelon grafted onto watermelon hybrids `PI 271969 × PI 296341' and `PI 271769 × Calhoun Gray', showed comparable plant growth as FR Dantos bottle gourd rootstock. Index of growth ability at low temperature (IGALT), which was calculated on the basis of reduced rate of vine length, dry weight, and leaf area, was comparatively high in C. martinezii, Shintozwa, PI 482322, and `PI 271769 × PI 296341' rootstocks (50% or higher) and lowest in own-rooted `Sambok Honey' or in watermelon plants on `Knight' rootstock. Watermelon hybrids `PI 271969 × PI 296341' and `PI 271769 × Calhoun Gray' exhibited better or at least comparable growth at low temperatures as compared to `FR Dantos', thus confirming the feasibility of using watermelon rootstocks even in winter greenhouse conditions.

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