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Jae-Young Lee*, Yong-Koo Kim and Hee-Seung Park

To maintain appropriate tree shapes for Asian pear trees, multi-leader system would be more suitable, which could be obtained from the proper training systems. Controlling apical dominance should be the major factor for tree shape management and this might be modified by branch bending or pruning methods. When the tree shape was managed with Alternate Fan System, too narrower branch angle depressed flower bud formation because of the vigorous shoot growth but too wider angle also decreased that formation because of the numerous water sprouts. The tree with 75 degrees of internally deviated angle performed superior result in fruiting process. Additionally, heading-back pruning could be another for water sprout emerging. For that reason, the severer heading-back pruning stimulated the more water sprout emerging. The proper pruning method could be obtained by considering the relation between main stem width and sum of remained branch width.

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Hyun-Hee Han*, Yong-Koo Kim and Jae-Young Lee

The nitrogen contents of leaves were the same on the first measurement of 9 May 2003 and the date was immediately prior date to application of different training angles to the one-year-old shoots grown during the previous year. However, the nitrogen content began to be different according to training angles as early as 8 days after the training of one-year-old branches. The 90° branch showed higher nitrogen content on the eighth date from the training application against 120° or non-trained slanting branch. The 90° branch continuously demonstrated larger nitrogen contents on 23 May and 2 June against non-trained branch. While, the 120° branch began to show the tendency of larger nitrogen content compared with slanting branches from 23rd May which was 2 weeks from training, and this difference continued up to 2 June 2003. The chlorophyll (SPAD value) of the leaves trained to 120° and 90° were the same at the time of initial training was applied on 9t May 2003, but a significant reduction of the chlorophyll (SPAD value) was found as early as eighth date from the first training date and this difference was reduced to be the same on the date of 2 weeks after the initial training date, but the chlorophyll (SPAD value) became different again on 2 June 2003. Correlations between chlorophyll contents (SPAD value) and photosynthetic rates influenced by training angles were highly positive in 90° training and in 120-degree training than non-training. Additionally, the correlations between the specific leaf weight and chlorophyll contents (SPAD value) were highly positive in 120° training than in 90° training or non-training.

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Sung Kyeom Kim, Duk Jun Yu, Ro Na Bae, Hee Jae Lee and Changhoo Chun

Grafted transplants are widely used for watermelon culture in Korea mainly to reduce the yield and quality losses caused by soil-borne diseases. It is normal practice to cure the grafted transplants under high relative humidity (RH) and low photosynthetic photon flux (PPF) conditions for a few days after grafting to prevent the wilting of the transplants. Transpiration rate (TR) and net photosynthetic rate (NPR), however, could be suppressed under those environmental conditions. In the present study, TR and NPR of the grafted watermelon transplants were compared during graft union formation under 18 environmental conditions combining two air temperatures (20 and 28 °C), three RHs (60%, 80%, and 100%), and three PPF s (0, 100, and 200 μmol·m-2·s-1). Percentages of graft union formation and survival were also evaluated. TR and NPR dramatically decreased just after grafting but slowly recovered 2 to 3 days after grafting at 28 °C. The recovery was clearer at higher PPF and lower RH. On the other hand, the recovery of TR and NPR was not observed in 7 days after grafting at 20 °C. Differences in TR and NPR affected by RH were nonsignificant. Percentage of graft union formation was 98% when air temperature, RH, and PPF were 28 °C, 100%, and 100 μmol·m-2·s-1, respectively, which was the highest among all the treatments. Percentage of survival was over 90% when air temperature was 28 °C and RH was higher than 80% (when vapor pressure deficit was lower than 0.76 kPa). In addition, higher PPF enhanced TR and NPR and promoted rooting and subsequent growth of grafted transplants. Results suggest that the acclimation process for grafted watermelon transplants can be omitted by properly manipulating environmental factors during graft union formation.

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Yong In Kuk, Jae Hong Lee, Han Yong Kim, Soon Ju Chung, Gap Chae Chung, Ja Ock Guh, Hee Jae Lee and Nilda R. Burgos

To determine whether chilling tolerance is related to cold acclimation, changes in physiological responses and activity of antioxidative enzymes were investigated in leaves of cucumber (Cucumis sativus L.) grown in controlled environments. Plants were exposed to 15 °C (cold-acclimated) or 25 °C (nonacclimated) for 3 days, under 50 μmol·m-2·s-1 photosynthetic photon flux and 70% relative humidity. Plants were then exposed to 8 °C chilling temperature for 3 days, and allowed to recover in a growth chamber at 25 °C for 3 days. Measurements of leaf water content, cellular leakage, lipid peroxidation, chlorophyll a fluorescence, and quantum yield showed that cold-acclimated leaves were less affected by chilling compared to nonacclimated leaves. Cold-acclimated leaves recovered faster than nonacclimated leaves with regard to all variables examined. Catalase and ascorbate peroxidase activities were induced in cold-acclimated leaves, but not in nonacclimated leaves. These data indicate that cold acclimation increased chilling tolerance of cucumber in association with antioxidative enzymes.

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Kang Hee Cho, Seo Jun Park, Su Jin Kim, Se Hee Kim, Han Chan Lee, Mi Young Kim and Jae An Chun

Blueberry cultivars have traditionally been identified based on the evaluation of sets of morphological characters; however, distinguishing closely related cultivars remains difficult. In the present study, we developed DNA markers for the genetic fingerprinting of 45 blueberry cultivars, including 31 cultivars introduced from the United States Department of Agriculture. We obtained 210 random amplified of polymorphic DNA (RAPD) markers using 43 different primers. The number of polymorphic bands ranged from three (OPG-10 and OPQ-04) to eight (OPR-16), with an average of five. A cluster analysis performed with the unweighted pair group method using arithmetic averages produced genetic similarity values among the blueberry cultivars ranging from 0.53 to 0.85, with an average similarity of 0.68. A dendrogram clustered the 45 blueberry cultivars into two main clusters, with a similarity value of 0.65. Cluster I consisted of four rabbiteye cultivars (Pink Lemonade, Alapaha, Titan, and Vernon) and the Ashworth northern highbush cultivar. Cluster II consisted of 31 northern highbush cultivars, eight southern highbush blueberry cultivars, and Northland half-highbush blueberry cultivar. Fifty five RAPD fragments selected were sequenced to develop sequence-characterized amplified region (SCAR) markers, resulting in the successful conversion of 16 of 55 fragments into SCAR markers. An amplified polymorphic band has the same size as the RAPD fragment or smaller according to the primer combinations in the 16 SCAR markers. Among these markers, a combination of 11 SCAR markers provided sufficient polymorphisms to distinguish the blueberry cultivars investigated in this study. These newly developed markers could be a fast and reliable tool to identify blueberry cultivars.