• Journal of the Earthquake Engineering Society of Korea
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• v.10 no.3 s.49
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• pp.125-134
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• 2006

Conventional methods for the assessment of liquefaction potential were primary for severe earthquake regions $(M{\geq}7.5)$ such as North America and Japan. In Korea, an earthquake related research has started in 1997, but most contents in the guidelines were still quoted from literature reviews of North America and Japan, which are located in strong earthquake region. Those are not proper in a moderate earthquake regions including Korea. Also the equivalent uniform stress concept (Seed & Idriss, 1971) using regular sinusoidal loading which is used, in a conventional method for the assessment of liquefaction potential, can't reflect correctly the dynamic characteristics of real irregular earthquake motions. In this study, cyclic triaxial tests using irregular earthquake motions are performed with different earthquake magnitudes, relative densities, and fines contents. Assessment of liquefaction potential in moderate earthquake regions is discussed based on various laboratory test results. From the results, screening limits in seismic design were re-investigated and proposed using normalized maximum stress ratios under real irregular earthquake motions. Also from the tests using constant wedge loading and incremental wedge loading, the characteristics of liquefaction resistance of saturated sand under irregular ground motions are investigated.

• KSBB Journal
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• v.20 no.5 s.94
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• pp.376-382
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• 2005

Avermectin (AVM) $B_{1a}$ produced by Streptomyces avermitilis via polyketide pathway is a secondary metabolite with powerful anthelmintic and insecticidal activities, thus being used as an efficient agent in the field of agriculture and animal health. It has been reported that a precursor for AVM $B_{1a}$ biosynthesis was isoleucine and the biosynthetic pathway of AVM $B_{1a}$ was closely similar to that of fatty acid. Based on understanding of the biosynthetic pathway of AVM $B_{1a}$, we intended to screen various mutants resistant against O-methyl threonine (OMT), an isoleucine-anti metabolite, and/or mutants resistant against p-fluoro phenoxy acetic acid (pFAC), an inhibitor of fatty acid biosynthesis. It was inferred that these mutants could produce AVM $B_{1a}$ more efficiently, due to the acquired capability of not only overproducing isoleucine intracellularly but also channelling metabolized carbon-sources into the polyketide pathway, thus leading to enhanced biosynthesis of AVM $B_{1a}$. The resulting mutant (PFA-1 strain) resistant against 100 ppm of pFAC was able to produce approximately 42 fold higher amount of AVM $B_{1a}$ compared to the parallel mother strain (4,200 vs. 100 units/l). In addition, through the process of continuous strain improvement program carried out by gradually increasing the OMT concentration, it was possible to obtain a more attractive mutant with greater AVM $B_{1a}$ production capacity (9,000 units/l). Notable was that significantly higher producer (12,000 units/l) could be selected through further screening of the resistant mutants, this time, to even higher concentration of PFAC. Meanwhile, through the analysis of AVM Bla production histograms (i.e., number of strains according to their AVM $B_{1a}$ biosynthetic ability) for the earlier strains in comparison with the high producers having the characteristics of resistance to OMT and pFAC, it was found that production stability of the high-yielding producers were remarkably improved, as demonstrated by the fact that larger proportion of the mutated strains had greater capability of AVM $B_{1a}$ biosynthesis ($71\%$ in the range between 5,000 and 7,000 units/L; $47\%$ in the range between 6,000 and 7,000 units/l). Based on these consequences, it was concluded that the rational screening strategy based on the understanding of the biosynthetic pathway of AVM $B_{1a}$ was very effective in obtaining high-yielding mutants with the features of enhanced production stability.

• Korean Journal of Organic Agriculture
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• v.24 no.4
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• pp.945-955
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• 2016

To date, chemical managements of plant bacterial diseases are complicated by limitations on use of antibiotics in agriculture, antibiotic resistance development, and limited efficacy of alternative control agents. In this study, thus, we performed screening of eco-friendly farming material (notice no. 2-4-064) containing tannic acid as new antibacterial-activity against 7 plant bacterial pathogens: Pectobacterium carotovorum subsp. carotovorum (Pcc), Ralstonia solanacearum (Rs), Acidovorax avenae subsp. citrulli (Aac), Xanthomonas cirti pv. citri (Xcc), Erwinia pyrifoliae (Ep), Clavibacter michiganensis subsp. michiganensis (Cmm), and Streptomyces scabies (Sc), Initial screening of antibacterial effects of eco-friendly farming material was performed using the paper disk diffusion method and co-cultivation in broth culture. Tannic acid based eco-friendly farming material showed inhibitory effect against Pcc, Rs, Aac, Xcc, Cmm, and Ss, whereas it did not show inhibition zone against Ep. However, when it tested by co-cultivation in broth culture, it showed strong inhibition effect against all pathogens that declined growth curve compared to bacterial pathogen only. Interestingly, when we observed morphological changes on those pathogens by SEM, cell morphologies of 7 pathogens were slightly changed that seem to be malfunction in their cell envelope.

• Journal of Microbiology and Biotechnology
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• v.12 no.1
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• pp.121-129
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• 2002

Using recombinant Chinese hamster ovary (CHO) cells, strategies for developing high producers for the recombinant human Transforming Growth $Factor-{\beta}1$ ($TGF-{\beta}1$) protein are proposed and their physiological characteristics in cell cultures were investigated. $TGF-{\beta}1$ is a pleiotrophic polypeptide involved in various biological activities, including cell growth, differentiation, and deposition of extracellular matrix proteins. The CHO cells included human $TGF-{\beta}1$ cDNA in conjunction with a dihydrofolate reductase (DHFR) gene, which was cotransfected into the cells to amplify the transfected $TGF-{\beta}1$ cDNA. As a first-round screening of the transfected cells, a relatively high $TGF-{\beta}1$-producing cell line was selected, and then, it acquired a resistance to increasing concentrations of methotrexate (MTX) up to $60{\mu}M$,resulting in a significant improvement in its $TGF-{\beta}1$ biosynthetic ability. After applying a monoclonal selection strategy to the MTX-resistant cells, more productive cells were screened, including the APP-3, App-5, and App-8 cell lines. These high producers were compared with two other cell lines (AP-l cell line without amplification of transfected $TGF-{\beta}1$ cDNA and nontransfectant of $TGF-{\beta}1$ cDNA) in terms of cell growth, $TGF-{\beta}1$ productivity, sugar uptake, and byproduct formation, in the presence or absence of MTX in the culture medium. Consequently, both monoclonal selection as well as an investigation of the physiological characteristics were found to be needed for the efficient screening of higher $TGF-{\beta}1$ producers, even after the transfection and amplification of the transfected gene.

• Microbiology and Biotechnology Letters
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• v.35 no.4
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• pp.278-284
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• 2007

A novel screening strategy for salt-resistant antimicrobial peptides from a M13 peptide library was developed. Fusion of MSI-344, a magainin derivative and indolicidin to pIII coat proteins did not significantly affect viability of the recombinant phages, which indicated that the pIII could neutralize toxicity of the antimicrobial peptides and therefore it is possible to construct antimicrobial peptide library in Escherichia coli. On the basis of the conserved sequence of ${\alpha}$-helical antimicrobial peptides, a semi-combinatorial peptide library was constructed in which the peptides were displayed by pIII. To remove hemolytic activity from the library, the phages bound to red blood cells were removed, and the subtracted phage library was screened for binding to target bacteria Pseudomonas aeruginosa and Staphylococcus aureus under high salt concentrations. The screened peptides showed relatively low antimicrobial activity against the target bacteria. However, antimicrobial activities of the screened peptides P06 and S18 were not affected by the cation concentrations of 150 mM $Na^+$, 2 mM $Mg^{2+}$ and 2 mM $Ca^{2+}$ without significant hemolytic activity. This screening strategy that is based on binding capacity to target cells provides new potential to develop salt-tolerant antimicrobial peptides.

• Horticultural Science & Technology
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• v.32 no.1
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• pp.66-76
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• 2014

Resistance of one hundred commercialized cultivars of chili pepper to four isolates of Phytophthora capsici was evaluated under controlled environmental conditions. The cultivars are commercialized as resistant (59%) and susceptible (41%) to Phytophthora blight in Korea. Mean disease severities of the cultivars on P. capsici MY-1, KPC-1, JHAI1-7, and KPC-7 isolates were 37, 55, 60, and 74%, respectively. In addition, 38 for MY-1, 48 for KPC-1, 56 for JHAI1-7, and 76 cultivars for KPC-7 showed susceptibility. To P. capsici MY-1, the weakest pathogenicity isolate among them, 59 cultivars represented high resistance. By contrast, only six cultivars showed high resistance to P. capsici KPC-7, the strongest isolate. Furthermore, resistance of most cultivars except for three cultivars was negatively correlated with the virulence of P. capsici isolates. And isolate-specific resistance of the chili pepper cultivars could not be found. Among them, six cultivars showing resistance to all the tested isolates were selected for further study. The development of Phytophthora blight on the six cultivars according to inoculum density ($5{\times}10^4$ to $1.5{\times}10^6$ sporangia/pot) and incubation temperature (25 to $30^{\circ}C$) after inoculation of P. capsici was tested. Resistance of the cultivars to P. capsici KPC-1 and JHAI1-7, moderately pathogenic isolates, was hardly affected. But to KPC-7 isolate, the highly resistant cultivars showed susceptiblility or moderate resistance when the seedlings were inoculated with inoculum density of $1.5{\times}10^6$ sporangia/pot and incubated at 28 to $30^{\circ}C$. From these results, it is likely that resistance of chili pepper cultivars to Phytophthora blight is affected by the virulence of P. capsici isolate.

• Applied Biological Chemistry
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• v.48 no.4
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• pp.339-344
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• 2005

Rice blast, which is caused by the fungus Magnaporthe grisea, is one of the most destructive diseases of rice. To identify genes involving in the signal transduction pathways that mediate rice blast resistance, we screened over 2,000 mutant lines of a highly resistant variety RIL260 that were generated by using a DEB (1, 3-Butadiene diepoxide) treatment method. In the mutant population, the frequency of albino plants was 6.7%, indicating that this population has a high frequency of mutations in the genome. The primary screening identified 29 mutant plants that exhibit a complete or partial loss of the resistance to rice blast. Among them, M5465, the most susceptible line, was subsequently examined by DNA gel-blot experiments using DNA molecular markers of Pi5(t) that has been previously identified as a durable resistance locus in RIL260. The result revealed that a large deletion and rearrangement of genomic DNA occurred in the Pi5(t) locus. The results suggest that DEB can be used as an efficient mutagen to induce large scale mutations in the rice genome. The isolated mutants should be useful for elucidating the Pi5(t)-mediated signaling pathways of rice blast resistance.

• Proceedings of the Korean Society of Crop Science Conference
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• 2017.06a
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• pp.92-92
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• 2017

Bakanae disease is one of the most serious and oldest problems of rice production, which was first described in 1828 in Japan. This disease has also been identified in Asia, Africa, North America, and Italy. Germinating rice seeds in seed boxes for mechanical transplantation has caused many problems associated with diseases, including bakanae disease. Bakanae disease has become a serious problem in the breeding of hybrid rice, which involves the increased use of raising plants in seed beds. The indica rice variety Shingwang was selected as resistant donor to bakanae disease. One hundred sixty nine NILs, YR28297 ($BC_6F_4$) generated by five backcrosses of Shingwang with the genetic background of susceptible japonica variety, Ilpum were used for QTL analysis. Rice bakanae disease pathogen, CF283, was mainly used in this study and inoculation and evaluation of bakanae disease was performed with the method of the large-scale screening method developed by Kim et al. (2014). SSR markers evenly distributed in the entire rice chromosomes were selected from the Gramene database (http://www.gramene.org), and the polymorphic markers were used for frame mapping of a $BC_5F_5$ resistant line. Here, we developed 168 near-isogenic rice lines (NILs, $BC_6F_4$) to locate a QTL for resistance against bakanae disease. The lines were derived from a cross between Shingwang, a highly resistant variety (indica), and Ilpum, a highly susceptible variety (japonica). The 24 markers representing the Shingwang allele in a bakanae disease-resistant NIL, YR24982-9-1 (parental line of the $BC_6F_4$ NILs), were located on chromosome 1, 2, 7, 8, 10, 11, and 12. Single marker analysis using an SSR marker, RM9, showed that a major QTL was located on chromosome 1. The QTL explained 65 % of the total phenotype variation in $BC_6F_4$ NILs. The major QTL designated qBK1 was mapped in 91 kb region between InDel15 and InDel21. The identification of qBK1 and the closely linked SSR marker, InDel18, could be useful for improving rice bakanae disease resistance in marker-assisted breeding.

• Horticultural Science & Technology
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• v.30 no.2
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• pp.171-177
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• 2012

A total of 94 tomato accessions were evaluated for the resistance to $Tomato$ $spotted$ $wilt$ $virus$ (TSWV) using a Sw5-2 SCAR marker and bioassay. PCR products of the marker were approximately 574 bp, 500 bp, and 462 bp, among which the longest was linked to TSWV resistance allele of Sw5-b. This allele was only found in three accessions (09-438, 10-318, and 10-321) in which some individuals showed apparent recovery or stem necrosis symptom to a tomato isolate of TSWV-pb1. Thirty-five individuals (one per each accession) which were non-infected by ELISA were selected for further observation. Among these, 26 individuals that did not show any symptom at 5 months after inoculation were confirmed for viral infection by RT-PCR. TSWV-specific PCR amplicon was weakly detected in all 26 individuals including 'Eureta', a commercial F1 possessing the resistance allele of Sw5-b. The resistant genes in the selected individuals may play an important role for reducing the viral concentration in tissues of inoculated tomato plants and seems to be quantitatively controlled by several factors including Sw5-b gene.

• Research in Plant Disease
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• v.21 no.3
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• pp.243-249
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• 2015

Soybean frogeye leaf spot caused by the fungus Cercospora sojina Hara, has known to lead a severe reduction of crop yield. Since frogeye leaf spot on soybean has recently become a serious problem in Korea, the susceptibility of recent recommended cultivars against C. sojina had been tested. To standardize the disease severity of soybean, the optimum sporulation condition of C. sojina and the disease index were established in this study. Sporulation was maximized on the 10% V8 juice agar with 12 h light and 12 h dark at $25^{\circ}C$. Spore suspension ($10^5spores/ml$) was sprayed on the leaves of soybean (V6 stage), and the disease responses to each isolate were evaluated on 28 days after inoculation. As a result, Daepung, Shinpaldal2ho, Yeonpung and Cheonga showed the resistance reaction to 8, 7, 6, 6 isolates of C. sojina, respectively, whereas Cheongja, Hwangkeum, Taekwang, Daewon, Cheonsang and Sinhwa showed the susceptible reaction to 8 isolates of C. sojina. Breeding the resistant soybean cultivars against C. sojina requires a uniform resistance for screening technique. The disease index of frogeye leaf spot on soybean developed in this study can be effectively used for the accurate field assay to select the frogeye leaf spot resistant soybean.