• Korean Journal of Soil Science and Fertilizer
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• v.31 no.3
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• pp.291-300
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• 1998

A study was carried out to evaluate the effect of different salts and their Quantities on the fluctuation and rhizosphere colonization of soil microorganisms. The results obtained are as follows. The electrical conductivities(ECs) of $KNO_3$, $K_2HPO_4$, KCl and $K_2SO_4$ showed negative correlations to the number of gram positive bacteria and gram negative bacteria : the number of bacteria was significantly decreased in the KCl or $KNO_3$ treated group compared to the $K_2HPO_4$ or $K_2SO_4$ treated group. The highest microorganism density of gram negative bacteria, gram positive bacteria and Fusarium sp. in balanced salts-treated soil was observed at $0.5dS\;m^{-1}$, $2.1dS\;m^{-1}$ and $8.0dS\;m^{-1}$ of EC, respectively. The ratio of bacteria to fungi ratio in balanced salts-treated soil substantially decreased as the EC of soil increased. Ten and thirty days after soil treatment with balanced salts, the ratio of bacteria to fungi decreased to 757-1571 and 89-215, respectively. Root colonization density of Fluorescent Pseudomonas in cucumber and tomato significantly decreased as the EC of soil increased, whereas that of Fusarium sp. increased.

• Research in Plant Disease
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• v.14 no.1
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• pp.32-36
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• 2008

Bacterial wilt caused by Ralstonia solanacearum has become a severe problem on tomato in Korea and no effective control measures are available yet. Pseudomonas species play key roles for the biocontrol of many plant diseases especially in soil. A rhizobacterial population of 150 Pseudomonas strains, isolated from the rhizosphere soil of various plants grown at different sites, was screened for 2,4-diacetylphloroglucinol producing gene (PhlD) by PCR. Two strains (P83 and P84) among them were found to be phlD positive. When the isolates were analysed by 16S rDNA (Sensu Stricto), all isolates yielded amplified products of 1,018bp. Of the 150 isolates of Pseudomonas spp., a bacterial strain P. putida P84 isolated from tomato rhizosphere showed to suppress a wide range of phytopathogenic bacteria in vitro. The best source of carbon for P84 strain were glucose, arabinose, inositol and melibiose. In greenhouse experiments, P84 strain suppressed the development of bacterial wilt in tomato with a control value of 60%.

• Proceedings of the Korean Society of Plant Pathology Conference
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• 2003.10a
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• pp.105.1-105
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• 2003

The Plant growth Promoting rhizobacteria (PGPR), Pseudomonas sp. (A3) and Bacillus sp. (AT33) were isolated from the rhizosphere of Amaranthus blitum collected from soil contaminated with chromium. Both bacterial strains quantitatively reduced hexavalent chromium to trivalent chromium. Pseudomonas sp. broughter greater conversion of Cr6+ in the medium (100％) as compared to Bacillus sp.(62％). Phaseolus mungo seeds inoculated with Pseudomonas sp. or Bacillus sp. were grown under different concentration of chromium. The monitored parameters included elongation of shoot and root, fresh weight, dry weight and concentration of chromium in the shoot and root systems. As compared to non inoculated seedlings those inoculated with A3 and AT33 exhibited better growth.

• Proceedings of the Plant Resources Society of Korea Conference
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• 2003.10b
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• pp.57-57
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• 2003

The plant growth promoting rhizobacteria (PGPR), Pseudomonas sp. (A3) and Bacillus sp. (AT33) were isolated from the rhizosphere of Amaranthus blitum collected from soil contaminated with chromium. Bothbacterial strains quantitatively reduced hexavalent chromium to trivalent chromium. Pseudomonas sp. broughter greater conversion of Cr6+ in the medium (100%) as compared to Bacillus sp.(62%). Phaseolus mungo seeds inoculated with Pseudomonas sp. or Bacillus sp. were grown under different concentration of chromium. The monitoredparameters included elongation of shoot and root, fresh weight, dry weight and concentration of chromium in the shoot and root systems. As compared to non inoculated seedlings those inoculated with A3 and AT33 exhibited better growth.

• Korean Journal Plant Pathology
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• v.2 no.2
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• pp.114-120
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• 1986

Significant reduction in disease severity of bacterial wilt (Pseudomonas solanacearum) on the susceptible tobacco cultivar BY 4 was observed until mid-July in a naturally infested field when bacterial suspensions of avirulent isolate were applied to tobacco root zones at one day before and fourty days after transplanting into the field. However, rapid increase in disease severity after mid-July resulted in the same severity $(70\%)$ as on cultivar BY 4 without the application of the avirulent bacterial suspension at the end of the season. Yield increase in cultivar BY 4 was $35\%$ due to the treatment, resulting in $10\%$ price increase. The suppression me chanism did not appear to be dependent upon the inhibition of the virulent bacterial multiplication by the avirulent bacteria in tobacco rhizosphere soil because of no significant difference in the density of the patho genic bacteria between treated and untreated plant root zones. However. penetration of the virulent bacteria into the root systems and their multiplication in tobacco stem were inhibited remarkably by preinoculation with avirulent one, suggesting that those are related to the suppression of disease incidence.

• The Plant Pathology Journal
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• v.18 no.2
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• pp.57-62
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• 2002

In vivo expression technology (IVET) has been developed to study bacterial gene expression in Salmonella typhimurium during host infection. The expression of selected genes by IVET has been elevated in vivo but not in vitro. The selected genes turned out to be important for bacterial virulence and/or pathogenicity. IVET depends on a synthetic operon with a promoterless transcriptional fusion between a selection marker gene and a reporter gene. The IVET approach has been successfully adapted in other bacterial pathogens and plant-associated bacteria using different selection markers. Pseudomonas putida suppresses citrus root rot caused by Phytophthora parasitica and enhances citrus seedling growth. The WET strategy was adapted based on a transcriptional fusion, pyrBC'-lacZ, in P. putida to study the bacterial traits important far biocontrol activities. Several genes appeared to be induced on P. parasitica hyphae and were found to be related with metabolism and regulation of gene expression. It is likely that the biocontrol strain took a metabolic advantage from the plant pathogenic fungus and then suppressed citrus root rot effectively. The result was parallel with those from the adaptation of IVET in P. fluorescens, a plant growth promoting rhizobacteria (PGPR). Interestingly, genes encoding components for type III secretion system have been identified as rhizosphere-induced genes in the PGPR strain. The type III secretion system may play a certain role during interaction with its counterpart plants. Application of IVET has been demonstrated in a wide range of bacteria. It is an important strategy to genetically understand complicated bacterial traits in the environment.

• Korean Journal of Soil Science and Fertilizer
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• v.32 no.1
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• pp.76-83
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• 1999

Studies were conducted during 2 months from May of 1997 to evaluate the effects of pig manure compost(PMC) on soil microbial flora. To do so, a field experiment of Chinese cabbage(Brassica campestris L.) was conducted in a randomized block design on a sandy loam soil and microbial floral characteristics in soils were analyzed. Treatments to control included the application of PMC at (A) $8Mg\;ha^{-1}$CM-8), (B) $29Mg\;ha^{-1}$(CM-2,9), and (C) $57Mg\;ha^{-1}$(CM-57), and of chemical fertilizer(D) at $320N-80P_2O_5-200K_2O\;kg\;ha^{-1}$(NPK). In each treatment, the rhizosphere and non-rhizosphere soils were tested for the analysis of microbial populations. The populations of bacteria, actinomycetes, and fungi increased in soils with the applications of PMC and chemical fertilizer, but that of Bacillus sp. decreased. However, the population of fluorescent Pseudomonas sp. was reduced in NPK plots only. With increasing application rates of PMC, the number of colony forming units(cfu) of bacteria (Pseudomonas sp. and actinomycetes) and fungi increased. in all PMC-treated plots, the population density peaked at early growth stage for bacteria(including Bacillus sp.), at late growth for fluorscent Pseudomonas sp., and at harvest for fungi and actinomycetes. The rhizosphere effect was greatest for fluorscent Pseudomonas sp. As the application rates of PMC increased, Total N, organic matter, available phosphate, and exchangeable -K, -Ca, and -Mg increased compared to control, but soil pH was lowered. In NPK plots, EC was 3.4-fold and exchangeable K was 5-fold higher than control.

• Korean Journal of Soil Science and Fertilizer
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• v.20 no.2
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• pp.193-197
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• 1987

Associative heterotrophic nitrogen fixing bacteria were identified by immunodiffusion method in the histosphere of Planta-ginaceae, Caryophllaceae, Gramineae, and two types of rice cultivars. Twenty four strains associative heterotrophic bacteria with high ARA (more than 10nmole/tube/hr) were isolated from the histosphere of grasses and rice.* Those strains were related with 8 species of Azospirillum, 11 species of Pseudomonas, 2 species of Klebsiella and 2 species of Agrobacterium. Among them Azospirillum sp. and Pseudomonas sp. were predominant in histosphere of grasses and rice cultivars. From the histosphere of Oryza sativa, and Sagina maxima, the strains of Azospirillum, Pseudomonas, Klebsiella, and Agrobacter were identified while Pseudomonas was identified from Ischaemum anthephoroides, Plantago lanceolata, Miscanthus sacchuriflorum, and only Azospirillum was identified from Zoisia sinica, respectively. Associative nitrogen fixing heterotrophic bacteria were more abundant in the histosphere of Oryza sativa and Sagina maxima than that of other grasses grown in saline and reclaimed saline paddy soil.

• Proceedings of the Korean Society of Soil and Groundwater Environment Conference
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• 2000.11a
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• pp.182-195
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• 2000

Indigenous bacteria from poplar roots (Populus mnadensis var. eugenei, 'Imperial Carolina') and Southern Californian shrub rhizospheres as well as two tree-colonizing Rhizobium strains (ATCC 10320 and 35645) were genetically engineered to express constitutively and stably toluene o-monooxygenase (TOM) from Burkholderia cepacia G4 by integrating the torn locus into the chromosome. The poplar and Rhizobium recombinants degraded trichloroethylene (TCE) at 0.8-2.1 nmol/min.mg protein (initial TCE concentration, 10u M) and competitive against the unengineered hosts in wheat and barley rhizospheres for one month (colonization at 1-23 $\times$ 10$^{5}$ CFU/cm root). In addition, six of these recombinants colonized poplar roots stably and competitively with populations as high as 79 $\pm$ 12% of all rhizosphere bacteria after 28 days (0.2-31 $\times$ 10$^{5}$ CFU/cm root). Furthermore, five of the most-competitive poplar recombinants (e.g., Pb3-1 and Pb5-1 which were identified as Pseudomonas PsK) retained the ability to express TOM for 29 days as 100 $\pm$ 0% of the recombinants detected in the poplar rhizosphere had constitutive expression of TOM.

• Proceedings of the Korean Society of Plant Pathology Conference
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• 1994.06a
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• pp.27-49
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• 1994

Root colonization of biocontrol agents via seed treatment was investigated and a compatible combination, Gliocladium virens G872B and Pseudomonas putida Pf3, in colonizing cucumber rhizosphere was confirmed through the study. Much higher number of fungal and bacterial propagules were detected when two isolates were inoculated together. The presence of Pf3 in root system was greatly helpful to G872B to colonize at root tip. The mechanism of this phenomenon is partially elucidated through the results of in vitro experiments and the observations of scanning electron and fluorescence microscope. Addition of Pf3 cells resulted earlier germination of G872B conidia and increased mycelial growth. And the more number of germinated conidia on seed coat, the more vigorous hypal streching and sporulation on the root surface were observed in coinoculated treatment. The propagules of G872B on the cucumber root when they were challenged against the pathogenic Fusarium oxysporum, were even higher than that of G872B treated alone, and the magnitude of such a difference was getting grater toward the root ip and the population of F. oxysporum on the root was reduced by seed inoculation of G872B. The rhizosphere competence was obviously reflected to disease suppression and plant growth promotion that induced by the given isolate. Green house experiments revealed that the combined treatment provided long-term disease suppression with greater rate and the larger amount of fruit yield than single treatments. Through this study the low temperature growing Pseudomonas fluorescens M45 and MC07 were evaluated to apply them to the winter crops in field or plastic film house. In vitro tests reveal that M45 and MC07 inhibited the mycelial growth of Pythium ultimum, Rhizoctona solani and Phytophthora capsici and enhanced growth of cucumber cotyledon in MS agar. This effect was more pronounced when the bacteria were incubated at 14$^{\circ}C$ than at 27$^{\circ}C$. And disease suppression and plant growth promotion in green house were also superior at low temperature condition. Seed treatment of M45 or soil treatment of MC07 brought successful control of damping-off and enhanced seedling growth of cucumber. The combined treatment of two isolates was more effective than any single treatment.