• Journal of Microbiology and Biotechnology
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• v.25 no.6
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• pp.903-909
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• 2015

Indole-3-acetic acid (IAA) production is a typical mechanism of plant growth promotion by some rhizobacteria. However, a functional genomic study is necessary to unravel the function and mechanism of IAA signaling during rhizobacteria-plant interactions. In this study, the expression of SlIAA1 and SlIAA9 among the auxin response genes in tomato was examined during the interaction between IAA-producing Acinetobacter guillouiae SW5 and tomato plants. When 3-day grown tomato seedlings were treated for 30 min with 10~100 µM of IAA produced by bacteria from tryptophan, the relative mRNA levels of SlIAA1 and SlIAA9 increased significantly compared with those of the control, demonstrating that IAA produced by this bacterium can induce the expressions of both genes. Inoculation of live A. guillouiae SW5 to tomato seedlings also increased the expressions of SlIAA1 and SlIAA9, with more mRNA produced at higher bacterial density. In contrast, treatment of tomato seedlings with dead A. guillouiae SW5 did not significantly affect the expression of SlIAA1and SlIAA9. When 3-day bacterial culture in tomato root exudates was administered to tomato seedlings, the relative mRNA level of SlIAA1 increased. This result indicated that the plant may take up IAA produced by bacteria in plant root exudates, which may increase the expression of the auxin response genes, with resulting promotion of plant growth.

• Korean Journal of Microbiology
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• v.50 no.4
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• pp.302-307
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• 2014

Many rhizobacteria can promote plant growth through various direct or indirect mechanisms, and their production of phytohormones such as indole-3-acetic acid (IAA) may have pronounced effects on growth and development of plants. Rhizobacterial strain isolated from rhizosphere of foxtail (Setaria viridis), Acinetobacter sp. SW5 produced 118.1 mg/L of IAA and 4.5 mg/L of gibberellin ($GA_3$) in brain heart broth medium at 2 and 1 day of incubation, respectively. In a pot test the lengths of stem and root and fresh weight of the germinated tomato seedlings treated with Acinetobacter sp. SW5 significantly increased by 26.3, 33.3, and 105.3%, respectively compared to those of the uninoculated control in 12 weeks of cultivation. When the root exudate secreted from tomato seedlings was analyzed by HPLC, 3.75 ng mg tomato $root^{-1}$ of tryptophan which is an IAA precursor was detected. Acinetobacter sp. SW5 could produce $4.06{\mu}M$ of IAA from root exudate from 8 tomato seedlings. Together with the capability of growth of Acinetobacter sp. SW5 in the tomato root exudates, this IAA secreted by bacteria might contribute to enhance the growth of tomato plants.

• The Plant Pathology Journal
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• v.35 no.4
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• pp.362-371
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• 2019

Plant phenotype is affected by a community of associated microorganisms which requires dissection of the functional fraction. In this study, we aimed to culture the functionally active fraction of an upland soil microbiome, which can suppress tomato bacterial wilt. The microbiome fraction (MF) from the rhizosphere of Hawaii 7996 treated with an upland soil or forest soil MF was successively cultured in a designed modified M9 (MM9) medium partially mimicking the nutrient composition of tomato root exudates. Bacterial cells were harvested to amplify V3 and V4 regions of 16S rRNA gene for QIIME based sequence analysis and were also treated to Hawaii 7996 prior to Ralstonia solanacearum inoculation. The disease progress indicated that the upland MM9 $1^{st}$ transfer suppressed the bacterial wilt. Community analysis revealed that species richness was declined by successive cultivation of the MF. The upland MM9 $1^{st}$ transfer harbored population of phylum Proteobacteria (98.12%), Bacteriodetes (0.69%), Firmicutes (0.51%), Actinobacteria (0.08%), unidentified (0.54%), Cyanobacteria (0.01%), FBP (0.001%), OD1 (0.001%), Acidobacteria (0.005%). The family Enterobacteriaceae of Proteobacteria was the dominant member (86.76%) of the total population of which genus Enterobacter composed 86.76% making it a potential candidate to suppress bacterial wilt. The results suggest that this mixed culture approach is feasible to harvest microorganisms which may function as biocontrol agents.

• Korean Journal of Weed Science
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• v.30 no.4
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• pp.412-420
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• 2010

Weeds are known to cause enormous losses due to their interference in agro ecosystems. Because of environmental and human health concerns, worldwide efforts are being made to reduce the heavy reliance on synthetic herbicides that are used to control weeds. In this regard phytotoxicity of allelochemical sorgoleone, which is a major component of the hydrophobic root exudates of Sorghum bicolor was evaluated in different weed species and also its crop selectivity in greenhouse and field conditions. Sorgoleone strongly inhibited the growth of different weeds by pre-emergence and post-emergence applications both in greenhouse and field conditions. Post-emergence application of sorgoleone on 21-day-old weed seedlings had a greater inhibitory effect than the pre-emergence application. Again, broadleaf weed species were more susceptible than grass species to the application of sorgoleone at both stages of growth. Growth of broadleaf weed species was suppressed by greater than 80% for most of the weed species except a few species and among them the species Rumex japonicus and Galium spurium were completely suppressed at $200{\mu}g\;ml^{-1}$ sorgoleone. Like greenhouse trial, sorgoleone was more effective for broadleaf weed species followed by sedge and grass weed species in the field condition. The growth inhibition of weeds was slightly lower in field condition compared to greenhouse condition. The crop species like rice, barley, wheat, corn, perilla, tomato, soybean and Chinese cabbage were tolerant to sorgoleone while lettuce and cucumber were slightly susceptible to sorgoleone. Consequently, sorgoleone may be applied to control weeds in organic farms without affecting the growth of crop.