• Research in Plant Disease
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• v.24 no.3
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• pp.221-232
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• 2018

Rhizobacteria play important roles in plant growth and health enhancement and render them resistant to not only biotic stresses but also abiotic stresses, such as low/high temperature, drought, and salinity. This study aimed to select plant growth promoting rhizobacteria (PGPR) with the capability to mitigate biotic and abiotic stress effects on tomato plants. We isolated a novel PGPR strain, Variovorax sp. PMC12 from tomato rhizosphere. An in vitro assay indicated that strain PMC12 produced ammonia, indole-3-acetic acid (IAA), siderophore, and 1-aminocyclopropane-1-carboxylic acid (ACC) deaminase, which are well-known traits of PGPR. The aboveground fresh weight was significantly higher in tomato plants treated with strain PMC12 than in non-treated tomato plants under various abiotic stress conditions including salinity, low temperature, and drought. Furthermore, strain PMC12 also enhanced the resistance to bacterial wilt disease caused by Ralstonia solanacearum. Taken together, these results indicated that strain PMC12 is a promising biocontrol agent and a biostimulant to reduce the susceptibility of plants to both abiotic and biotic stresses.

• Proceedings of the Korean Society of Crop Science Conference
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• 2017.06a
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• pp.231-231
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• 2017

Drought limits rice production under upland condition. This study quantified the effect of rhizobacteria inoculation on rice root system developmental response to drought and its role in maintaining high soil water use, and dry matter production under drought using NSIC Rc192 (rainfed lowland rice variety). The source of inoculant was Streptomyces mutabilis, a recently isolated rhizobacteria containing plant growth promoting compounds such as ACC deaminase, indole-3-acetic acid and phosphatase (Cruz et al., 2014, 2015). In the first experiment, pre-germination inoculation of seeds with S. mutabilis significantly increased the shoot and root (radicle) length as well as root hair lengths, relative to the non-inoculated control. In the second experiment, rice plants inoculated with S. mutabilis and grown in rootbox with soil generally had greater total root length under drought regardless of the timing of inoculations, relative to the non-inoculated control. Consequently, improved root system development contributed to the increase in soil water uptake under drought and thus, dry matter production. Among inoculation treatments, one-time inoculation of S. mutabilis either at pre-germination or pre-drought stress at 14 days after sowing (DAS), had significantly greater shoot dry matter production than three-time inoculation at pre-germination, at thinning (3 DAS) and at pre-drought (14 DAS). This study demonstrated the effectiveness of rhizobacteria (S. mutabilis) containing growth promoting compounds for enhancing drought dehydration avoidance root traits and improving the growth of rice plants under drought condition.

• Research in Plant Disease
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• v.25 no.3
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• pp.136-142
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• 2019

Drought stress is considered as one of major abiotic stresses; it leads to reduce plant growth and crop productivity. In this study, we selected bacterial strains for alleviating drought stress in chili pepper plants. As drought-tolerant bacteria, 28 among 447 strains were pre-selected by in vitro assays including growth in drought condition with polyethylene glycol and plant growth-promoting traits including production of 1-aminocyclopropane-1-carboxylate deaminase, indole-3-acetic acid and exopolysaccharide. Sequentially, 7 among pre-selected 28 strains were screened based on relative water content (RWC); GLC02 and KJ40, among seven strains were finally selected by RWC and malondialdehyde (MDA) in planta trials under an artificial drought condition by polyethylene glycol solution. Two strains GLC02 and KJ40 reduced drought stress in a natural drought condition as well as an artificial condition. Strains GLC02 or KJ40 increased shoot fresh weight, chlorophyll and stomatal conductance while they decreased MDA in chili pepper plants under a natural drought condition. However, two strains did not show biocontrol activity against diseases caused by Phytophthora capsici and Xanthomonas campestris pv. vesicatoria in chili pepper plants. Taken together, strains GLC02 or KJ40 can be used as bio-fertilizer for alleviation of drought stress in chili pepper plants.

• Microbiology and Biotechnology Letters
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• v.49 no.3
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• pp.391-402
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• 2021

Earthworms play an important role in soil fertilization, interacting continually with microorganisms. This study aims to demonstrate the existence of beneficial microorganisms living in the earthworm's immune system, the coelomic fluid. To achieve this goal, a molecular identification technique was performed, using cytochrome c oxidase I (COI) barcoding to identify abundant endogenic earthworms inhabiting the temperate zone of Rabat, Morocco. Then, 16S rDNA and ITS sequencing techniques were adopted for bacteria and fungi, respectively. Biochemical analysis, showed the ability of bacteria to produce characteristic enzymes and utilize substrates. Qualitative screening of plant growth-promoting traits, including nitrogen fixation, phosphate and potassium solubilization, and indole acetic acid (IAA) production, was also performed. The result of mitochondrial COI barcoding allowed the identification of the earthworm species Aporrectodea molleri. Phenotypic and genotypic studies of the sixteen isolated bacteria and the two isolated fungi showed that they belong to the Pseudomonas, Aeromonas, Bacillus, Buttiauxella, Enterobacter, Pantoea, and Raoultella, and the Penicillium genera, respectively. Most of the isolated bacteria in the coelomic fluid showed the ability to produce β-glucosidase, β-glucosaminidase, Glutamyl-β-naphthylamidase, and aminopeptidase enzymes, utilizing substrates like aliphatic thiol, sorbitol, and fatty acid ester. Furthermore, three bacteria were able to fix nitrogen, solubilize phosphate and potassium, and produce IAA. This initial study demonstrated that despite the immune property of earthworms' coelomic fluid, it harbors beneficial microorganisms. Thus, the presence of resistant microorganisms in the earthworm's immune system highlights a possible selection process at the coelomic fluid level.

• Journal of Ginseng Research
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• v.45 no.2
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• pp.218-227
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• 2021

Background: Panax ginseng is one of the most important medicinal plants and is usually harvested after 5 to 6 years of cultivation in Korea. Heavy metal (HM) exposure is a type of abiotic stress that can induce oxidative stress and decrease the quality of the ginseng crop. Siderophore-producing rhizobacteria (SPR) may be capable of bioremediating HM contamination. Methods: Several isolates from ginseng rhizosphere were evaluated by in vitro screening of their plant growth-promoting traits and HM resistance. Subsequently, in planta (pot tests) and in vitro (medium tests) were designed to investigate the SPR ability to reduce oxidative stress and enhance HM resistance in P. ginseng inoculated with the SPR candidate. Results: In vitro tests revealed that the siderophore-producing Mesorhizobium panacihumi DCY119^T had higher HM resistance than the other tested isolates and was selected as the SPR candidate. In the planta experiments, 2-year-old ginseng seedlings exposed to 25 mL (500 mM) Fe solution had lower biomass and higher reactive oxygen species level than control seedlings. In contrast, seedlings treated with 10⁸ CFU/mL DCY119^T for 10 minutes had higher biomass and higher levels of antioxidant genes and nonenzymatic antioxidant chemicals than untreated seedlings. When Fe concentration in the medium was increased, DCY119^T can produce siderophores and scavenge reactive oxygen species to reduce Fe toxicity in addition to providing indole-3-acetic acid to promote seedling growth, thereby conferring inoculated ginseng with HM resistance. Conclusions: It was confirmed that SPR DCY119^T can potentially be used for bioremediation of HM contamination.