Ki Deok Kim

Overexpression of a pepper basic pathogenesis-related protein 1 gene in tobacco plants enhances resistance to heavy metal and pathogen stresses

A pepper gene, CABPR1, which encodes basic pathogenesis-related protein 1, has been reported to be strongly induced after ethephon treatment, wounding, and tobacco mosaic virus infection. The potential role of CABPR1 in tolerance of biotic or abiotic stresses was examined in transgenic Nicotiana tabacum cv. xanthi plants. Overexpression of CABPR1 in tobacco plants enhanced tolerance not only to heavy metal stresses, but also to the oomycete pathogen Phytophthora nicotianae, and the bacterial pathogens Ralstonia solanacearum and Pseudomonas syringae pv. tabaci. RT-PCR revealed that the CABPR1 transgene increased expression of the PR-Q and glutathione S-transferase genes, but decreased expression of the PR-1a and thaumatin genes. Moreover, these transgenic lines exhibited significant decreases in total peroxidase activity and transcription level, suggesting that overexpression of CABPR1 in tobacco cells altered the balance of redox systems. Redox imbalance in transgenic lines may lead to H2O2 accumulation, triggering tolerance to biotic and abiotic stresses.

Overexpression of lipid transfer protein (LTP) genes enhances resistance to plant pathogens and LTP functions in long-distance systemic signaling in tobacco

The lipid signal is essential for the activation of plant defense responses, but downstream components of the signaling pathway are still poorly defined. To investigate the biological functions of pepper lipid transfer protein (LTP), we carried out virus-induced gene silencing (VIGS) in pepper, constitutive expression of CALTPs and grafting experiments in the tobacco plant. Suppression of endogenous CALTPI and CALTPII by VIGS, respectively, resulted in enhanced susceptibility to Xanthomonas campestris pv. vescatoria and pepper mosaic mottle virus in pepper. On the other hand, the constitutive expression of CALTPI and CALTPII genes in tobacco plants showed enhanced resistance to oomycete pathogen, Phytophthora nicotianae and bacterial pathogen, Pseudomonas syringae pv. tabaci. Enhanced resistance is found to be associated with the enhanced CALTP transcript levels in the independent transgenic CALTPI or II tobacco lines. Induced resistance responses in grafted scion leaves revealed that LTP plays a role in long-distance systemic signaling in plants.

The volatile‐producing Flavobacterium johnsoniae strain GSE09 shows biocontrol activity against Phytophthora capsici in pepper

Aims:  Previously, we selected a bacterial strain (GSE09) antagonistic to Phytophthora capsici on pepper, which produced a volatile compound (2,4‐di‐tert‐butylphenol), inhibiting the pathogen. In this study, we identified strain GSE09 and characterized some of the biological traits of this strain in relation to its antagonistic properties against P. capsici. In addition, we examined bacterial colonization on the root surface or in rhizosphere soil and the effect of various concentrations of the volatile compound and strain GSE09 on pathogen development and radicle infection as well as radicle growth.

Root Treatment with Rhizobacteria Antagonistic to Phytophthora Blight Affects Anthracnose Occurrence, Ripening, and Yield of Pepper Fruit in the Plastic House and Field

We previously selected rhizobacterial strains CCR04, CCR80, GSE09, ISE13, and ISE14, which were antagonistic to Phytophthora blight of pepper. In this study, we investigated the effects of root treatment of rhizobacteria on anthracnose occurrence, ripening, and yield of pepper fruit in the plastic house and field in 2008 and 2009. We also examined the effects of volatiles produced by the strains on fruit ripening and on mycelial growth and spore development of Colletotrichum acutatum and Phytophthora capsici in the laboratory, identifying the volatile compounds by gas chromatography-mass spectrometry (GC-MS). In the house tests, all strains significantly (P < 0.05) reduced anthracnose incidence on pepper fruit; strains GSE09 and ISE14 consistently produced higher numbers of pepper fruit or increased the fresh weight of red fruit more than the controls in both years. In the field tests, all strains significantly (P < 0.05) reduced anthracnose occurrence on either green or red pepper fruit; strain ISE14 consistently produced higher numbers or increased fresh weights of red fruit more than the controls in both years. In the laboratory tests, volatiles produced by strains GSE09 and ISE13 only stimulated maturation of pepper fruit from green (unripe) to red (ripe) fruit; the volatiles of certain strains inhibited the growth and development of C. acutatum and P. capsici. On the other hand, GC-MS analysis of volatiles of strains GSE09 and ISE13 revealed 17 distinct compounds in both strains, including decane, dodecane, 1,3-di-tert-butylbenzene, tetradecane, 2,4-di-tert-butylphenol, and hexadecane. Among these compounds, 2,4-di-tert-butylphenol only stimulated fruit ripening and inhibited growth and development of the pathogens. Taken together, strains GSE09 and ISE14 effectively reduced anthracnose occurrence and stimulated pepper fruit ripening and yield, possibly via bacterial volatiles. Therefore, these two strains could be potential agents for controlling Phytophthora blight and anthracnose, and for increasing fruit ripening and yield. To our knowledge, this is the first report of volatiles such as 2,4-di-tert-butylphenol produced by rhizobacteria being related to both fruit ripening and pathogen inhibition.

Digital image analysis to measure lesion area of cucumber anthracnose by Colletotrichum orbiculare

A method was developed using scanned computer images and software programs to measure the lesion area on leaves with cucumber anthracnose caused by Colletotrichum orbiculare. After cucumber plants were inoculated with various concentrations of conidia, lesions on diseased leaves were scanned, manipulated with Adobe Photoshop 6.0, and measured using the blob analysis feature in Matrox Inspector 2.2. The method requires relatively low-cost equipment including a scanner, a personal computer, and two programs: Adobe Photoshop 6.0 and Matrox Inspector 2.2. Because stored images are used, the lesion area can be measured as time permits. Processing the images requires about 3 min per sample. The image assessment accurately detected anthracnose lesions on cucumber leaves and could be applied to other foliar necrotic or spot diseases.

Populations of fungi and bacteria associated with samples of stored rice in Korea.

Stored rice was collected from rice processing complexes of National Agricultural Cooperative Federation of 11 regions in Korea to evaluate the occurrence of fungi and bacteria and to identify the predominant fungi and bacteria to the genus levels. Most rice samples generally produced the higher levels of fungi and bacteria than white rice. The occurrence of fungi and bacteria varied in various locations of Korea. Among fungi observed, Aspergillus spp. and Penicillium spp. were dominant in the samples and Aspergillus spp. were observed more frequently than Penicillium spp. Predominant bacteria from rice and white rice samples tentatively belonged to the Genus Bacillus, Pectobacterium, Pantoea, and Microbacterium according to BIOLOG and FAME analyses. The results of this study showed that rice in Korea was contaminated in a relatively high level by two dominant storage fungi such as Aspergillus spp. and Penicillium spp. In addition, occurrence of mycotoxins in rice by the fungi could be possible and thus it is necessary to control the storage fungi.

Chryseobacterium kwangjuense sp. nov., isolated from pepper (Capsicum annuum L.) root.

The yellow-pigmented, Gram-stain-negative, rod-shaped bacterium KJ1R5(T) was isolated from the root of a pepper plant grown in a field in Kwangju, Korea. Strain KJ1R5(T) was characterized by physiological, biochemical, and molecular genetic analyses. Phylogenetic analyses based on 16S rRNA gene sequences showed that strain KJ1R5(T) was most closely related to members of the genus Chryseobacterium, and that the strain exhibited the highest similarities with type strains of Chryseobacterium vrystaatense (97.0 %) and Chryseobacterium rhizosphaerae (97.1 %). DNA-DNA hybridization reassociation values between strain KJ1R5(T) and type strains of C. vrystaatense KACC 11675(T) and C. rhizosphaerae KACC 14918(T) were 46.9 and 38.4 %, respectively. The DNA G+C content of KJ1R5(T) is 40.2 mol%. The predominant respiratory quinone of KJ1R5(T) was menaquinone MK-6; major cellular fatty acids were iso-C15 : 0, summed feature 3 (C16 : 1ω7c and/or C16 : 1ω6c), iso-C17 : 1ω9c, and iso-C17 : 0 3-OH. On the basis of these phenotypic and genotypic characteristics, the strain significantly differed from representative strains belonging to the genus Chryseobacterium. Thus, we propose that strain KJ1R5(T) represents a novel species of the genus Chryseobacterium, named Chryseobacterium kwangjuense sp. nov. The type strain is KJ1R5(T) (= KACC 13029(T) = JCM 15904(T)).

Characterization of Bacillus luciferensis Strain KJ2C12 from Pepper Root, a Biocontrol Agent of Phytophthora Blight of Pepper

In this study, we characterized the bacterial strain KJ2C12 in relation with its biocontrol activity against Phytophthora capsici on pepper, and identified this strain using morphological, physiological, biochemical, fatty acid methyl ester, and 16S rRNA gene sequence analyses. Strain KJ2C12 significantly (P

Constitutive expression of two pathogenesis-related genes in tomato plants enhanced resistance to oomycete pathogen Phytophthora capsici

The potential role of two pathogen-induced pepper genes, encoding basic pathogenesis-related protein 1 (CABPR1) and ascorbate peroxidase-like 1 (CAPOA1), in tolerance against phytopathogens was examined in transgenic tomato (Lycopersicum esculentum cv. House Momotaro) plants. Polymerase chain reaction and reverse transcription-polymerase chain reaction analyses using gene-specific primers revealed that the pepper CABPR1 and CAPOA1 genes were integrated into the tomato genome. The constitutive expression of CABPR1 and CAPOA1 in the tomato did not exhibit any morphological abnormalities. However, these transgenic tomato plants showed enhanced tolerance to the oomycete pathogen Phytophthora capsici, and very weak resistance to the bacterial pathogen Pseudomonas syringae pv. tomato. These results suggest that overexpression of CABPR1 and CAPOA1 in tomato plants altered their resistance responses to pathogenic attack.

Biocontrol of Phytophthora Blight and Anthracnose in Pepper by Sequentially Selected Antagonistic Rhizobacteria against Phytophthora capsici.

We previously developed a sequential screening procedure to select antagonistic bacterial strains against Phytophthora capsici in pepper plants. In this study, we used a modified screening procedure to select effective biocontrol strains against P. capsici; we evaluated the effect of selected strains on Phytophthora blight and anthracnose occurrence and fruit yield in pepper plants under field and plastic house conditions from 2007 to 2009. We selected four potential biocontrol strains (Pseudomonas otitidis YJR27, P. putida YJR92, Tsukamurella tyrosinosolvens YJR102, and Novosphingobium capsulatum YJR107) among 239 bacterial strains. In the 3-year field tests, all the selected strains significantly (P < 0.05) reduced Phytophthora blight without influencing rhizosphere microbial populations; they showed similar or better levels of disease suppressions than in metalaxyl treatment in the 2007 and 2009 tests, but not in the 2008 test. In the 2-year plastic house tests, all the selected strains significantly (P < 0.05) reduced anthracnose incidence in at least one of the test years, but their biocontrol activities were variable. In addition, strains YJR27, YJR92, and YJR102, in certain harvests, increased pepper fruit numbers in field tests and red fruit weights in plastic house tests. Taken together, these results indicate that the screening procedure is rapid and reliable for the selection of potential biocontrol strains against P. capsici in pepper plants. In addition, these selected strains exhibited biocontrol activities against anthracnose, and some of the strains showed plant growth-promotion activities on pepper fruit.