• Research in Plant Disease
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• v.24 no.4
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• pp.328-331
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• 2018

A severe disease with leaf spots and necrotic symptoms was observed in cucumber (Cucumis sativus L.) seedlings in April 2018 at a nursery in Kimjae, Korea (35o 47'09.8"N 127o 2'24.3"E). The infected plants initially showed spots on water-soaked cotyledons which, at later stages, enlarged and spread to the leaves, which the lesions becoming dry and chlorotic. The symptomatic samples were collected from cucumber and the isolates were cultured on LB agar. The representative bacterial strain selected for identification showed fluorescent on King's medium B, was potato rot-positive, levan and arginine dihydrolase-negative, oxidase-negative and tobacco hypersensitivity-positive in LOPAT group 2 as determined by LOPAT tests. A pathogenicity test was carried out on a 3-week-old cucumber. After 3 days of inoculation, leaf spots and necrotic symptoms appeared on the cucumber, similar to the originally infected plants. The infecting bacterial strain was identified as Pseudomonas viridiflava, by 16S rDNA sequence analysis. This is the first report of leaf spot diseases on cucumber caused by P. viridiflava.

• Research in Plant Disease
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• v.11 no.2
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• pp.135-139
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• 2005

Bacterial canker of Japanese apricot (Prunus mume Sieb. et Zucc.) was found in all orchards located at southern area of Korea. Typical symptoms were characterized by dark spots formed on fruits, brown lesions on leaves, and bacterial exudate oozed out of the cracked bark of diseased tree. Thirty-eight isolates from 16 different areas were identified on the basis of biochemical and physiological characteristics (LOPAT and GATTa test) and also on the basis of 165 rDNA and ITS sequences. Pathogenicity tests confirmed that bacterial canker of Japanese apricot in Korea is caused by Pseudomonas syringae pv. morsprunorum.

• Research in Plant Disease
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• v.22 no.3
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• pp.158-167
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• 2016

A pathogen that causes a new disease on green pumpkin in the nursery and the field was characterized and identified. Symptoms of the disease on green pumpkin were water soaking lesions and spots with strong yellow halo on leaf, brown lesion on flower, and yellow spot on fruit. The bacterial isolates from the leaf spot were pathogenic on the 8 curcubitaceae crop plants, green pumpkin, figleaf gourd, wax gourd, young pumpkin, zucchini, cucumber, melon, and oriental melon, whereas they did not cause the disease on sweet pumpkin and watermelon. They were Gram-negative, rod shape with polar flagella, fluorescent on King's B agar and LOPAT group 1a by LOPAT test. Their Biolog substrate utilization patterns were similar to Pseudomonas syringae pv. syringae's in Biolog database. Phylogenetic trees with 16S rRNA gene sequences and multilocus sequence typing (MLST) with nucleotide sequences of 4 housekeeping genes, gapA, gltA, gyrB, rpoD and those of P. syringae complex strains in the Plant Associated and Environmental Microbes Database (PAMDB) showed that the green pumpkin isolates formed in the same clade with P. syringae pv. syringae strains. The clade in MLST tree was in the genomospecies 1 group. The phenotypic and genotypic characteristics suggested that the isolates from green pumpkin lesion were P. syringae pv. syringae.

• The Plant Pathology Journal
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• v.39 no.1
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• pp.88-107
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• 2023

In the present investigation, bacterial isolates from infected apple trees causing apple canker during winter were studied in the northern Gyeongbuk Province, Korea. The pathogen was identified as Pseudomonas syringae pv. syringae (Pss) through various physiological and biochemical characterization assays such as BIOLOG, gas chromatography of fatty acid methyl esters, and 16S rRNA. Bioassays for the production of phytotoxins were positive for syringopeptin and syringomycin against Bacillus megaterium and Geotrichum candidum, respectively. The polymerase chain reaction (PCR) method enabled the detection of toxin-producing genes, syrB1, and sypB in Pss. The differentiation of strains was performed using LOPAT and GATTa tests. Pss further exhibited ice nucleation activity (INA) at a temperature of -0.7℃, indicating an INA⁺ bacterium. The ice-nucleating temperature was -4.7℃ for a non-treated control (sterilized distilled water), whereas it was -9.6℃ for an INA^- bacterium Escherichia coli TOP10. These methods detected pathogenic strains from apple orchards. Pss might exist in an apple tree during ice injury, and it secretes a toxin that makes leaves yellow and cause canker symptoms. Until now, Korea has not developed antibiotics targeting Pss. Therefore, it is necessary to develop effective disease control to combat Pss in apple orchards. Pathogenicity test on apple leaves and stems showed canker symptoms. The pathogenic bacterium was re-isolated from symptomatic plant tissue and confirmed as original isolates by 16S rRNA. Repetitive element sequence-based PCR and enterobacterial repetitive intergenic consensus PCR primers revealed different genetic profiles within P. syringae pathovars. High antibiotic susceptibility results showed the misreading of mRNA caused by streptomycin and oxytetracycline.

• Research in Plant Disease
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• v.27 no.4
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• pp.180-186
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• 2021

Typical bacterial symptoms, water-soaking brown and black leaf spots with yellow halo, were observed on watermelon seedlings in nursery and field of Gyeongnam and Jeonnam provinces. Bacterial isolates from the lesion showed strong pathogenicity on watermelon and zucchini. One of them was rod-shaped with 4 polar flagella by observation of transmission electron microscopy. They belonged to LOPAT group 1. The phylogenical trees with nucleotide sequences of 16S rRNA and multi-locus sequencing typing with the 4 house-keeping genes (gapA, gltA, gyrB, and rpoD) of the isolates showed they were highly homologous to Pseudomonas syringae pv. syringae and grouped together with them, indicating that they were appeared as P. syringae genomospecies group 1. Morphological, physiological, and genetical characteristics of the isolates suggested they are P. syringae pv. syringae. We believe this is the first report that P. syringae pv. syringae caused leaf spot disease on watermelon in the Republic of Korea.

• The Plant Pathology Journal
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• v.18 no.4
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• pp.199-203
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• 2002

Soft rot occurred severely in onion bulbs stored under low temperature ($5^{\circ}C$) in storage houses at Changyoung, Kyungnam province, Korea in early 2000. Water-soaking and yellowish-brown lesions initially appeared on the outside scales of diseased onion bulbs, gradually progressing into the inside scales. Among the bacterial isolates obtained from the lesions, K-2 isolate was found to be responsible for the disease, which grew at a temperature range of from $0^{\circ}C$ to $36^{\circ}C$ with optimum temperature of $00^{\circ}$-$33^{\circ}C$. However, it showed strong pathogenicity to onion bulbs at $25^{\circ}C$ and $5^{\circ}C$ at 3 days and 2 months, respectively. The bacterium also caused soft rot on potato and showed hypersensitive reactions to tobacco and potato. The causal bacterium of onion soft rot was identified as Pseudomonas marginalis based on morphological, biochemical, and physiological characteristics including LOPAT, Soft rot in onion under low temperature storage caused by P. marginalis has not been previously reported.