• The Plant Pathology Journal
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• 제36권3호
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• pp.244-254
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• 2020

Gom-chwi (Ligularia fischeri) is severely infected with Phytophthora drechsleri, the causal organism of Phytophthora root rot, an economically important crop disease that needs management throughout the cultivation period. In the present study, Phytophthora root rot was controlled by using bacterial isolates from rhizosphere soils collected from various plants and screened for antagonistic activity against P. drechsleri. A total of 172 bacterial strains were isolated, of which, 49 strains showed antagonistic activities by dual culture assay. In the seedling assay, six out of the 49 strains showed a predominant effect on suppressing P. drechsleri. Among the six strains, the ObRS-5 strain showed remarkable against P. drechsleri when treated with seed dipping or soil drenching. The ObRS-5 strain was identified as Enterobacter asburiae based on 16S ribosomal RNA gene sequences analysis. The bacterial cells of E. asburiae ObRS-5 significantly suppressed sporangium formation and zoospore germination in P. drechsleri by 87.4% and 66.7%, respectively. In addition, culture filtrate of E. asburiae ObRS-5 also significantly inhibited sporangium formation and zoospore germination by 97.0% and 67.6%, respectively. Soil drenched bacterial cells, filtrate, and culture solution of E. asburiae ObRS-5 effectively suppressed Phytophthora root rot by 63.2%, 57.9%, and 81.1%, respectively. Thus, E. asburiae ObRS-5 could be used as a potential agent for the biological control of Phytophthora root rot infecting gom-chwi.

• 한국식물병리학회지
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• 제14권5호
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• pp.445-451
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• 1998

A severe Phytophthora rot of strawberry caused by a species of Phytophthora has been widely occurred at major cultivation areas of Kimhae on August in 1997. Incidence of the disease was obtained in the range of 69.2~83.6% in surveyed 4 fields and showed an average of 75.2%. A species of Phytophthora was mostly isolated from the crown of infected strawberry plants and all the isolates were identified as P. nicotianae var. nicotianae (=P. parasitica). The fungus showed strong pathogenicity on strawberry by inoculation test. As a result of the leaf inoculation using mycelial disks of the fungus, both leaves and petioles were darkly browned, and were finally blighted. As a result of the root inoculation of zoospore suspension, both roots and crowns were rotten with dark brown. Although the fungus produced sporangia either on V-8 juice agar medium or liquid medium, the sporangia observed on the liquid medium appeared to be broadly turbinate and noncaducous. Moreover the fungus cultured on the liquid medium often produced sporangia having two papilla. The number of zoospores in sporangia was found to be ranged from 3 or 4 to as many as 20 or 25. In addition, the released zoospore from the sporangium became the cystospore during the prolonged culture of the fungus. The sporangia were measured as av. 49$\times$35 ${\mu}{\textrm}{m}$ with l/b ratio of 1.43. All isolates from crowns were heterothallic and A1 mating type since oospores were abundantly formed on clarified V-8 juice agar by dual culture with P. capsici A2 mating type. Aplerotic oospores were sized 24-26 ${\mu}{\textrm}{m}$. Antheridia were always amphigynous and recoreded an average of 12$\times$10 ${\mu}{\textrm}{m}$. Hyphal swlling were easily observed, and terminal or intercalary chlamydospores were abundantly formed on V-8 juice agar as well as in C/Z solution and sized av. 28.2 ${\mu}{\textrm}{m}$. This is the first report of Phytophthora rot of strawberry in Korea.

• The Plant Pathology Journal
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• 제17권3호
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• pp.154-158
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• 2001

A severe root rot of kiwifruit caused by a species of Phytophthora occurred in 1-to 5-year-old vines at the south coast region of Korea in 1997. Infected vines exhibited leaf chlorosis, scorch and defoliation, root and stem rot, and eventual death. The disease was relatively severe in poorly drained lowlands, of which 19 out of 23 fields were damaged by the disease. Meanwhile, only one among 58 upland fields was infected by the disease. Incidence of infected vines reached over 80% in heavily damaged fields and a species of Phytophthora was isolated from inner tissues of roots, stems, and rhizosphere soils of the plants. The causal pathogen was identified as P. drechsleri based on its mycological characteristics. Pathogenicity of the fungus was confirmed by artificial inoculation to seedlings of kiwifruit 'Hayward'. The pathogen was re-isolated from the inoculated plants showing symptoms similar to those observed in the fields. Root rot of kiwifruit caused by P. drechsleri has not been reported previously in Korea.

• 한국식물병리학회지
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• 제13권3호
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• pp.139-144
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• 1997

사과 줄기 밑둥을 썩히는 역병 (collar rot)이 경북의 사과 재배지역에 널리 발생하고 있으며, 충북, 충남, 전북 등의 일부 지역에서도 발생이 확인되었다. 이 역병은 주로 M26이나 M9를 왜성대목으로 사용한 후지품종에 심하게 발생되었는데, 발병율은 포장에 따라 큰 차이를 보이지만 의성, 군위, 예산, 무주 등지의 일부 포장에서는 이병주율이 45~80% 정도로 아주 높았다. 수집된 25 균주의 균학적 특성을 조사 결과 모두 Phytophthora cactorum으로 동정되었는데, 이들은 배지에서나 물 속에서 유두돌기가 뚜렷하며, 계란형의 쉽게 이탈되는 다량의 유주자낭을 형성하였고 짧은 자루 (약 4 ${\mu}m$)를 부착하고 있었다. 자웅동주 균으로 10% clarified V8 배지에서 다량의 난포자를 형성하였는데 모든 장정기는 측착 (paragynous) 하였다. 모든 공시 균주는 5$^{\circ}C$ 이하와 33$^{\circ}C$ 이상에서는 자라지 못하였으며 난포자도 형성되지 않았다. Phytophthora cactorum에 의한 사과 줄기역병은 국내에서 기록된 바가 없어 본 병해를 최초로 보고하는 바이다.

• The Plant Pathology Journal
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• 제17권5호
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• pp.311-314
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• 2001

Phytophthora root rot of lettuce, which has not been reported in Korea before, occurred severely in liquid hydroponic culture. The disease occurred in all seasons and was most severe in summer from June to August, showing over 90% infection rate in some farms. A total of 51 isolates collected from various farms were all identified as Phytophthora drechsleri. The fungus showed strong pathogenicity to lettuce and Chinese cabbage, moderate pathogenicity to cucurbits and tomato, and weak pathogenicity to pepper. However, the fungus was not pathogenic to other leafy vegetables namely: chicory, kale, endive, garland chrysanthemum, spinach beet, and perilla. Among 10 species of Phytophtora inoculated to lettuce, only P. drechsleri and P. cryptogea were found pathogenic.

• 한국식물병리학회지
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• 제13권2호
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• pp.129-131
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• 1997

Occurrence of brown rot was observed on imported orange fruits, and irregular brown spots were appeared as an intial symptom. White colored mycelia were developed rapidly on the surface of the fruits under the humid condition and resulted in rotting of the fruits. The causal organism of brown rot of orange was identified as Phytophthora citrophthora. Most sporangia were nondeciduous, papillate, ovoid, and measured 25.5~51.5$\times$17.9~34.7 ${\mu}{\textrm}{m}$ in size. P. citrophtora was pathogenic on Satsuma mandarin as well as orange. Symptoms were produced 3~7 days after artificial inoculation of sporangia and mycelia mixture on the fruits of orange and Satsuma mandarin, which were similar to those on the naturally infected fruits.

• 한국식물병리학회지
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• 제14권5호
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• pp.458-462
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• 1998

Stem rot symptomof lily caused by Phytophthora was observed in Chilkok, Korea in 1997. Oogonia of Phytophthora were abundantly developed on epidermal tissues of stem and leaves of the diseased plants. The casual fungus was identified as Phytophthora cactorum based on their cultural and morphological characteristics. Sporangia were markedly papillate and the shape was broadly spherical to ovoid both on agar and in water. The size was 28~44$\times$20~28 ${\mu}{\textrm}{m}$ (av. 36~24) and a short pedicel was attached to each sporangium. The fungus was homothallic and oogonia were 28~32 ${\mu}{\textrm}{m}$ (av. 30) in size and slightly yellow. Antheridia were paragynous and spherical or irregularly club shaped. Optimal temperature for mycelial growth was 25~27$^{\circ}C$. The fungus did not grow under 6$^{\circ}C$ and over 34$^{\circ}C$. The fungus was highly pathogenic to three cultivars of lily. Symptom was developed at 4-day after artificial inoculation with zoospores (103 cell/ml) on the stem of lily. The symptom was identical to those produced by natural infection in the field and the plant was blighted within 14 days after inoculation.

• 한국환경농학회지
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• 제15권2호
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• pp.207-216
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• 1996

인공산성비의 pH가 낮아질수록 고추씨의 발아에 걸리는 시간은 단축되었으며 발아율은 향상되었으나 어린 싹에게는 매우 치명적인 영향을 미쳤다. 어린 고추모는 이미 자란 식물체에 비하여 산성비에 훨신 더 민감하게 작용하였다. 산성비의 전형적인 가시피해증상은 잎에 나타나는 흰색 반점이었으며, 빗물의 pH가 낮을수록 더 빨리 더 심하게 나타났다. 고추의 역병은 일반적으로 인공산성비 처리구에서 대조구보다 빨리 발병하였으나, 인공산성비의 pH가 아주 낮을 때는 다른 처리구에 비하여 오히려 병의 발생이 줄어들었다. 인공산성비 처리중에 역병을 접종하였을 때는 처리 전에 접종하였을 때보다 병이 더 빨리, 더 심하게 나타났다. 역병의 발생이 가장 심했던 것은 역병의 접종시기와는 관계없이 pH 4.0 또는 4.5인 빗물을 처리하였을 때였다.

• 한국식물병리학회지
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• 제14권5호
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• pp.402-407
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• 1998

Phytophthora rot on jujube fruit has occurred at several cultivation areas in Kyung-buk and Kyung-nam provinces. Symptoms consisted of brownish to reddish rot on fruits resulting in early drop or mummification. The causal fungus isolated from infected fruits and adjacent leaf stalks was identified as Phytophthora citricola, which has never been reported in Korea. Sporangia were semi-papillate, noncaducous and highly variable in shapes. Plerotic oospores with paragynous antheridia were abundant is single cultures. Sporangia of two isolates were measured as 38-76$\times$20-40 ${\mu}{\textrm}{m}$ and averaged 51.4$\times$27.0 and 55.6$\times$36.0 ${\mu}{\textrm}{m}$. Oogonia were ranged from 26 to 36 ${\mu}{\textrm}{m}$ and averaged 31.3 and 32.0 ${\mu}{\textrm}{m}$. Colony pattern was slightly radiated with sparse aerial mycelia on common media. Minium, optimum and maximum temperatures for mycelial growth were recorded at 7, 25, and 32$^{\circ}C$, respectively. Among tested media, 10% V8A was the best and $25^{\circ}C$ was better than 15$^{\circ}C$ for oospore formation of the fungus. The jujube isolates of P. citricola were readily differentiated from other closely related species in the genus, namely; P. nicotianae, P. citrophthora, P. cactorum, P. capsici, and P. plalmivora on the basis of PCR-RFLP of r-DNA. The fungus showed strong pathogenicty to jujube, apple, pear, orange, persimmon and eggplant, and relatively weak to citron, tomato, pepper and cucumber. In this study, P. citrocola is firstly identified and jujube fruit rot caused by the fungus is recorded as a new disease in Korea.

• The Plant Pathology Journal
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• 제17권4호
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• pp.231-235
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• 2001

From April to May 1998, Phytophthora rot on pear, which has not been reported in Korea before, became an epidemic in the southeast part of the country under abnormally higher temperature and prolonged rainy days. Average temperature was about $3^{\circ}$ higher than in normal years, and 29 days were rainy during the 2 months in the areas surveyed. Over 1,000 orchards estimated at about 270 ha in 19 cultivation areas were infected by the disease, which occurred on all parts of the tree such as leaves, shoots, branches, stems, and flower clusters. Among 43 isolates collected from various locations and plant parts, 41 were identified as Phytophthora cactorum while 2 were identified as P. cambivora based on their mycological characteristics. The representative isolates revealed strong pathogenicity not only to pear but also to apple and peach. Among 23 pear cultivars tested, 7 were estimated as susceptible, 4 were moderate, and 11 were resistant to the pathogen. Results suggest that Phytophthora disease on pear is a potential threat to pear cultivation when environmental factors are favorable to disease development.