• Research in Plant Disease
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• v.16 no.2
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• pp.183-190
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• 2010

During the period from 1999 to 2008, we surveyed the major diseases incidence of rice in Korea. Leaf blast showed 0.85% of the diseased leaf area in 2000 and then consistently decreased to 0.02% by 2008. However, panicle blast irregularly appeared by the years depending on weather conditions for disease development from heading to milk stage of rice. Diseased lesion height of sheath blight had the lowest (10.1%) incidence in 2001 and the highest (21.4%) incidence in 2007. A negative corelation ($r=-0.88^*$) was measured between diseased lesion height of sheat blight and sunshine hours from mid- to late August. In Chunbuk, Gyeongbuk, and Gyeongnam provinces, brown spot occurrence declined since 2001, however, in Chungnam, Jeonbuk, and Jeonnam provinces, it increased since 2005. False smut drastically decreased after showing the highest incidence of 7.59% in panicles in 2000. The correlation coefficient between diseased panicles of false smut and rainfall during the late August was calculated as $0.94^{**}$. Bacterial leaf blight severely increased in the chronically infested fields in Jeonnam, Jeonbuk, Gyeongnam, and Chungnam province since 2003.

• Research in Plant Disease
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• v.18 no.2
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• pp.133-138
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• 2012

In November 2009, a powdery mildew on glossy abelia (Abelia ${\times}$ grandiflora) was found in Seogwipo, Jeju Island, Korea. Further survey in the southern part of Korea, e.g., Jeju, Busan, and Tongyeong confirmed occurrence of the disease. White colonies were present on leaves, young stems, and flowers, detracting from their beauty in landscape plantings. Severely infected lesions were discolored to red-purplish. Based on the morphological characteristics and analysis of rDNA, the fungus associated with the symptoms was identified as Erysiphe abeliicola U. Braun & S. Takam. This work provides the morphological feature of its anamorph for the first time, which is characterized by having multi-lobed hyphal appressoria and short foot-cells of conidiophores. Morphological characteristics of mature chasmothecia were consistent with the previous Japanese record of this species. The sequence of internal transcribed spacer region of ribosomal DNA obtained from a Korean sample showed that this species places in the section Microsphaera of the genus Erysiphe in phylogenetic position, corresponding with the classical taxonomy. This is the first report of E. abeliicola and its host plant in Korea. The host plant A. ${\times}$ grandiflora is newly listed in the host range of E. abeliicola.

• Korean Journal Plant Pathology
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• v.2 no.1
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• pp.31-36
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• 1986

The symptom of anthracnose of chinese matrimony vine (Lycium chinense Mill) was darkbrown to black, water­soaked lesions with acervuli on fruits. Field survey revealed that the incidence rate of anthracnose ranged from $0.8\%\;to\;23\%$. to Colletotrichum gloeosporioides Penz and C. dematium(Fr.) Grove were identified as the causal organisms of the disease. C. gloeosporioides and C. dematium produced severe symptoms on fruits resulting in complete necrosis, but produced no or mild symptoms on leaves and stems of chinese matrimony vine. Of three isolates of C. dematium, isolate I and isolate III caused severe infection on immature fruits and isolate I was the most pathogenic on mature fruits of the plant. Isolates II of C. dematium caused relatively severe lesions on pepper fruit, but C. gloeosporioides was pathogenic on apple fruit.

• Research in Plant Disease
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• v.23 no.1
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• pp.82-87
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• 2017

During 2012 to 2014, a survey for the presence of viral diseases in yam plants was carried out in a field of the Institute for Bioresources Research in Gyeongsangbuk-do, Korea. A total of 88 leaf samples were collected and tested by reverse transcription polymerase chain reaction using specific primer sets. Eighty-one samples were positive for Broad bean wilt virus 2 (BBWV2), Chinese yam necrotic mosaic virus (ChYNMV), Cucumber mosaic virus (CMV), Japanese yam mosaic virus (JYMV), and Yam mild mosaic virus (YMMV), whereas Yam mosaic virus (YMV) was not detected. Additionally, seven samples were negative for all viruses. Several samples exhibited mixed (double and triple) infections. Three viruses (CMV, JYMV, and YMMV) were detected for the first time in yam plants in Korea. A BLAST search showed that three viruses shared nucleotide identities with CMV-Ca (98%), JYMV-O2 (91%), and YMMV-TG_NH_1 (86%). Thus, our findings confirmed that yam plants cultivated in Korea were infected with multiple viruses with three of these viruses reported for the first time in Korea.

• The Korean Journal of Mycology
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• v.22 no.3
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• pp.229-246
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• 1994

Powdery mildew fungi from 246 different species of host plants were collected at Kangwon province during 1989-1993 years. They were identified and classified into 13 genera and 83 species by examining various morphological characteristics of taxonomic value. Most of host plants were infected with one species of powdery mildew fungus, but eight plant species with two or three different mildews. Among 246 host plants collected, 43 species were added as the new host plants of powdery mildew fungi in Korea. Two Oidium spp. from Hibiscus and several Compositae plants were described to suggest their taxonomic problems.

• Research in Plant Disease
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• v.25 no.1
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• pp.43-47
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• 2019

Apple chlorotic leaf spot virus (ACLSV), Apple stem pitting virus (ASPV), Apple stem grooving virus (ASGV), and Apple scar skin viroid (ASSVd) are economically important viruses that infect pear tree species worldwide. To evaluate the prevalence of these viruses in Korea, we investigated infection degree of three viruses and one viroid for the commercial nursery trees of the pear cultivars, Niitaka, Chuwhang, Wonwhang, and Whasan in 2017 and 2018. The results showed that the infection ratio of ACLSV, ASPV, ASGV, and ASSVd for the scion of pear cultivar Niitaka was 10%, 45%, 77%, and 50%, respectively. From the scion of pear cultivar Chuwhang, infection ratios of ASPV, ASGV, and ASSVd were found to be 70%, 50%, and 60%, respectively. From the scion of pear cultivar Whasan, infection ratios of ACLSV, ASPV, ASGV and ASSVd were found to be 40%, 60%, 93%, and 20%, respectively. From the root stock of pear cultivar Wonwhang, infection ratios of ACLSV, ASPV, ASGV, and ASSVd showed 28%, 57%, 100%, and 14%, respectively. ASGV had the highest recorded infection rate, and ACLSV was characterized by the lowest infection rate. The mixed infection ratio of Niitaka, Chuwhang, Whasan, and Wonwhang was 45%, 60%, 70%, and 85%, respectively.

• Journal of Plant Biotechnology
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• v.49 no.3
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• pp.193-206
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• 2022

Astringent persimmon (Diospyros kaki Thunb.) is an important fruit crop in Korea; it possesses significant medicinal potential. However, knowledge regarding the pathogens affecting this crop, particularly, viruses and viroids, is limited. In the present study, reverse transcription-polymerase chain reaction (RT-PCR) and high-throughput transcriptome sequencing (HTS) were used to investigate the viruses and viroids infecting astringent persimmons cultivated in Korea. A one-step multiplex RT-PCR (mRT-PCR) method for the simultaneous detection of the pathogens was developed by designing species-specific primers and selecting the primer pairs via combination and detection limit testing. Seven of the sixteen cultivars tested were found to be infection-free. The RT-PCR and HTS analyses identified two viruses and one viroid in the infected samples (n = 51/100 samples collected from 16 cultivars). The incidence of single infections (n = 39/51) was higher than that of mixed infections (n = 12/51); the infection rate of the Persimmon cryptic virus was the highest (n = 31/39). Comparison of the monoplex and mRT-PCR results using randomly selected samples confirmed the efficiency of mRT-PCR for the identification of pathogens. Collectively, the present study provides useful resources for developing disease-free seedlings; further, the developed mRT-PCR method can be extended to investigate pathogens in other woody plants.

• The Plant Pathology Journal
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• v.38 no.5
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• pp.482-489
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• 2022

Fire blight caused by Erwinia amylovora (Ea) is a devastating disease in apple and pear trees. Oxolinic acid (OA), a quinolone family antibiotic that inhibits DNA gyrase, has been employed to control fire blight in South Korea since 2015. The continuous use of this bactericide has resulted in the emergence of OA-resistant strains in bacterial pathogens in other countries. To investigate the occurrence of OA-resistant Ea strains in South Korea, we collected a total of 516 Ea isolates from diseased apple and pear trees in 2020-2021 and assessed their sensitivities to OA. We found that all isolates were susceptible to OA. To explore the possibility of emerging OA-resistant Ea by continuous application of OA, we exposed Ea stains to a range of OA concentrations and constructed OA-resistant mutant strains. Resistance was associated with mutations in the GyrA at codons 81 and 83, which result in glycine to cysteine and serine to arginine amino acid substitutions, respectively. The in vitro growth of the mutants in nutrient media and their virulence in immature apple fruits were lower than those of wild-type. Our results suggest that OA-resistance decreases the fitness of Ea. Future work should clarify the mechanisms by which OA-resistance decreases virulence of this plant pathogen. Continuous monitoring of OA-resistance in Ea is required to maintain the efficacy of this potent bactericide.

• Research in Plant Disease
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• v.23 no.2
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• pp.186-192
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• 2017

To survey the incidence of plant-parasitic nematode in strawberry nursery, 117 soil samples were collected from main producing area of strawberry nursery plants in 2016. The incidences of two major problematic nematodes such as root-lesion nematodes (Pratylenchus spp.) and root-knot nematodes (Meloidogyne spp.) were 11% and 3%, respectively. Strawberry nurseries using upland soil either in fields or in plastic-houses showed were higher infection rates of Pratylenchus spp. or Meloidogyne spp. than others. On the other hand, a strawberry nursery using pots filled with bed soil in plastic-house was the lowest infection rate with 0%. Phylogenetic relationships and distance analysis were performed for identification of Pratylenchus spp. and Meloidogyne spp. detected from strawberry nurseries. As the results, they were identified as Pratylenchus penetrans, Pratylenchus vulnus and Meloidogyne hapla. Meanwhile, when nursery plants of strawberry infested with P. vulnus transplanted to pots filled with sterilized soil, P. vulnus was detected from soil in pots as 33% frequency. Thus, P. vulnus can be spread through nursery plants of strawberry infested with that. These studies suggested that Pratylenchus spp. and Meloidogyne spp. were ploblematic nematodes in major areas of strawberry nursery plants and P. vulnus could be spread through nursery plants of strawberry.

• Research in Plant Disease
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• v.20 no.1
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• pp.8-14
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• 2014

The socio-network activities for regional governments, agricultural research institutes, developing agencies and policy makers of any countries are very crucial and important to take into account the root cause of current problems faced by farmers. The survey was conducted in South Korea during the period January, 2008 to August, 2012 in order to shed light on prevalence of different diseases on watermelon in different regions and to better understand farmers' knowledge and perceptions for following watemelon's growing procedures and practices. A total of 590 cases were reported on 573 watermelon growers with highest 87.1% in Jeonbuk, 4.7% in Jeonnam, and 8.2% in other regions such as Gyeongbuk, Gyeongnam, Chungnam, Gwangju, Gyeonggi, Daegu, Gangwon, Changwon and Seoul. The maximum percentages of cases recorded were related to diseases and insect pest (38.6%) followed by physiological disorder (29.7%), cultural practices (18.8%), soil and fertilizer (9.0%), herbicide (2.9%) and others (1.0%). It was observed that the manifestation aspects of the diseases were changed due to increasing in proportion of 'in-facility' cultivation to 12,995 ha compared to 'open-field' cultivation (2,722 ha). The present survey revealed the necessity to reduce the damages incurred at watermelon farms as soon as possible through the breeding program to develop resistant cultivar, use of pathogen-free propagating plants, and efficient prevention of pathogen by regular monitoring of watermelon plants at farms.