• The Plant Pathology Journal
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• v.22 no.3
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• pp.248-254
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• 2006

Pear black necrotic leaf spot (PBNLS) on pear trees (Pyrus pyrifolia) is caused by a Korean isolate of Apple stem grooving virus (ASGV-K). Yellow spots were detected in Phaseolus vulgaris (kidney bean) and Chenopodium quinoa which were grown near the diseased pears in year 2000 through 2003. The ASGV-K, the causative agent of PBNLS, was detected from the symptoms of the diseased kidney bean plant and C. quinoa. ASGV-harboring fungi were also isolated from symptomatic plants and from soils surrounding the infected plants. The ASGV-harboring fungus was identified and characterized as Talaromyces flavus. Ecopathological studies showed that the number of ASGV-harboring fungi on the pear leaves was not correlated with differences in temperature or severity of symptoms. Additionally, there was no difference in fungus frequency among the orchard locations or different host plants. Although the frequency of fungi isolated from the soil was not affected by changes in temperature or location, the fungi occurred at higher densities in the rhizosphere than in the plants themselves.

• The Plant Pathology Journal
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• v.22 no.3
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• pp.255-259
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• 2006

The pathogenicity to pear trees and other experimental hosts of the Apple stem grooving virus Korean isolate (ASGV-K) carried by a fungal vector, Talaromyces flavus was examined. ASGV-harboring T. flavus induced mild symptoms on virus-free pears. Symptom severity was intermediate between pears showing typical PBNLS and virus-free pears. Ten cultivars of Phaseolus vulgaris showed 35%-90% infectivity by direct infiltration into leaves and roots by ASGV-harboring T. flavus. Application of fungal cultures to soils showed 0%-70% infectivity depending on the P. vulgaris cultivar. Sap extracted from ASGV-infected Chenopodium quinoa induced similar symptoms on P. vulgaris at 25 days after inoculation. Similar symptoms were also detected on P. vulgaris which were inoculated with ASGV-harboring T.flavus. When healthy P. vulgaris leaves were challenged with sap extracted from P. vulgaris leaves infected with ASGV-harboring T. flavus, typical symptoms were observed. These data suggest that T. flavus mediates the transfer of ASGV to host plants.

• Korean Journal Plant Pathology
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• v.12 no.3
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• pp.368-373
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• 1996

배나무잎 검은점병에 이병된 신고와 지표식물 PS-95의 잎을 전자현미경으로 세포내 미세구조를 검경한 결과 굴곡성 사상형 유사바이러스 입자가 집단으로 존재하고 있는 것을 확인하였다. 엽육유세포질에 있는 유사바이러스 입자들의 직경은 12 nm였으나 입자들의 길이는 측정하지 못하였다. 섬유사를 함유하고 있는 소포는 일반적으로 ssRNA genome을 갖는 식물바이러스에 의해 이병된 세포에서 생성된다. 본 연구에서 이 소포들은 tonoplast에 형성되었다. 배나무잎 검정점병의 이병잎을 초본 지표식물에 즙액접종하였으나 어떠한 병징도 나타나지 않았다. 또한 접목접종 전염에 의하여 전염되어 전형적인 검은점이 발병하였다. 발병된 잎에는 유사바이러스 입자가 존재하고 있었다. 이상의 결과 병징, 섬유사를 함유한 소포의 존재, 그리고 접목전염을 기초로하여 볼 때 배나무 검은점병을 일으키는 유사바이러스 입자는 closteroviruses의 하나로 생각된다.

• The Plant Pathology Journal
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• v.18 no.6
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• pp.301-307
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• 2002

Graft transmission and cytopathological studies of a severe pear disease, pear black necrotic leafspot（PBNLS), were carried out to determine the causal agent of the disease. No evidence was found that a fungal or bacterial pathogen could be the causal agent of the disease. Attempts to transmit the agent by sap-inoculation to other plants including herbaceous hosts failed. How-ever, the pathogen was readily graft-transmitted from symptomatic diseased pears to healthy pears. Graft transmission of the pathogen was also demonstrated by using an indicator plant, PS-95, developed in the laboratory through various grafting methods. Ultrastructural study of the disease revealed the consistent presence of flexuous rod-shaped virus-like particles (VLP) in the symptomatic leaves of both Niitaka cultivar and indicator pear, PS-95. The particles, approximately 12 nm in diameter with undetermined length, occurred in the cytoplasm of mesophyll parenchyma cells. Cells with VLPs also contained fibril-containing vesicles, which are common in cells infected with plant viruses with ssRNA genome. The vesicles were formed at the tonoplast. Based on the symptomatology, the presence of fibril-containing vesicles, and graft-transmissibility, it is believed that the VLPs that occurred on symptomatic leaves of black necrotic leafspot of pear are viral in nature, possibly those of a capillovirus.

• Research in Plant Disease
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• v.16 no.3
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• pp.326-330
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• 2010

Three pome fruit viruses, Apple chlorotic leaf spot virus (ACLSV), Apple stem grooving virus (ASPV) and Apple stem pitting virus (ASGV) were detected in pear trees (Pyrus pyrifolia) using double antibody sandwich enzyme-linked immunosorbent assay (DAS-ELISA) in Ansung, Naju and Ulsan provinces of Korea. Infection rate of three viruses was 35.2% from 452 leaf samples of the three cultivars of pear trees. Also, each of three viruses was detected by reverse transcription polymerase chain reaction (RT-PCR) for a limited number of samples. Infection rate of three viruses was 86.3% from 233 leaf samples of the three pear cultivars. The virus infection rates by RT-PCR were much higher than ELISA. ASGV was prevailing on pear with 74.2%, whereas ASPV and ACLSV were found in 34.8% and 0.4% of tested samples, respectively. Symptoms caused by ASGV showed black spots of infected Niitaka cultivar leaves. The ACLSV, ASPV and ASGV isolates showed 83~94% sequence identity at a nucleotide level to other pome fruit virus isolates when analyzed by NCBI BLAST. Pome fruit viruses occurring in pear were ACLSV, ASPV and ASGV. This is the first report of pear trees infected ASPV in Korea.

• 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.

• Proceedings of the Korean Society of Plant Pathology Conference
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• 2002.11a
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• pp.113.2-114
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• 2002

• Horticultural Science & Technology
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• v.31 no.4
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• pp.512-516
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• 2013

Pear cultivar 'Sinhwa' (Pyrus pyrifolia var. culta Nakai) was originated from a cross between 'Niitaka' and Whasan' with the aims of improving the fruit quality and the traits of cultivation and of early maturing more than 'Whasan' cultivar at Pear Research Station of National Institute of Horticultural & Herbal Science, Rural Development Administration in 1995. 'Sinhwa' was preliminarily selected in 2004 and named in 2009. The tree shows vigorous growth habit and semi-spread characters like 'Niitaka'. Furthermore, it has a sufficient and well upkeep of the flower bud, so it can be more easily cultivated in orchards. In the flower characteristics, flowering time of 'Sinhwa' is $11^{th}$ April like as maternal parent 'Niitaka'. Also 'Sinhwa' has short of pollen grains, so it is need above two pollinizer cultivars. 'Sinhwa' is highly resistant to black leaf spot (Alternaria kikuchiana) and relatively strong to pear scab (Venturia nashicola) in field condition. The optimum harvest time is around Sep. $15^{th}$ in Naju, which is ahead of 'Whasan' about 10 days in the harvest period. The fruit shape is oblate and fruit skin color is yellowish-brown during harvesting time. The average weight of fruit is 627 g, and the soluble solids content is $13.0^{\circ}Brix$. The flesh is very soft and juicy, and renders good eating quality. Shelf life is about 30 days under the room temperature condition.

• Horticultural Science & Technology
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• v.34 no.4
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• pp.655-661
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• 2016

To develop scab-resistant pear (Pyrus spp.) varieties with fruits that are as crisp and juicy as Asian pears, a cross was made between 'Whangkeumbae' and 'Bartlett' varieties (P. pyrifolia ${\times}$ P. communis) at the Pear Research Institute of the National Institute of Horticultural & Herbal Science, Rural Development Administration, in 1994. Among the 285 seedlings, 'Greensis' was first selected in 2006 for its good eating quality and named in 2012 after regional adaptation tests in nine regions and ten experimental plots from 2007 to 2012. The tree showed a vigorous growth habit and semi-spreading characteristics, like 'Whangkeumbae'. The optimum fruit harvest date was also around Sept. 26 and fruit was round in shape and green in skin color at maturity. Average fruit weight was 470g, and the soluble solids content was $12.4^{\circ}Brix$. The flesh was very crisp and juicy, and had good eating quality. Its' leaf size was similar with 'Bartlett' and smaller than 'Whangkeumbae'. The average of full bloom date of 'Greensis' was determined as Apr. 26, which was six days later than 'Whangkeumbae' and similar with 'Bartlett'. S genotypes of 'Greensis' were identified as $S_4S_e$ by S-allele PCR product sequencing analysis. It seems that the $S_4$ allele was inherited from 'Whangkeumbae' and the Se allele from 'Bartlett'. 'Greensis' displayed strong resistance to scab disease caused by Venturia nashicola, similar to European pear cultivars like 'Beurre Hardy' and, 'Conference'. 'Greensis' was also highly resistant to black leaf spot (Alternaria kikuchiana) in the field

• Horticultural Science & Technology
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• v.29 no.6
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• pp.645-650
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• 2011

Pear cultivar 'Supergold' (Pyrus pyrifolia var. culta Nakai) was originated from the cross between 'Chuwhangbae' and 'Manpungbae' with the aims of improving the fruit quality of 'Chuwhangbae' cultivar at Pear Research Station of National Institute of Horticultural & Herbal Science, Rural Development Administration in 1994. 'Supergold' was preliminarily selected in 2002 and named in 2008. The tree shows a vigorous growth habit and semi-spread characters like as 'Manpungbae'. Furthermore, it has sufficient flowers and carries abundant pollen grains, so it can also be used as a pollinator. 'Supergold' is highly resistant to black leaf spot (Alternaria kikuchiana) in the field condition. The optimum harvest time is around Sep. 11th, which is ahead of 'Whangkeumbae' about 5 days in the harvest period. The fruit shape is oblate and fruit skin color is greenish-white at harvesting time. The average weight of fruit is 570 g, and the soluble solids content is $13.6\;^{\circ}Brix$. The flesh is very soft and juicy, and renders good eating quality. Shelf life is about 6 months under the cold storage condition. To determine the self-incompatibility (SI) genotype of 'Supergold' pear cultivar, it was crossed with other cultivars of which SI genotypes have already known. The result of cross-pollinations of 'Supergold' with other cultivars showed relatively high rates of fruit set from 64.5% to 91.0%, except for the cross with pollens of 'Nijisseiki' that represented only 28.8% of fruiting rate. Although sometimes the stigma of 'Supergold' crossed with 'Hayatama', 'Chojuro', and 'Nijisseiki' showed malformed pollen tube tips, 'Supergold' is generally supposed to have cross-compatibility with all other pollen donor cultivars. It is considered that the S-allele of 'Supergold' is $S_3S_4$, which is based on the result of PCR-RFLP.