Hyeong-Hwan Kim

Screening of Tomato Cultivars Resistant to Bacterial Wilts

Bacterial wilts, caused by Ralstonia solanacearum, is a very destructive disease to tomato plants (Solanum lycopersicum) in Korea. Selection of resistant cultivar is the best way to prevent or reduce the occurrence of this disease. Thirty-nine tomato cultivars, twenty-one cherry tomato cultivars and thirteen rootstock tomato cultivars were inoculated with Ralstonia solanacearum, to evaluate tomato cultivars for resistance against bacterial wilts. Thirty-seven cultivars were highly susceptible to bacterial wilts and 61-100% of their whole tissue became wilted within 10 days after inoculation. Twenty-four cultivars showed moderate resistance and twelve were resistant to bacterial wilts. In an evaluation of 73 major commercial cultivars, ‘Lilyance’, ‘TP-7’, ‘Choice’, ‘Dadaki’, ‘Akiko’, ‘Redstar’, ‘Match’, ‘B-blocking’, ‘Magnet’, ‘Support’, ‘Friend’ and ‘Special’ were found to have a high level of resistance to bacterial wilts of tomatoes.

First Report of Myrothecium roridum Causing Leaf and Stem Rot Disease on Peperomia quadrangularis in Korea

Abstract In 2010, symptoms of leaf and stem rot were observed on potted plants (Peperomia quadrangularis) in a greenhouse in Yongin, Korea. The causative pathogen was identified as Myrothecium roridum based on morphological data, internal transcribed spacer sequence analysis, and pathogenicity test. To our knowledge, this is the first report of M. roridum causing leaf and stem rot disease on P. quadrangularis in Korea and elsewhere worldwide.

Hatchability and Temperature-dependent development of Overwintered Eggs of Ricania sp. (Hemiptera: Ricaniidae)

Ricania sp. lay eggs into the new twigs of blueberry and suck nutrients causing growth retardation and a sooty mold symptom. This study was conducted to investigate the emergence success and developmental period of overwintered eggs of Ricania sp. under the seven constant temperatures from 10 to by intervals (14L:10D). We also monitored the emergence time of the Ricania sp. nymph at blueberry by 3 ~ 4 day interval using a modified leaf clip cage. Development times from the overwintered egg to nymph were 107.1, 54.5, 33.9, 25.3, 25.1 and 16.7 days and the emergence successes were 23.1, 30.8, 13.8, 21.7, 11.9, and 0.6% at 14, 18, 22, 26, 30 and , respectively except at . The developmental periods were decreased with increasing temperatures. First emergence date of the nymphs in the field was between 19 and 22 May, and the average emergence success was 19.6%. The present study might be helpful to establish the management strategy of Ricania sp. based on the biological characteristic.

Screening of Tomato Cultivars Resistant to Root-knot Nematode, Meloidogyne incognita

Horticultural Environment Division, National Institute of Horticultural & Herbal Science, RDA, Suwon 441-440, Korea(Received on November 9, 2010; Accepted on November 19, 2010)Thirty-two tomato cultivars, eleven cherry tomato cultivars and eight rootstock tomato cultivars wereinoculated with Meloidogyne incognita, to evaluate tomato cultivars for resistance against root-knotnematodes. One tomato cultivar, Homerunking was proved to be resistant while eight cultivars such asRegendsummer, Regend, Sunmyung, Pinktop, Top3, Delice, Tasha and Lilyance were moderately resistant tothe root-knot nematodes. Five cherry tomato cultivars (Tenten, Desert, Redstar, Veryking and Arigatto)showed moderate resistance and one cultivar (Redcherry) was resistant to root-knot nematodes. In eightrootstock tomato cultivars, two cultivars (Bukinghagae, Special) were resistant and five cultivars (B-blocking,Solution, Dongbanja and Greenpower) were moderate.Keywords : Egg mass, Meloidogyne incognita, Resistant, Tomato cultivar전 세계적으로 약 500여종의 식물기생성 선충이 보고되어 있고, 뿌리혹선충(Meloidogyne spp.)은 78종이 분포하는 것으로 기록되어 있으며(Jepson, 1987), 국내에서는시설원예재배지에 서식하고 있는 뿌리혹선충으로 땅콩뿌리혹선충(M. arenaria), M. cruciani, 당근뿌리혹선충(M.hapla), M. hispanica, 고구마 뿌리혹선충(M. incognita), 자바니카뿌리혹선충(M. javanica) 등 6종이 알려져 있는데이중에서 땅콩뿌리혹선충, 당근뿌리혹선충, 고구마 뿌리혹선충, 자바니카뿌리혹선충 등 4종이 농업상 중요 뿌리혹선충이다(Cho 등, 2000; Kim 등, 2001).뿌리혹선충은 국내에 재배되고 있는 과채류, 엽채류 및화훼류 등 원예작물 전반에 걸쳐 2령충이 작물에 침입하여 기생하면 구침으로 작물의 조직을 찔러 영양분을 섭취하면서 뿌리에 혹을 형성하게 되어 양분과 수분의 이동을 저해하고, 탈취하므로 지상부의 생육이 불량해진다(Kim, 2001). 또한 뿌리혹선충은 양분과 수분의 흡즙에의한 직접적인 피해뿐만 아니라 선충의 침입에 의해 뿌리혹 주변 세포조직이 와해되어 토양에 서식하는 각종 병원균이 침입하여 이차적으로 토양 전염성 병의 침입을 조장하기도 한다(Park 등, 1995). 우리나라는 공정육묘장의 증가로 대부분의 원예작물 재배 농가에서는 유묘를 자가 육묘하기 보다는 구입하여 사용하고 있어 육묘기에 뿌리혹선충에 의한 감염은 극히 드물어 뿌리혹선충과 접촉하게 되는 것은 정식과 더불어 시작되기 때문에 방제는 대부분 정식 전·후에 행해지고 있다. 뿌리혹선충의 방제 방법에는 답전윤환, 객토, 태양열소독, 약제방제, 저항성 품종, 윤작, 휴경, 재배시기 조절,길항식물과 유치작물 재배, 잔재물 소각, 담수, 기생된 작물 잔재물 제거, 접목, 유기물 토양 개선과 생물적 방제,작물 경작 개선 등과 같이 다양한 방법들이 알려져 있다(Park 등, 1995; Kim, 2001; Kim과 Choi, 2001; Kim과Lee, 2008). 그러나 뿌리혹선충의 종이나 race에 따라 저항성 품종에 대한 반응이 상이하기 때문에 다양한 뿌리혹선충 방제법 중에서도 효과가 높으면서 환경 친화적인

Transmission of Fusarium oxysporum by the Fungus Gnat, Bradysia difformis (Diptera: Sciaridae)

The fungus gnat, Bradysia difformis was examined for its ability to transmit Fusarium oxysporum in PDA culture. Larvae and adults of B. difformis were able to transmit the fungus as ingested and sticking. We constructed GFP-expressed mutants with Fusarium oxysporum, then feed it to larvae of fungus gnat, B. difformis. So that mycelia were placed in the alimentary canal of larva.

Biological Control of Tobacco Cutworm, Spodoptera litura (Lepidoptera: Noctuidae) by Steinernematid and Heterorhabditid Entomopathogenic Nematodes

Five effective strains against tobacco cutworm, Spodoptera litura (Lepidoptera: Noctuidae), Steinernema carpocapsae (GSN1), Steinernema sp. (GSNUS-10), Steinernema sp. (GSNUS-14), Heterorhabditis bacteriophora Hamyang (HbH), and Heterorhabditis sp. (GSNUH-1) were selected among 14 isolates of Korean entomopathogenic nematode in laboratory tests. values of above five strains against tobacco cutworm were various by different nematode strains and developmental stages of tobacco cutworm. value of S. carpocapsae (GSN1) was the lowest by infective juveniles (Ijs) and 2nd instars of tobacco cutworm was most susceptible. Pathogenicity of five effective strains against tobacco cutworm depends on nematode strain, concentration, and application times. The most effective strain was determined as S. carpocapsae (GSN1). Two or three times of applications were effective regardless of nematode strain, or concentration. Efficacy of S. carpocapsae (GSN1), Steinernema (GSNUS-10), Steinernema (GSNUS-14), and Heterorhabditis (GSNUH-1) was variable depending on nematode strain, concentration, application times, and host variety. S. carpocapsae (GSN1) was the most effective and inoculation of 100,000 infective juveniles per m2 (720,000 Ijs/7.2

Microflora of phytopathogen-transferring Bradysia agrestis: a step toward finding ideal candidates for paratransgenesis

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Damages by Tyrophagus similis (Acari: Acaridae) in greenhouse spinach in Korea.

Owing to the effect of symbiotic gut bacteria on the proliferation of infectious disease-transferring insects and their potential as paratransgenic tools, their identification or securing their use in controlling insect vectors is urgently needed. Bradysia agrestis is one of the major plant epidemic vectors in East Asia; however, its normal microbiota remains unstudied. This research was primarily designed to secure promising candidates for use in a paratransgenic approach to phytopathogen control, as well as to provide a picture of the gut microbiota of wild-caught B. agrestis from a blight field. A total of 180 larvae from three different regions in South Korea were analyzed for their gut microfloral composition. Diverse bacterial strains were purely isolated based on morphological differences in microbiological media. We found a total of 64 bacterial strains in the B. agrestis midgut and analyzed their 16S rRNA gene sequences for molecular identification and phylogenetic characterization. Furthermore, the microbial diversity of each normal microbiota group was analyzed with various diversity indices. Bacterial biota including species diversity, richness or species distribution, species constituents, and dominance varied by each regional vector group. The most widely distributed species was Bacillus aryabhattai, and the most common genera were Bacillus and Microbacterium. These saprophytic bacteria were isolated from all regional groups and their potential as paratransgenic candidates for controlling B. agrestis-mediated plant disease is discussed.

Fungal load in Bradysia agrestis, a phytopathogen-transmitting insect vector

A mite damage was observed in spinach (Spinacia oleracea L.) under organic culture greenhouses. The mite was identified as Tyrophagus similis Volgin, 1949. It was very difficult for the farmers to diagnose the mite damage because of its tiny size about 0.5 nm in length. And the symptom was not clear at the early growth stage of the spinach because the mite mainly attack the very young leaves. In this study, we first report the spinach damages by T. similis in Korea. Informations on the mite morphology and the spinach damage symptoms are provided for the diagnosis.

Economic Injury Level of Thrips tabaci (Thysanoptera: Thripidae) on Welsh onions (Allium fistulosum L. var) in the Early Transplanting Stage

Larvae of Bradysia agrestis, a phytopathogen-transmitting insect vector in East Asia, were sampled from geographically (ecologically) segregated regions to identify their intestinal fungal flora. A total of 24 fungal strains were isolated from the insect vectors and selected based on morphological differences. In addition, 38 fungal strains were isolated from the ulcerated parts of invaded host plants by the same method, revealing the impact of vector fungal flora on their host plants. For molecular identification of the fungi, internal transcribed spacer (ITS) regions were amplified and sequenced. Their sequences were compared with sequences of other fungal strains obtained from NCBI GenBank, and their phylogeny was determined. The dominant fungal genera in the insect vector were Penicillium (25%), Aspergillus (21%), and Cladosporium (13%). In plant scar lesions, most fungal isolates belonged to the genera Fusarium (31.6%), Phoma (7.8%), Didymella (7.8%), and Epicoccum (7.8%). Fungal genera in vectors or host plant lesions differed by study site. Furthermore, diversity indices by study site showed clear differences based on Margalef’s richness (2.06, 2.40, 3.04), and Menhinick’s (1.89, 2.12, 2.53), and Simpson’s indices (0.14, 0.07, 0.07). In addition, common fungal strains in insect vectors were found to be closely related to members of the genera Cladosporium, Penicillium, or Aspergillus. Among these strains, those showing the highest homology with Aspergillus terreus, which regarded as beneficial fungal genera could be considered ideal paratransgenesis candidates. Some other fungal strains from vectors or ulcerated plant parts from each study site after B. agrestis invasion may be harmful in terms of plant disease or agrifood safety. This study provides information on the fungal microbiota of B. agrestis, an emerging problem in East Asia, and proposes paratransgenesis candidates to control this insect vector. Furthermore, potential transferable pathogens or commensal fungi were revealed by comparing the fungal biota between the insect gut and the ulcerated parts of the invaded host plants.