• Research in Plant Disease
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• v.30 no.2
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• pp.124-130
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• 2024

Leaf blight caused by Stemphylium vesicarium is one of the most important fungal diseases of garlic (Allium sativum L.) worldwide, which results in a reduction of quality and yield. The breeding of resistant cultivars is an efficient approach to decrease the use of chemical fungicides and minimize crop losses. In this study, to find the resistant garlic resources against S. vesicarium, we evaluated the resistance degree of 20 garlic germplasms. To do this, garlic seedlings at four-leaf stage were rubbed with nonabsorbent cotton and then inoculated with spore suspension (3.0×10⁵ spores/ml of potato dextrose broth) of S. vesicarium by spray method. Three to seven days after inoculation, the infected leaf area (%) of garlic seedling was measured. 'Daeseo' and 'Namdo' were included as susceptible and resistant control cultivars, respectively. After 3 to 7 days of incubation, the infected leaf area (%) of garlic seedling was measured. Our results showed that IT245512, IT245528, and IT244068 lines exhibited the highest resistance against S. vesicarium, whereas IT257134 and IT253043 lines were more susceptible than the susceptible cultivar 'Daeseo'. Based on the results, the resistant genetic resources selected in this study can be used a basic material for resistant garlic breeding system against leaf blight.

• Research in Plant Disease
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• v.30 no.3
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• pp.219-228
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• 2024

Pepper anthracnose, caused by Colletotrichum spp., leads to a decrease in the quantity of pepper fruit production. Molecular diagnosis is crucial for rapid identification of pathogens and determination of fungicide resistance. However, the traditional process of isolating the pathogen, extracting genomic DNA, and analyzing the gene sequence is time-consuming, which delays rapid diagnosis. In this study, we introduced a method using conidia of Colletotrichum spp. instead of genomic DNA, eliminating the need for DNA extraction or special processing for diagnosis. To elucidate this method, sensitivity was assessed through polymerase chain reaction (PCR) and quantitative real-time PCR (qPCR) tests using internal transcribed spacer-based primer pairs. Both PCR and qPCR tests showed that detection is feasible with just one conidia, with over 1,000 conidia yielding results comparable to approximately 1 pg of genomic DNA. For amplifying the cytochrome b gene for quinone-outside inhibitor fungicide susceptibility testing, detection from a single conidium is achievable, but a stable PCR product is obtained by increasing the number of cycles to 35. Additionally, the addition of 10% grinding fresh chili pepper paste to V8-Juicea gar medium, which is known for inducing conidia rapidly from the isolates, resulted in 3.2 to 6.0 times more conidia compared to the commonly used potato dextrose agar medium, enhancing the potential for swift testing. Taken together, this study presents a direct utilization of pepper anthracnose conidia through PCR or qPCR, offering a valuable technique for amplifying target genes, such as the minimum conidial amount and barcode genes, for molecular identification of anthracnose disease in pepper through PCR and qPCR analysis.

• Horticultural Science & Technology
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• v.33 no.6
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• pp.883-890
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• 2015

The soilborne fungus Fusarium oxysporum f. sp. lilii (Fol) is a serious threat to all lily cultivars, especially infecting bulbs and flowers. It has become increasingly important to develop varieties resistant against the bulb rot disease. Genetic diversity of cultivars and reliable screening methods are required for this purpose. Here, an efficient in vitro screening system for evaluating resistance to Fol in 38 in vitro-grown lily plants was investigated. Various factors including culture conditions of Fol, inoculum density, appropriate plant materials, inoculation method and duration, and incubation period of plant materials after inoculation were combined to optimize the screening method. As a result, we suggest optimal conditions for an in vitro screening system for the selection of Fol-resistant lily cultivars as follows. Fol was grown on potato dextrose agar (PDA) medium for 6 days at $25^{\circ}C$ in darkness and used as working inoculation. Spore suspensions were prepared (inoculum density: $1.0{\times}10^4$ $spores{\cdot}mL^{-1}$), and then leaf segments $1.5{\times}2.0cm^2$ were inoculated by dipping for 22 hours at $25^{\circ}C$ in dark. Later, leaves were cultured on 0.6% agar plates at $25^{\circ}C$ and 50% humidity with a photoperiod of 16 hours light/8 hours dark (fluence rate of $40{\mu}mol{\cdot}m^{-2}{\cdot}s^{-1}$) to examine the progress of bulb rot. After 7 days, disease levels were classified into indices 1 (no symptom) to 6 (serious bulb rot). Soil inoculation of Fol carried out with resistant or susceptible lily cultivars that had been selected through in vitro screening confirmed the reproducibility of results. Therefore, the in vitro screening method established in this study is efficient and reliable for selection of lily cultivars resistant against bulb rot disease.

• Research in Plant Disease
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• v.22 no.1
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• pp.18-24
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• 2016

This study was conducted to elucidate the cultural and pathogenic characteristics of Cladosporium cucumerinum PT1 and resistance of 81 commercial cucumbers (Cucumis sativus). Cucumber leaves and fruits appeared as scab were collected from a plastic film house located in Pyeongtaek, Gyeonggi-province, Korea in late March, 2015. A casual fungus was isolated from the diseased fruits on potato dextrose agar and it was identified as C. cucumerinum PT1 based on the morphological characteristics. To find out the effect of wounding and fruit size on the development of cucumber scab, small (<10 cm long), medium (10 to 20 cm long), and large (>20 cm long, commercially mature fruit) size cucumber fruits were harvested, C. cucumerinum PT1 pathogens were inoculated with a single droplet of suspension ($1{\times}10^5$ spores/ml) on wounded or unwounded cucumber fruits. Small fruits were completely damaged with showing severe water-soaking symptoms and fast pathogen growth regardless of wounded or unwounded. Meanwhile slight water-soaking symptoms on medium and large size fruits occurred and disease development into plant tissues was observed only on wounded fruits. Disease resistance of 81 commercial cucumber cultivars was evaluated on third-stage seedlings and small fruits by inoculating suspension ($1{\times}10^5$ spores/ml) of C. cucumerinum PT1. As a result, mini and pickling cultivar groups were resistant, 'Cheoeumcheoreom' cultivar was symptomless and the other cultivars were resistant to medium resistant. On the other hand, most of cucumber cultivars belonging to the other groups were susceptible. Disease resistance of cucumber against cucumber scab was significantly different among cultivars and a few cucumber cultivars showed different disease resistant responses to two bioassay methods using seedlings and small fruits. Therefore, to screen scab resistance in cucumber, a test using both fruits and seedlings is advisable. We think that the selected resistant cultivars can be used to control cucumber scab effectively under the farmhouse condition.

• Research in Plant Disease
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• v.11 no.2
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• pp.128-134
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• 2005

This study was conducted to elucidate effect of environmental factors on the development of white rot. In order to identify the causal agents causing white rot of Allium crops, we compared DNA profiles of a representative isolate, Sclerotium cepivorum, introduced from foreign country with Korean isolates using UP-PCR. As a result, Sclerotium isolates forming round-shaped sclerotia were identified as Sclerotium cepivorum pertaining in UP-PCR b group and Sclerotium isolates farming anamorphic-shaped sclerotia presumed to be a novel species of Sclerotium based on DNA profiles of UP-PCR. There was a big difference in DNA band pattern between two species of Sclerotium isolated in Korea. Electron micrographs of scanning electron microscope and transmission electron microscope showed morphological differences in sclerotial surface structure and rind layers between two species of Sclerotium. There were more wrinkles and pore spaces on sclerotial surface of Sclerotium sp. forming anamorphic-shaped sclerotia than that of Sclerotium cepivorum forming round-shaped sclerotia. Both of two white rot pathogens grew well at the temperature range of $10-25^{\circ}C$ with optimal temperature of $20^{\circ}C$. Sclerotia of the two pathogens were well formed at $20^{\circ}C$ and well germinated at the temperature range of $20-24^{\circ}C$, Effect of pre-incubation of sclerotia on destruction of sclerotial dormancy of two pathogens was evaluated through storing sclerotia under different temperature condition. The sclerotia of the two pathogens showed an increased capacity to germinate on potato dextroise agar when the sclerotia were incubated for 7 days at $10^{\circ}C$ after pre-treatment at $35^{\circ}C$ for 7 days. At that time, germination rate of Sclerotium sp. and 5. cepivorum was $100\%\;and\;70\%$, respectively. Flooding period and treatment temperature had an effect on sclerotial survival rate of the two pathogens. As flooding period and treatment temperature increased, sclerotial germination rate of the two pathogens decreased. It was confirmed that soil humidity played an important role on development of white rot. It was the highest disease incidence of garlic white rot when garlic were sown at potted soils infested with the two pathogens and adjusted soil humidity to $15\%$ (field moisture capacity, about -300 mb). As soil humidity increase or decrease based on $15\%$ of soil humidity, disease incidence decreased move and more.

• Research in Plant Disease
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• v.14 no.3
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• pp.187-192
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• 2008

Five environment-friendly farm materials including $Chitomate^{(R)}$, $Diegyun^{(R)}$, IC-$66D^{(R)}$, Gold $Bordo^{(R)}$, and $Biospot^{(R)}$ were examined for their growth inhibition effect of the 7 fungal pathogens of grape in vitro. $Diegyun^{(R)}$, being composed of natural ingredients which are extracted from a plant, was the most effective in suppression of mycelial growth of the fungi. $Diegyun^{(R)}$ inhibited the mycelial growth of all of fungi over 75% at $2,500{\mu}g{\cdot}mL^{-1}$ on potato dextrose agar(PDA) except Colletotrichum gloeosporioides 04-159. Growth inhibition effect of $Chitomate^{(R)}$, being composed of the chitosan, varied depending on the fungal pathogens on PDA. It inhibited the mycelial growth of the Botrytis cinerea 06-063 at the rate of 75.8% at $40,000{\mu}g{\cdot}mL^{-1}$ on PDA while it inhibited the mycelial growth of the C. gloeosporioides 04-159 at the rate of 6.5%. IC-$66D^{(R)}$ and Gold $Bordo^{(R)}$ are two different formula of the Bordeaux mixture, showed different control effects on mycelial growth inhibition. Except of Acremonium sp. the growth inhibition of IC-$66D^{(R)}$ was a little higher than Gold $Bordo^{(R)}$. $Biospot^{(R)}$, a chlorine formula, showed the strongest growth inhibition on C. gloeosporioides 04-159 among the farm materials used. Inhibition of spore germination of $Chitomate^{(R)}$, $Biospot^{(R)}$ and Gold $Bordo^{(R)}$ was higher than mycelial growth inhibition for Pseudocercospora vitis 04-152. The results suggest that the different types of environment-friendly farm materials are needed for different disease control in organic grape farm.

• The Korean Journal of Pesticide Science
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• v.4 no.3
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• pp.19-26
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• 2000

In order to select potent bioactive isolates, 70 Fusarium isolates obtained from soil and 21 plant species were screened by antifungal, insecticidal, herbicidal, and duckweed bioassays after culturing in potato dextrose broth and rice solid media. Eight (11.4%) of the 70 liquid broth cultures showed disease-controlling activities more than 80% against at least one of the 6 plant diseases tested. Fusarium sp. FO-68 isolate exhibited the most potent antifungal activity; it controlled rice blast, wheat leaf rust, and barley powdery mildew with control values more than 95%. Out of 70 solid cultures, 21 (30.0%) controlled at least one plant disease more than 80% and F. equiseti FO-68 isolate showed disease-controlling activities more than 95% against 3 plant diseases such as rice blast, tomato late blight, and wheat leaf rust. As for tile insecticidal activities, 2 liquid and 1 solid cultures showed potent insecticidal activities against pest insects more than 80%, Liquid cultures of F. oxysporum FO-61 and Fusarium sp. FO-80 isolates exhibited insecticidal activities more than 80% against green peach aphid and diamondback moth, respectively. The solid culture of Fusarium sp. FO-510 isolate had 80% insecticidal activity against green peach aphid. However, none of liquid and solid cultures of the 70 Fusarium isolates showed potent herbicidal activities against 10 upland weeds. As the results of duckweed assay, 3 liquid cultures showed 70% growth inhibitory activity at concentrations less than 1.25% of culture supernatants and 9 solid cultures had a potent inhibitory activity against duckweed growth. On the other hand, there was a significant correlation between antifungal activities and herbicidal activities against duckweed of both liquid and solid cultures of tile 70 Fusarium isolates.

• Research in Plant Disease
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• v.20 no.1
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• pp.50-53
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• 2014

Rhizopus soft rot of lily (Lilium longiflorum) caused by Rhizopus oryzae was observed in the experimental field in Taean Lily Experiment Station in Korea, 2012. The typical symptoms were water-soaked lesions on bottom stem and leaf rot. The lesion rapidly expanded and the plant was softened totally. The fungus grew vigorously at an optimum temperature ($25^{\circ}C$) and brownish colony and black sporangia were formed on potato dextrose agar medium. Sporangiophores formed on end of sporangia were sub-globose, brownish and $6-10{\mu}m$ in size. Sporangia were globose, blackish and $87-116{\mu}m$ in size. Sporangiospores were irregularly oval and sub-globose, brownish $4-8{\mu}m$ in size. On the basis of mycological characteristics, analyzing sequences of internal transcribed spacer region of ribosomal DNA, and pathogenicity test on host plants, the causal fungus was identified as R. oryzae. This is the first report of Rhizopus soft rot on lily caused by R. oryzae in Korea.

• Research in Plant Disease
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• v.9 no.2
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• pp.89-93
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• 2003

An isolate of Tobacco mosaic virus (TMV) was isolated from potato cultivar ‘Chubak’ showing vein clearing and mild mosaic at Namhae in Korea. This isolate, TMV-St, was differentiated from other tobamoviruses based on biological properties, serological relationships and nucleotide sequence analyses of coat protein genes. TMV-St caused typical symptoms on four indicator plants as compared to the tobamovirus of TMV-U1, Pepper mild mottle virus (PMMoV), and Tomato mosaic virus (ToMV), which caused economic losses in Solanaceous vegetables, tomato, pepper, and eggplant. Remarkably, the TMV-St induced distinctly different symptom of systemic chlorotic spots on Chenophodium murale. On C. murale, Gomphorena globosa, and Nic-otiana rustica, the four viruses were classed by the virulence of systemic or local infections. In serological test TMV-St antiserum showed a precipitation line with each other tabamovirus. The CP gene of TMV-St contain 477 nucleotides, and the nucleotides sequence was the most similar to that of TMV-U1.

• Research in Plant Disease
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• v.23 no.3
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• pp.234-240
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• 2017

Incidence of virus diseases in red pepper of open field in Yeongyang-Gun, Gyeongbuk Province was investigated by reverse transcription-polymerase chain reaction in 2012-2016. The infection rate of Cucumber mosaic virus (CMV), Broad bean wilt virus 2 (BBWV2), Pepper mottle virus, Potato virus Y, Pepper mild mottle virus and Tomato spotted wilt virus was 46.1%, 41.5%, 2.0%, 2.0%, 4.4% and 0.1% respectively. Incidence rate of single and mixed infection was 31.2% and 62.6%. Most of single infections were CMV and BBWV2. Among mixed infections, the incidence rate of CMV+BBWV2 mixed infection was the highest as 49.3% and most of mixed infections of triplex and tetraplex included CMV+BBWV2 mixed infection. CMV single infection caused mosaic, chlorosis, yellowing and vein necrosis and BBWV2 single infection induced cholosis and mosaic. CMV+BBWV2 mixed infection caused severe mosaic with chlorosis or malformation.