• Research in Plant Disease
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• v.22 no.2
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• pp.72-80
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• 2016

Gummy stem blight, caused by the fungus Didymella bryoniae, is major disease of watermelons worldwide. The objective of the present study was to establish an efficient screening system to identify watermelon resistant to D. bryoniae. An GSB3 isolate was prepared from a watermelon plant showing typical symptoms of gummy stem blight in Haman-gun and identified as D. bryoniae based on molecular analysis of internal transcribed spacer sequence. A simple mass-production technique of inoculum was developed based on spore production of D. bryoniae GSB3 under several incubation conditions and their virulence on watermelon plants. Resistance degrees of 22 commercial watermelon cultivars to the GSB3 isolate were evaluated. Among them, four watermelon cultivars showing different degree of resistance response were selected for further study. Development of disease on the cultivars according to various conditions including inoculum concentrations, incubation periods in dew chamber, and incubation temperatures was investigated. From the results, we suggest an efficient screening method for resistant watermelon cultivars to gummy stem blight. Seeds of watermelon cultivar are sown and grown in a greenhouse until plant stage of 2-fully expanded leaves. Seedlings are inoculated with D. bryoniae by spraying spore suspension of the fungus at a concentration of $5.0{\times}10^5spores/ml$. The infected plants are incubated in humidity chamber at $25^{\circ}C$ for 48 hours and then transferred to a growth chamber at $25^{\circ}C$ and 80% relative humidity with 12-hour light a day. Three to four days after inoculation, disease severity of the plant are measured using percentage of infected leaf area.

• Research in Plant Disease
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• v.20 no.1
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• pp.21-24
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• 2014

Clubroot caused by the obligate biotrophic protist Plasmodiophora brassicae Woronin is one of the most damaging diseases of Brassicaceae family. In this study, we developed species-specific primer sets for rapid and accurate detection of P. brassicae. The primer sets developed amplified a specific fragment only from P. brassicae DNA while they did not amplify a band from 10 other soilborne pathogens or from Kimchi cabbage. In sensitivity test, the species-specific primer set ITS1-1/ITS1-2 could work for approximately 10 spores/ml of genomic DNA showing more sensitivity and accuracy than previous methods. With quantitative real-time PCR test, the primer set detected less spores of P. brassicae than before, confirming that the species-specific primer set could be useful for rapid and accurate detection of P. brassicae.

• Research in Plant Disease
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• v.18 no.4
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• pp.324-330
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• 2012

This study was conducted to investigate the association of race distribution of Pyricularia oryzae with rice cultivar and location. Races present in a given location were different in cultivars, and the races from a given cultivars were different by location. For precise study of race distribution, it needs to identify isolates by considering cultivation ratio and collection area. There are great differences between the resistant degree in the upland blast nursery and on the resistant degree of the leaf blast and panical blast in the paddy field. The number of virulent races in a rice cultivar was not related with the resistant degree in blast nursery or in paddy field.

• Research in Plant Disease
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• v.9 no.3
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• pp.128-130
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• 2003

Rust diseases were found on safflower (Carthamus thinctorius) fields located in Euisong-gun Gyengbuk province in Korea. The infection rate of the disease in surveyed area was about 15% in 2001. The typical symptoms of the disease appeared first as small white spots on the leaf and turn brownish, dark brown spores revealed on them. Uredospores were light brown in color, ellipsoid or spherical in shape and 21~23 ${\times}$ 21~25${\mu}m$ in size. Teliospores were chestnut-brown in color, ellipsoid or ovoid in shape and 35~40 ${\times}$ 27~33${\mu}m$ in size. Pedicels were non-color of limpidness in color and 15~30${\mu}m$ in size. The causal fungus was identified as Puccinia carthami, based on morphological charateristics. This is first report on the rust of safflower caused by Puccinia carthami in Korea.

• Research in Plant Disease
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• v.9 no.3
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• pp.149-152
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• 2003

Black leaf spot disease occurred on Dendrobium phalaenopsis grown in farmer's fields located in Bonggangmyon, Gwangyang-eup, Jeonnam, Korea. Black small spots occurred on leaves at initial stage of infection and the infected leaves turned yellow from the tip. The yellow leaves were falled, resulting in stem blighting or eventual death of the entire plant. White mycelial colony of the causal fungus grown on potato dextrose agarturned dark violet later and optimum temperature for the mycelial growth was $25^{\circ}C$. The causal fungus isolated from the black leaf spot on D. phalaenopsis was identified as Fusarium moniliforme based on the mycological characteristics and pathogenicity. The fungus also caused same symptoms on leaves of Phalaenopsis sp. and Cymbidium sp. as well sa D. phalaenopsis by wound inoculation. This is the first report on black leaf spot of D. phalaenopsis caused by F.moniliforme in Korea.

• Research in Plant Disease
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• v.9 no.3
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• pp.125-127
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• 2003

Rust disease was occurred on Iris in several farmer's fields fields located in Hoehwa-myon, Goseong-gun, Gyeong-nam province in Korea. The typical symptoms of the disease appeared first as small, yellowish spot on leaves. The spots then turn brown, their edges rised slightly, and powdery mass of yellowish brown spores revealed on the lesions. Severely infected leaves were blighted and eventually died. Urediniospores were yellowish brown to reddish brown in color, obobid to obovoid in shape and 22~30 ${\times}$ 21~25${\mu}m$m in size. Teliospores were chestnet-brown in color, oblong or clavate in shape and 32~54 ${\times}$ 12~22${\mu}m$ in size. The causal fungus was identified as Puccinia iridis, based on morphological characteristics. This is the first report on the rust of Iris nertschinskia by Puccinia iridis in Korea.

• Research in Plant Disease
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• v.8 no.3
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• pp.162-165
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• 2002

Rust disease was found on broad bean (Vuia faba) in several farmer's fields located in Changseon-myon, Nam-hae-gun, Gyeongnam province in Korea. The infection rate of the disease in the surveyed area was 84.3% in 2002. The typical symptoms of the disease appeared first as small, white spots on leaves, stems and pods. Spots, then turn brownish, their edges rised slightly, and powdery mass of yellowish brown spores revealed on them. Severely infected leaves were eventually defoliated. Uredospores were light brown in color, ellipsoid or ovoid in shape and 24~38$\times$21~26 ${\mu}{\textrm}{m}$ in size. Teliospores were dark brown in color, ellipsoid or ovoid in shape and 22~42$\times$17~27 ${\mu}{\textrm}{m}$ in size. Pedicels were sienna to luteous in color and 52~116 ${\mu}{\textrm}{m}$ in size. The causal fungus was identified as Uromyces viciae-fabae, based on morphological characteristics. This is the first report on the rust of broad bean caused by Uromyces viciae-faae in Korea.

• Research in Plant Disease
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• v.17 no.3
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• pp.386-390
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• 2011

In June 2011, walnuts (Juglans regia) from orchards in Kimcheon and Muan, in southern Korea, were found to exhibit downy mildew-like symptoms of a foliar disease. Whitish polygonal efflorescence was produced on the abaxial surface of affected leaves and discolored light green blotches on the corresponding adaxial surfaces. In the later stage of disease development, diseased tissues collapsed and became necrotic. Based on morphological and cultural characteristics, the causal fungus was identified as Microstroma juglandis. The sequence of ITS rDNA of the present isolate showed 100% similarity with those of M. juglandis obtained from GenBank databases, thus confirming its identity. Pathogenicity tests were conducted on leaves of walnut seedlings, fulfilling Koch's postulates. The disease has been previously reported in North America, Europe, Oceania and some western Asia. This is the first report of downy leaf spot on walnuts in East Asia.

• Research in Plant Disease
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• v.16 no.3
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• pp.290-293
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• 2010

Bacterial canker, caused by Clavibacter michiganensis subsp. michiganensis, is a very damaging disease to tomato (Lycopersicon esculentum) farm in Korea. It infects tomato, spreads through the xylem and causes bacterial wilt and canker. Selection of resistant cultivar is the best way to prevent or reduce the occurrence of the disease. Thirty-nine tomato cultivars, twenty-one cherry tomato cultivars and thirteen rootstock tomato cultivars were inoculated with Clavibacter michiganensis subsp. michiganensis, to evaluate tomato cultivarspecific resistance against bacterial canker. In the evaluation of 73 major commercial cultivars, 'Sunmyung', 'Sweet', 'Akiko', 'Dadaki', 'Match', 'Magnet', 'Friend', and 'Greenpower' were found to have a high level of resistance to bacterial canker of tomatoes.

• Research in Plant Disease
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• v.16 no.3
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• pp.294-298
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• 2010

Thirty-two tomato cultivars, eleven cherry tomato cultivars and eight rootstock tomato cultivars were inoculated with Meloidogyne incognita, to evaluate tomato cultivars for resistance against root-knot nematodes. One tomato cultivar, Homerunking was proved to be resistant while eight cultivars such as Regendsummer, Regend, Sunmyung, Pinktop, Top3, Delice, Tasha and Lilyance were moderately resistant to the 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 eight rootstock tomato cultivars, two cultivars (Bukinghagae, Special) were resistant and five cultivars (B-blocking, Solution, Dongbanja and Greenpower) were moderate.