• The Plant Pathology Journal
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• v.25 no.4
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• pp.352-360
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• 2009

The potential of three plants extracts, to protect potato plants against bacterial wilt caused by Ralstonia solanacearum was determined under greenhouse and field conditions. All soil drenching treatments of aqueous plant extracts of Hibsicus sabdariffa, Punica granatum and Eucalyptus globulus significantly reduced the disease severity compared with inoculated control. Although the applications of all three plant extracts resulted in similar reductions of disease severity in field up 63.23 to 68.39%, treatment of E. globulus leaf extract was found greater in restricting the symptom development than other the two plant extracts in the greenhouse. More than 94% reduction in the bacterial wilt symptom was observed in potato plants. All tested plant extracts were effective in inhibiting the growth of bacterial pathogen, not only in vitro, but also in stem of potato plants as compared with the inoculated control Potato plants treated with extract of H. sabdariffa reduced bacterial growth more effectively than treatment with P. granatum and E. globulus. Activity of defence-related enzymes, including peroxidase, polyphenoloxidase and phenylalanine ammonia lyase, were significantly increased in plants treated with the plant extracts compared to the control during the experimental period. In general, the higher enzymes activities were determined in both inoculated and non-inoculated treated potato plants after 8 days from plant extracts treatment. These results suggested that these plant extracts may be play an important role in controlling the potato bacterial wilt disease, through they have antimicrobial activity and induction of systemic resistance in potato plants.

• Research in Plant Disease
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• v.21 no.3
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• pp.243-249
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• 2015

Soybean frogeye leaf spot caused by the fungus Cercospora sojina Hara, has known to lead a severe reduction of crop yield. Since frogeye leaf spot on soybean has recently become a serious problem in Korea, the susceptibility of recent recommended cultivars against C. sojina had been tested. To standardize the disease severity of soybean, the optimum sporulation condition of C. sojina and the disease index were established in this study. Sporulation was maximized on the 10% V8 juice agar with 12 h light and 12 h dark at $25^{\circ}C$. Spore suspension ($10^5spores/ml$) was sprayed on the leaves of soybean (V6 stage), and the disease responses to each isolate were evaluated on 28 days after inoculation. As a result, Daepung, Shinpaldal2ho, Yeonpung and Cheonga showed the resistance reaction to 8, 7, 6, 6 isolates of C. sojina, respectively, whereas Cheongja, Hwangkeum, Taekwang, Daewon, Cheonsang and Sinhwa showed the susceptible reaction to 8 isolates of C. sojina. Breeding the resistant soybean cultivars against C. sojina requires a uniform resistance for screening technique. The disease index of frogeye leaf spot on soybean developed in this study can be effectively used for the accurate field assay to select the frogeye leaf spot resistant soybean.

• The Korean Journal of Mycology
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• v.49 no.4
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• pp.555-560
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• 2021

During disease surveys conducted from 2019 to 2021 in Korea, leaf spot symptoms in rhubarb (Rheum rhabarbarum) plants were frequently observed in plants growing in fields located in Cheolwon, Taebaek, and Inje in Gangwon Province. The incidence of diseased leaves of the plants in the fields ranged from 2% to 80%. Nine single-spore isolates of Phoma sp. were obtained from lesions of the diseased leaves; all of them were identified as Didymella rhei based on their cultural, morphological, and molecular characteristics. Three isolates of D. rhei were tested for pathogenicity on rhubarb leaves using artificial inoculation. All the tested isolates caused leaf spot symptoms in the inoculated plants; the symptoms were similar to those observed in plants from the fields investigated. This is the first report of D. rhei causing leaf spot in rhubarb in Korea.

• The Korean Journal of Mycology
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• v.51 no.1
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• pp.63-68
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• 2023

From June to August 2021, we surveyed diseases affecting beet (Beta vulgaris subsp. vulgaris) plants in Cheolwon, Hoengseong, and Pyeongchang regions in Gangwon Province, Korea. We observed severe leaf spot symptoms, such as brown to dark circular or irregular spots on the leaves, in plants. Disease incidence in the plant leaves in the fields investigated at the three locations ranged from 1 to 80%. Five single-spore isolates of Phoma sp. were obtained from the diseased leaves and identified as Neocamarosporium betae based on their cultural, morphological, and molecular characteristics. Three isolates of N. betae were subsequently tested to confirm their pathogenicity in beet plants via artificial inoculation. The tested isolates caused leaf spot symptoms in the inoculated plants, similar to those observed in the plants in the investigated fields. Therefore, our findings revealed N. betae as the pathogen causing beet leaf spot in Korea.

• The Plant Pathology Journal
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• v.20 no.1
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• pp.1-6
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• 2004

The diseases caused by Xylella fastidiosa are associated with aggregation of the bacteria m xylem vessels, formation of a gummy matrix and subsequent blockage of water uptake. In the closely related pathogen, Xanthomonas campestris, xanthan gum is known to be an important virulence factor, probably contributing to bacterial adhesion, aggregation and plugging of xylem. Xanthan gum, produced by X. campestris, is an extra-cellular polysaccharide consisting of a cellulose backbone ($\bate$-1,4-linked D-glucose) with trisaccharide side chains composed of mannose, glucuronic acid and mannose attached to alternate glucose residues in the backbone. We had constructed a mutant of X. campestris lacking gumI gene that is responsible for adding the terminal mannose for producing modified xanthan gum which is similar to xanthan gum fromX. fastidiosa. The modified xanthan gum degrading endgphytic bacterium Acineto-bacter johnsonii GX123 isolated from the oleander infected with leaf scorch disease.

• International Journal of Industrial Entomology and Biomaterials
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• v.22 no.1
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• pp.11-15
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• 2011

Impact of pruning date, shoot age and weather parameters on the severity and development of grey leaf spot (Pseudocercospora mori) of mulberry was studied. The disease severity (%) increased with increase in shoot age irrespective of pruning date. Maximum disease severity was observed in plants pruned during second week of October and minimum in plants pruned during last week of December. Significant (P<0.05) influence of date of pruning, shoot age and their interaction was observed on the severity of the disease. Apparent infection rate (r) was significantly higher during plant growth period from day-48 to day-55. Average apparent rate was higher in plants pruned during first week of September and least in plants pruned during third and fourth week of December. Multiple regression analysis revealed contribution of various combinations of weather parameters on the disease severity. A linear prediction model [$Y=66.05+(-1.39)x_1+(-0.219)x_4$] with significant $R^2$ was developed for prediction of the disease under natural epiphytotic condition.

• The Plant Pathology Journal
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• v.34 no.4
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• pp.269-285
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• 2018

Bacterial leaf blight is a major disease of eucalypt, especially under nursery conditions. Different bacterial species have been associated with the disease in several countries, and despite its importance worldwide, it is not clear to date whether similar disease symptoms are caused by the same or by different etiological agents. In this study, 43 bacterial strains were isolated from blighted eucalypt leaves collected in different geographic areas of Brazil and inoculated onto a susceptible eucalypt clone. Polyphasic taxonomy, including morphological, physiological, biochemical, molecular, and pathogenicity tests showed that only certain strains of Xanthomonas axonopodis caused symptoms of the disease. Strains varied in their aggressiveness, but no correlation with geographic origin was observed. MLSA-based phylogenetic analysis using concatenated dnaK, fyuA, gyrB and rpoD gene sequences allocated the strains in a well-defined clade, corresponding to Rademarker's group RG 9.6. Inoculation of nineteen plant species belonging to seven botanical families with representative strain LPF 602 showed it to be pathogenic only on Eucalyptus spp, and Corymbia spp. Based on distinct biochemical and pathogenic characteristics that differentiate the eucalypt strains from other pathovars of the X. axonopodis species, here we propose their allocation into the new pathovar X. axonopodis pv. eucalyptorum pv. nov.

• Weed & Turfgrass Science
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• v.3 no.4
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• pp.378-381
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• 2014

A new pathogen was isolated from zoysiagrass-planted park of Jeju island in 2014. Symptoms appeared a type of irregular patches occurring brownish leaf blight, followed by stem and crown rot. The symptom was very similar to that of large patch caused by Rhizoctonia solani, a well-known devastating zoysiagrass disease. The isolate showed thin orange-colored mycelia and screlotia were formed on the medium based on cultural characteristics. The causal agent of the disease was finally identified as Waitea circinata by analysis of ribosomal DNA. On the inoculation test, Waitea circinatae showed strong pathogenicity to the zoysiagrass. The mycelia were obviously observed in the inoculated tissues. This is the first report of Waitea ring patch caused by Waitea circinata on zoysiagrass.

• Research in Plant Disease
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• v.8 no.2
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• pp.78-83
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• 2002

Tobacco diseases have not been recorded until 1900s in Korea, where tobacco plants were introduced at early 1700s. Practical researches on the disease have been conducted since mid 1960s. Major ten tobacco diseases were mosaic caused by tobacco mosaic virus·potato virus Y·cucumber mosaic virus, bacterial wilt, hollow stalk, wild fire caused by angular leaf spot strain, black shank, brown spot, powdery mildew and fusarium wilt. But their annual occurrences were varied according to changes of tobacco varieties and their cultivating practices. As no useful chemicals, several biological tactics have been developed to control the viral or bacterial diseases that give significant economic damages on sustainable crop yield, but not practicable to field farming condition yet. Transgenic tobacco plants containing foreign disease resistant genes have been developed by current bio-technology, but not released to farmers yet. Though some disease-resistant tobacco varieties have been developed by the conventional breeding technology and currently used by farmers, their disease controlling efficacy have been diminished by occurrence of the new strain or race. Future research on tobacco diseases has been focused on technical development to produce high quality tobacco with less production cost, which leads Korean tobacco industry to keep its competence against foreign industry and decreasing overall market.

• Journal of Ginseng Research
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• v.11 no.2
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• pp.91-100
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• 1987

This study was investigated and analyzed the side of phenomenological of the chlorophyll bleaching phenomenon on the leaf burning-disease of the Ginseng (Panax ginseng C.A. Meyer) leaf. Red light (660-700 nm) was confirmed as one which induced the bleaching phenomenon and blue light (400-500 nm) did not at all. Temperature as 1 environmental factor had not any influence on chlorophyll bleaching phenomenon at all. Therefore, simple burning (thermal damage) hypothesis was perfectly ruled out by the result of this study. And, low pH accelerated chlorophyll bleaching velocity. A primary factor of chlorophyll bleaching phenomenon may be peculiar structural difference of the Ginseng leaf compared with other plant.