• Korean Journal Plant Pathology
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• v.10 no.4
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• pp.254-260
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• 1994

Magnaporthe grisea, a causal agent of blast, forms a specialized infection structure, an appressorium, to infect host. Hydrophobicity of contact surface and cAMP have been suggested as a primary environmental signal and a second messenger to trigger and mediate appressorium formation in this fungus, respectively. To generalize these factors in field isolates of M. girsea, twenty isolates originated from rice and other gramineous hosts were tested. Seventeen including rice and non-rice isolates formed appressoria on hydrophobic surface, but none of isolates formed appressoria on hydrophilic surface. Eighteen isolates formed appressoria on hydrophilic surface in the presence of IBMX, an inhibitor of phosphodiesterase, except two rice isolates. These results strongly support the hypothesis that appressorium formation by M. grisea is induced by hydrophobic hard surface and regulated by the endogenous level of cAMP in the cells. Understanding fungal development is not only of biological interest but provides new targets for novel disease control strategies.

• Research in Plant Disease
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• v.26 no.1
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• pp.38-43
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• 2020

The genome of the rice blast fungus Magnaporthe oryzae contains several types of transposable elements (TEs), and some TEs cause genetic variation that allows M. oryzae to evade host detection. We studied how five abundant TEs in rice pathogens, Pot3, Pot2, MAGGY, Line-like element (MGL) and Mg-SINE, are expressed under diverse conditions related to growth, development, and stress. Expression of Pot3 and Pot2 was activated in germinated conidia and mycelia treated with tricyclazole. Retrotransposon MAGGY was highly expressed in appressoria and tricyclazole-treated mycelia. MAGGY and Pot2 were also activated during the early and late stages of perithecia development. MGL was up-regulated in conidia and during conidial germination but not during appressorium formation. No noticeable expression of Mg-SINE was observed under most conditions. Our results should help investigate if and how condition-specific expressions of some TEs contribute to the biology and evolution of M. oryzae.

• Korean Journal of Agricultural Science
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• v.12 no.2
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• pp.206-241
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• 1985

Attempts to search infection period, infection speed in the tissue of neck blast of rice plant, location of inoculum source and effects of several conditions about the leaf sheath of rice plants for neck blast incidence have been made. 1. The most infectious period for neck blast incidence was the booting stage just before heading date, and most of necks have been infected during the booting stage and on heading date. But $Indica{\times}Japonica$ hybrid varieties had shown always high possibility for infection after booting stage. 2. Incubation period for neck blast of rice plants under natural conditions had rather a long period ranging from 10 to 22 days. Under artificial inoculation condition incubation period in the young panicle was shorter than in the old panicle. Panicles that emerged from the sheath of flag leaf had long incubation period, with a low infection rate and they also shown slow infection speed in the tissue. 3. Considering the incubation period of neck blast of rice plant, we assumed that the most effective application periods of chemicals are 5-10 days for immediate effective chemicals and 10-15 days for slow effective chemicals before heading. 4. Infiltration of conidia into the leaf sheath of rice plant carried out by saturation effect with water through the suture of the upper three leaves. The number of conidia observed in the leaf sheath during the booting stage were higher than those in the leaf sheath during other stages. Ligule had protected to infiltrate of conidia into the leaf sheath. 5. When conidia were infiltrated into the leaf sheath, the highest number of attached conidia was observed on the panicle base and panicle axis with hairs and degenerated panicle, which seemed to promote the infection of neck blast. 6. The lowest spore concentration for neck blast incidence was variable with rice varietal groups. $Indica{\times}Japonica$ hybrid varieties were infected easily compared to the Japonica type varieties, especially. The number of spores for neck blast incidence in $Indica{\times}Japonica$ hybrid varieties was less than 100 and disease index was higher also in $Indica{\times}Japonica$ hybrid than in Japonica type varieties. 7. Nitrogen content and silicate content were related with blast incidence in necks of rice plants in the different growing stage changed during growing period. Nitrogen content increased from booting stage to heading date and then decreased gradually as time passes. Silicate content increased from booting stage after heading with time. Change of these content promoted to increase neck blast infection. 8. Conidia moved to rice plant by ascending and desending dispersal and then attached on the rice plant. Conidia transfered horizontally was found very negligible. So we presumed that infection rate of neck blast was very low after emergence of panicle base from the leaf sheath. Also ascending air current by temperature difference between upper and lower side of rice plant seemed to increase the liberation of spores. 9. Conidial number of the blast fungus collected just before and after heading date was closely related with neck blast incidence. Lesions on three leaves from the top were closely related with neck blast incidence, because they had high potential for conidia formation of rice blast fungus and they were direct inoculum sources for neck blast. 10. The condition inside the leaf sheath was very favorable for the incidence of neck blast and the neck blast incidence in the leaf sheath increased as the level of fertilizer applied increased. Therefore, the infection rate of neck blast on the all panicle parts such as panicle base, panicle branches, spikelets, nodes, and internodes inside the leaf sheath didn't show differences due to varietal resistance or fertilizers applied. 11. Except for others among dominant species of fungi in the leaf sheath, only Gerlachia oryzae appeared to promote incidence of neck blast. It was assumed that days for heading of varieties were related with neck blast incidence.

• Korean Journal of Plant Resources
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• v.31 no.6
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• pp.695-703
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• 2018

Previously, we have reported a plant extract isolated from Lysimachia foenum gracum Herba as a new environment friendly biopesticide that has the mycelial growth inhibition effect on Magnaporthe oryzae, the pathogenic fungus of the rice blast disease. For the finding of additional biopesticide candidate, we tested the mycelial growth inhibitory effects about 700 species of plant extracts on PDA media. Among them, the extract of Anemarrhena asphodeloides showed prominent inhibitory effect of which $IC_{50}$ was $139.7{\mu}g/ml$. Mycelial radii of M. oryzae were measured on PDA medium containing the four organic solvent fractions isolated from total extract from A. asphodeloides. Ethyl acetate fraction showed the impressive inhibitory effect of $IC_{50}$, $54.12{\mu}g/ml$. In the subsequent rice field test for the total extract of A. asphodeloides, we obtained encouraging 62.0% control rate of rice blast disease without any phytotoxicity. It is almost equivalent to that of chemical pesticides implying the applicability of the extract as a new biopesticide. In further study, the analysis of active ingredients of the extract would be necessary for the development of a new biopesticide and for the verification of cellular mechanism by which the mycelial growth of M. oryzae inhibited.

• Proceedings of the Korean Society of Plant Pathology Conference
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• 2003.10a
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• pp.21-22
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• 2003

Fungicide treatment is the most important method for the control of plant diseases caused by phytopathogenic fungi. But fungicide resistant strains have appeared in many phytopathogenic fungi. Until now, molecular mechanisms of fungicide resistance such as mutation of target protein, overproduction of target enzyme and detoxification of fungicide have been designated. Recently, it was demonstrated that active efflux of fungicides mediated by ATP-binding cassette (ABC) transporters also contributes to fungicide resistance in several filamentous fungi, such as Aspergillus nidulans, Penicillium digitatum and Botrytis cinerea.(중략)

• Proceedings of the Korean Society of Plant Pathology Conference
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• 2000.10a
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• pp.34-34
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• 2000

• Proceedings of the Korean Society of Plant Pathology Conference
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• 1999.04a
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• pp.39.2-39
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• 1999

• Molecules and Cells
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• v.39 no.5
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• pp.426-438
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• 2016

Plant disease resistance occurs as a hypersensitive response (HR) at the site of attempted pathogen invasion. This specific event is initiated in response to recognition of pathogen-associated molecular pattern (PAMP) and subsequent PAMP-triggered immunity (PTI) and effector-triggered immunity (ETI). Both PTI and ETI mechanisms are tightly connected with reactive oxygen species (ROS) production and disease resistance that involves distinct biphasic ROS production as one of its pivotal plant immune responses. This unique oxidative burst is strongly dependent on the resistant cultivars because a monophasic ROS burst is a hallmark of the susceptible cultivars. However, the cause of the differential ROS burst remains unknown. In the study here, we revealed the plausible underlying mechanism of the differential ROS burst through functional understanding of the Magnaporthe oryzae (M. oryzae) AVR effector, AVR-Pii. We performed yeast two-hybrid (Y2H) screening using AVR-Pii as bait and isolated rice NADP-malic enzyme2 (Os-NADP-ME2) as the rice target protein. To our surprise, deletion of the rice Os-NADP-ME2 gene in a resistant rice cultivar disrupted innate immunity against the rice blast fungus. Malic enzyme activity and inhibition studies demonstrated that AVR-Pii proteins specifically inhibit in vitro NADP-ME activity. Overall, we demonstrate that rice blast fungus, M. oryzae attenuates the host ROS burst via AVR-Pii-mediated inhibition of Os-NADP-ME2, which is indispensable in ROS metabolism for the innate immunity of rice. This characterization of the regulation of the host oxidative burst will help to elucidate how the products of AVR genes function associated with virulence of the pathogen.

• Korean Journal of Agricultural Science
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• v.12 no.2
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• pp.356-369
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• 1985

In Korea, inevitable researches for the blast control exactly started from 1927 by the organization of Office of Rural Development with the local extensive outbreak of panicle blast at Jeonlla Buk-Do Province in 1926. At present, the rice blast is still one of the most destructive and widespread diseases in spite of considerable contributions by rice scientists, particularly plant pathologists during last 55 years in Korea. Rice blast control and management are very difficult because of the marked variability in pathogenicity of the blast fungus. From the results obtained through the disease surveys during last 70 years, different 3 prevalence type of blast such as bimodal leaf-blast type, bimodal panicle-blast type and bimodal continual blast type were recognized. In generally speaking, pattern of blast outbreak is said to be characterized by severe outbreak of panicle blast after slight outbreak of leaf blast with discontinuity between leaf and panicle blast. So we have to pay much attention for successful management of panicle blast giving direct influence to rice yield. Main factors induce blast epidemic were pointed out to be breakdown of the disease resistance, nutritional unbalance such as excess application of nitrogen, delay of transplantation and longspell of rain fall by extensive surveys and researches on blast during last 70 years in Korea. The fact some of Japonica varieties such as Kokuryomiyako, Tamanishiki, Ginbozu and Pungok belong to varietal group A had been cultivated with extensive acrage over 30 years in this country should be mentioned by Korean rice scientists. Differences in field resistance between varieties in the same group are detectable and apparently small but sometimes epidemiologically significant differential effects may be found out in case of blast. Much more attention should be payed to accumulate the knowledges on field resistance for successful management of blast. Excess application of nitrogen is more effective to outbreak of panicle blast than that of leaf blast of IR varieties. In comparatively low level application of nitrogen infection rate of panicle blast of IR varieties is considerably high. Low temperature effects on outbreak of blast is very great. It results in remarkable increase of the inoculum potential on the leaf lesions and infection of panicle blast in leaf sheathes of IR varieties during the booting stage. In economic point of view, it is concluded that 5 times sprays of effective fungicides including 3 times before and 2 times after heading is good enough to control blast. We have experienced no one of control measures for blast is superior to all others. The integrated control measures was established as guideline of blast control around 1950 in Korea. This guideline must be helpful for rice growers as long as rice growing continue.

• The Plant Pathology Journal
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• v.26 no.4
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• pp.386-393
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• 2010

In order to study disease resistance mechanisms in rice against the rice blast fungus Magnaporthe grisea, we screened fungal elicitor-responsive genes from rice suspension-cultured cells treated with fungal elicitors employing differential hybridization (DH). By DH screening, 31 distinct rice clones were isolated and a majority of them were full-length cDNAs encoding pathogenesisrelated (PR) genes. Sixteen of the 31 genes were upregulated at 4, 8, and 12 h following fungal elicitor treatment. To elucidate the effect of signal molecules and biotic elicitors on the regulation of rice defense genes, we further characterized the transcriptional expression patterns of representative isolated PR genes; OsGlu1, OsGlu2, OsTLP, OsRLK, and OsPR-10, following treatment with fungal elicitor, phytohormones, cycloheximide, and inhibitors of protein phosphorylation. Jasmonic acid (JA) induced transcriptional expression of OsGlu1, OsTLP, and OsRLK, but not of OsGlu2 and OsPR-10 at any of the tested time points. Salicylic acid (SA) and abscisic acid weakly induced the expression of OsTLP and OsRLK. SA showed an antagonistic effect with fungal elicitor and JA. Cycloheximide suppressed all these genes upon elicitor treatment, except for OsGlu2. Staurosporine only induced the expression of OsRLK. Application of calyculin A strongly induced OsRLK expression, but suppressed the expression of OsGlu2. Our study yielded a number of PR genes that play a role in defense mechanisms against the rice blast fungus, as well as contribute towards the elucidation of crosstalk between phytohormones and other modifications during defense signaling.