• Korean Journal Plant Pathology
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• v.14 no.6
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• pp.618-621
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• 1998

In pseudoperonospora humuli, the cause of hop downy mildew, environmental and host factors affecting laboratory production of oospore were examined. After 7 days incubation of leaf disk inoculated with sporangia on water, additional incubations were carried out under different conditions of temperature and moisture. Oospore production was also compared between very susceptible (Nugget) and resistant (Fuggle) hop cultivars. Oospores were not produced at 18$^{\circ}C$ regardless of other incubation conditions. Leaf disks failed to produce oospore when incubated on water for up to 18 days at 8$^{\circ}C$. No oospores formed on infection sites without necrosis. However, abundant oospores were produced at necrotized infection sites when inoculated leaf disk incubated on dry filter paper for 5 days at 8$^{\circ}C$. Both susceptible and resistant hop cultivars produced abundant oospores. In the measurement of optimal temperature for oospore production, oospores were produced at 6 to 12$^{\circ}C$ Most abundant oospores were produced at 8$^{\circ}C$. We suggest that proper combination of low temperature, dryness and necrosis may be a critical environmental factors for oospore production of P. humuli.

• The Korean Journal of Mycology
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• v.37 no.1
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• pp.114-116
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• 2009

In this study, we selected suitable broth media for mass production of Phytophthora capsici oospore, investigated oospore germination and secured $F_1$ progeny. Carrot broth and V8C broth were determined most effective for oospore formation by calculating and comparing oospore concentration produced from 8 different liquid media. Eleven strains were selected from P. capsici (CapA)/P. tropicalis (CapB) and 9 crosses were formed. Oospore progeny were produced, isolated and germinated from A1 and A2 combinations of P. capsici (CapA) with P tropicalis (CapB). This resulted in a total number of 129 $F_1$ isolates of P. capsici/P. tropicalis with a 0.64-4.0% (mean 1.85%) oospore germination.

• The Korean Journal of Mycology
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• v.18 no.4
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• pp.203-208
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• 1990

Sexual reproductive structure of Phytophthora capsici in vitro was round shape with thick wall and $24.4\;{\mu}m$ of diameter ranging $20-32.5\;{\mu}m$. Oogonium was $26.7\;{\mu}m$ $(21-37.5\;{\mu}m$) and $6.5-{\times}5.4m$ $(6-8{\times}5-6{\mu}m)$ for antheridium as doughnut shaped. Since mycelial contact of the paired cultures initiated right after inoculation, mycelial expansion phase was followed. Oospore morphogensis could be divided into the four phases for reproducing adult oospores. The optimum temperature for oospore reproduction was $20-24^{\circ}C$, whereas a retard trend for oospore formation was at the temperature above $25^{\circ}C$. Korean squash agar medium showed a higher oospore formation than the existing V-8 agar medium. Red pepper fruit agar medium was next. No oospore was reproduced on the red pepper leaf medium. Diurnal light with $1800{\pm}300$ and $800{\pm}300$ Lux showed rather retardation for oospore formation than dark conditions.

• The Korean Journal of Mycology
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• v.22 no.4
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• pp.281-285
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• 1994

Zoospore progenies of Phytophthora cactorum were relatively uniform and similar to their respective parent in the rate of linear extension, whereas oospore progenies were greatly various. Also, the character of colony pattern was quantitatively various in oospore progenies but not zoospore progenies. Therefore, these results suggested that multiple genes were involved in determining growth rate and colony morphology of P. cactorum, and support the hypothesis that species of Phytophthora are diploid during the vegetative phase.

• Korean Journal of Plant Resources
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• v.14 no.1
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• pp.8-14
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• 2001

The effects of media, cholesterol, $\beta$-sitosterol and lecithin on the growth and oospore production of the isolates KM10, U6, CDB6, MHB6, JD1 (A$^2$type) of Phytophthora infestans isolated in Korea and F8l7, DNC303 (A$^1$type), IB908, DN107 (A$^2$type) obtained from Japan were investigated. Mycelium of P. infestans grew better on V-8 juice agar and rye meal agar than on the other media. Oospores were produced most abundantly on V-8 juice agar. Mycelium extended more 16.6, 8.3, and 5.2% on V-8 juice agar supplemented with 5 $\mu\textrm{g}$/$m\ell$ of cholesterol, $\beta$-sitosterol and lecithin, respectively, and oospores are produced 76.0, 58.0, and 34.6 % on V-8juice agar supplemented with 5 $\mu\textrm{g}$/$m\ell$ of cholesterol, $\beta$-sitosterol and lecithin, respectively. Oospores more produced on detached potato plant disks when $A^1$ and $A^2$ type exist simultaneously which indicating that variation of population can occur in the field, but the rate of oospore formation and the number of oospores produced was low and small quantity.

• The Korean Journal of Pesticide Science
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• v.13 no.4
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• pp.283-289
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• 2009

Isolation frequency of resistant isolates of Phytophthora capsici to metalaxyl was reported to be 38.9% through the resistance monitoring for metalaxyl in P. capsici causing pepper Phytophthora blight. Metalaxyl was very effective to mycelium growth, while not to zoosporangium germination and zoospore release. $EC_{50}$ values of metalaxyl in the inhibition of mycelium growth were 0.204, 0.151, 0.379, and $0.215\;{\mu}g\;mL^{-1}$ against each isolate sensitive to the fungicide as P. capsici 06-119, 06-143, P08-7, and P08-31, respectively, whilst those were 5.242, 5.724, 6.621, and $5.377\;{\mu}g\;mL^{-1}$ in P. capsici 06-125, 06-155, P08-50, and P08-60. For the field fitness, several factors, which were mycelium growth, zoosporangium germination, zoospore release, virulence to pepper plants, and the zoosporangium and the oospore production, were investigated with 4 sensitive isolates and 4 resistant isolates. Between 2 groups differentiated by the sensitivity of metalaxyl, there was no significance in mycelium growth, zoosporangium germination, zoospore release, and virulence to pepper plants. However, the zoosporangium and the oospore production in each resistant isolate, which were related to survival of P. capsici in fields, were superior to those of sensitive isolates. Based on results of this study, it was suggested that the increase of the percentage of resistant isolates to metalaxyl resulted from the high capacities of the zoosporangium and the oospore production.

• The Plant Pathology Journal
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• v.25 no.2
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• pp.121-127
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• 2009

Since July 2005, survey of chestnut ink disease was carried out in chestnut stands located at southern parts of Korea. Dead chestnut trees showing inky ooze on necrotic trunks were found in two different locations. In order to isolate and identify the causal fungus, infected tissues and soil samples around dead or dying trees were collected and placed on Phytophthora-selective medium. Rhododendron and chestnut tree leaves were used as a bait to isolate the fungus from soil samples by attracting zoospores in soil suspensions. On V-8 culture medium, the isolates produced homothallic oogonia with protuberances ($34.0-46.2{\times}21.9-26.7{\mu}m$) abundantly, but did not produced sporangia. Mass production of sporangia was possible by immersing agar plugs with actively growing mycelium in the creek water at $18^{\circ}C$ for 3 days. Sporangia were papillate, and ovoid to obpyriform ($17.0-38.9{\times}14.6-29.2{\mu}m$) in shape. Comparison of the ITS sequences revealed that the isolates had 100% identity to the P. katsurae isolates from Japan and New Zealand and 99.6% identity to other P. katsurae isolates. All of the examined isolates from Korea were completely identical to each other in ITS sequence. Numerous sporangia were formed in filtered as well as unfiltered creek water, but no sporangia formed in sterilized distilled water. Light induced sporangia formation, but has no influence on oospore formation. Amendments of ${\beta}$-sitosterol in culture media have no significant effect on mycelial growth but significantly stimulate oospore and sporangia formation.

• The Korean Journal of Mycology
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• v.44 no.2
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• pp.73-81
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• 2016

The Albuginales (Oomycetes) consist of obligate biotrophic pathogens, none of which is culturable on artificial media. This group causes white blister rust disease in diverse angiosperm plants, including many economically important crops such as sunflower, horseradish, rape, radish, spinach, and wasabi. Recent advances in molecular phylogenetic tools and findings of new morphological characters have advanced our knowledge on their diversity, evolution, and systematics. This review introduces the white blister rusts and discusses recent innovations resulting from studies on Albuginales.

• Mycobiology
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• v.47 no.3
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• pp.273-279
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• 2019

A new species, Pythium subutonaiense, isolated from aquatic environments (lake) in China is being described based on morphological characters and molecular evidence. The isolates grew at temperatures between $5^{\circ}C$ and $38^{\circ}C$, and the optimum temperature was $30^{\circ}C$, with a radial growth rate of 17.6 mm at $25^{\circ}C$ per day. It is homothallic and characterized by globose to sub-globose shaped and mostly terminal or sometimes catenulate hyphal swellings, filamentous non-inflated sporangia, and smooth oogonia with hypogynous and monoclinous antheridia that contained one plerotic oospore. In phylogenetic analysis, inferred based on the internal transcribed spacer region of the ribosomal RNA gene and mitochondrial cytochrome c oxidase subunit 1 gene, the new species formed a distinct lineage in Pythium clade B. Differences between the new species and phylogenetically related and morphologically similar species are discussed.

• The Plant Pathology Journal
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• v.22 no.1
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• pp.28-35
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• 2006

Virulence and genetic diversity were studied using 21 isolates of Sclerospora graminicola, the pearl millet downy mildew pathogen collected from major pearl millet growing areas of India. Variability for virulence was determined by inoculating a set of 10 differential hosts with the S. graminicola isolates in a greenhouse. The isolates varied for latent period (6.4 to 11 days), disease incidence (0 to $98\%$), virulence index (0 to 18.7) and oospore-production potential (1 to 4). Among the 21 isolates, Sg 139 (Rajasthan) was the most virulent and Sg 110 (Tamil Nadu) the least virulent. Based on virulence index (disease incidence$\time$slatent $period^{-1}$), the 21 isolates were classified into eight virulence groups. Genetic diversity among isolates was studied using AFLP markers. Based on similarity index of banding pattern, the 21 isolates were clustered into eight genotypic groups. The AFLP groupings, however, did not match with that of the virulence groupings, and these two were found independent. The isolate Sg 139 that remained distinct in both pathogenic and genetic groupings indicated its highly virulent nature. Implications of these results in downy mildew resistance breeding are discussed.