• The Plant Pathology Journal
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• v.32 no.1
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• pp.16-24
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• 2016

In this study, antifungal activity of essential oils of Cymbopogon citratus and Ocimum basilicum and two fungicides Mancozeb and Metalaxyl-Mancozeb in six different concentrations were investigated for controlling three species of Phytophthora, including P. capsici, P. drechsleri and P. melonis on pepper, cucumber and melon under in vitro and greenhouse conditions, respectively. Under the in vitro condition, the median effective concen- tration ($EC_{50}$) values (ppm) of plant essential oils and fungicides were measured. In greenhouse, soil infested with Phytophthora species was treated by adding 50 ml of essential oils and fungicides (100 ppm). Disease severity was determined after 28 days. Among two tested plant essential oils, C. citratus had the lowest $EC_{50}$ values for inhibition of the mycelial growth of P. capsici (31.473), P. melonis (33.097) and P. drechsleri (69.112), respectively. The mean $EC_{50}$ values for Metalaxyl-Mancozeb on these pathogens were 20.87, 20.06 and 17.70, respectively. Chemical analysis of plant essential oils by GC-MS showed that, among 42 compounds identified from C. citratus, two compounds ${\beta}$-geranial (${\alpha}$-citral) (39.16%) and z-citral (30.95%) were the most abundant. Under the greenhouse condition, Metalaxyl-Mancozeb caused the greatest reduction in disease severity, 84.2%, 86.8% and 92.1% on melon, cucumber, and pepper, respectively. The C. citratus essential oil reduced disease severity from 47.4% to 60.5% compared to the untreated control ($p{\leq}0.05$). Essential oils of O. basilicum had the lowest effects on the pathogens under in vitro and greenhouse conditions. These results show that essential oils may contribute to the development of new antifungal agents to protect the crops from Phytophthora diseases.

• The Korean Journal of Mycology
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• v.27 no.6 s.93
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• pp.394-398
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• 1999

Taxonomic and genetic analysis of Phytophthora species belonging to six different morphological groups (GI, GII, GIII, GIV, GV, GVI) was conducted using RAPD method. Amplified fragments ranged $0.3{\sim}3.2$ kb in their molecular weights. Among total of 145 bands, there were 109 polymorphic bands. Seven isolates of P. infestans showed high similarities of $0.92{\sim}0.99$, and P. infestans isolate 3 from potato showed similarities of $0.93{\sim}0.95$ compared with other P. infestans. Among isolates of P. capsici, similarities of $0.77{\sim}0.86$ were observed and they were grouped in 80% level. P. cinnamomi and P. cryptogea isolates which belonging to group GVI showed very similar RAPD fingerprinting pattern. Primers OPA-04, OPA-17, OPA-18, OPA-19, and OPB-12 showed high level of differences among the tested isolates in major bands and molecular weights. The similarity between the isolates was 0.67. P. megasperma and P. sojae in group GV showed similarity of 0.65. These two isolates showed big differences in single major band in reactions with primers OPA-08, OPA-17, and OPA-19. Phytophthora-specific and P. infestans-specific molecular markers were also selected with one of the random primers tested. In reaction with primer OPA-20, all the genus Phytophthora showed common band at 600 bp, and all the P. infestans isolates showed specific band at 680 bp. These markers can be useful for identification of Phytophthora speices or P. infestans. As a result, P. infestans isolated from tomato and/or potato can easily be differentiated from other Phytophthora species with this primer.

• Korean Journal of Soil Science and Fertilizer
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• v.51 no.1
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• pp.28-34
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• 2018

Yuzu (Citrus junos) gummosis disease, caused by Phytophthora nicotianae, was first reported in 1997. As known in citrus, Phytophthora is the most fastidious soil-borne pathogen to control. In order to minimize its damage to Citrus spp., integrated pest management (IPM) approach, including fungicide chemicals and resistant cultivars, is necessary. Therefore, in this study we tried to evaluate tolerance of yuzu cultivars and its related species against yuzu Phytophthora. Trifoliate orange was evaluated as a susceptible host to yuzu Phytophthora by both mycelial growth onto extract media and immature fruit inoculation. However, in zoospores spray-inoculation on 2-year-old cuttings tree, trifoliate orange appeared to have a resistant property as showing less than 6% diseased leaf rate. Among yuzu cultivars only 'Namhae No. 1' appeared resistant property against both P. nicotianae and P. citrophthora. The 'Namhae No. 1' showed 5.7% and 10.6% diseased leaf ratio by P. nicotianae and P. citrophthora, respectively. Clearly, in order to reduce damages caused by two yuzu Phytophthora, we suggest that growers may utilize a trifoliate orange as a rootstock and 'Namhae No. 1' as a scion for fruit production.

• Mycobiology
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• v.43 no.3
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• pp.288-296
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• 2015

Thailand is one of the largest citrus producers in Southeast Asia. Pathogenic infection by Phytophthora, however, has become one of major impediments to production. This study identified a pathogenic oomycete isolated from rotted roots of pomelo (Citrus maxima) in Thailand as Phytophthora nicotianae by the internal transcribed spacer ribosomal DNA sequence analysis. Then, we examined the in vitro and in vivo effects of Chaetomium globosum, Chaetomium lucknowense, Chaetomium cupreum and their crude extracts as biological control agents in controlling this P. nicotianae strain. Represent as antagonists in biculture test, the tested Chaetomium species inhibited mycelial growth by 50~56% and parasitized the hyphae, resulting in degradation of P. nicotianae mycelia after 30 days. The crude extracts of these Chaetomium species exhibited antifungal activities against mycelial growth of P. nicotianae, with effective doses of $2.6{\sim}101.4{\mu}g/mL$. Under greenhouse conditions, application of spores and methanol extracts of these Chaetomium species to pomelo seedlings inoculated with P. nicotianae reduced root rot by 66~71% and increased plant weight by 72~85% compared to that in the control. The method of application of antagonistic spores to control the disease was simple and economical, and it may thus be applicable for large-scale, highly effective biological control of this pathogen.

• The Plant Pathology Journal
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• v.17 no.3
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• pp.154-158
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• 2001

A severe root rot of kiwifruit caused by a species of Phytophthora occurred in 1-to 5-year-old vines at the south coast region of Korea in 1997. Infected vines exhibited leaf chlorosis, scorch and defoliation, root and stem rot, and eventual death. The disease was relatively severe in poorly drained lowlands, of which 19 out of 23 fields were damaged by the disease. Meanwhile, only one among 58 upland fields was infected by the disease. Incidence of infected vines reached over 80% in heavily damaged fields and a species of Phytophthora was isolated from inner tissues of roots, stems, and rhizosphere soils of the plants. The causal pathogen was identified as P. drechsleri based on its mycological characteristics. Pathogenicity of the fungus was confirmed by artificial inoculation to seedlings of kiwifruit 'Hayward'. The pathogen was re-isolated from the inoculated plants showing symptoms similar to those observed in the fields. Root rot of kiwifruit caused by P. drechsleri has not been reported previously in Korea.

• The Plant Pathology Journal
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• v.16 no.1
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• pp.29-35
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• 2000

The internal transcribed spacer regions (ITS I, 5.8S and ITS II) of the ribosomal DNAs were amplified from Korean isolates of Phytophthora spp. and sequenced to characterize them. Sequences from 33 isolates previously identified as P. boehmeriae, P. cactprum, P. cambivora, P. capsici, P. cinnamomi, P. erythroseptica, P. infestans, P. megasperma, P. melonis, P. nicotianae, P. palmivora and P. sojae were compared with published sequences, and a phylogenetic tree was produced. All isolates belonging to 10 species, P. cactorum, P. cambivora, P. capsici, P. cinnamomi P. citricola, P. infestans, P. nicotianae, P. palmivora and P. sojae were clearly clustered into published isolates of each species above 97% bootstrap value. Cucurbits isolates of Phytophthora previously identified as either P. melonis or P. drechsleri showed distinct evolutionary lineages from the P. megasperma was closely related to isolates of P. cryptogea-P. drechsleri showed distinct evolutionary lineages from the P. cryptogea-P. drechsleri complex group, indicating that P. melonis is a valid species. A Korean isolate of P. megasperma was closely related to isolates of P. erythroseptica showed distant genetic relationship with published isolates of P. erythroseptica (CBS 956.87). It is probable that the two Korean isolates could be genetically different from foreign isolates or misidentified. A grouping of species according to ITS sequence divergence matched, to some degree, the broad classification based on type of papilla. However, a separation of semi-papillate species and papillate species was not wvident in this study.

• Proceedings of the Korean Society of Plant Pathology Conference
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• 2003.10a
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• pp.128.3-129
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• 2003

A leaf blight disease caused by a species of Phytophthora has been observed on castor bean plants growing near dwelling houses in Manchon-dong, Daegu since 1993. The first isolate that we have kept was producing papillate, ovoid-obpyriform to obpyriform sporangia with on a simple sympodial sporangiophore from diseased tissue placed on water agar plates. The pure isolate, however, did not sporulate on agar media, and rarely even in water, but produced mycelial swellings and chlamydospores in water. Sporangia measured 26.1-77.4 ${\times}$ 23.2-44.0$\mu\textrm{m}$. Chlamydospores were either terminal or intercalary, and measured 24-29.4$\mu\textrm{m}$ in diameter. Sex organs were not formed in a single culture. In 2003, another pure isolate was isolated from castor bean plants with similar symptoms at the same place. The second isolate was distinct from the first one in that the second isolate was readily and abundantly sporulating on V8 juice agar plates. Sporangia of the second isolate were papillate, ovoid and caduceus with a pedicel. Sporangia measured 19.5-48.8 x 17.6-34.3$\mu\textrm{m}$ with 3.7$\mu\textrm{m}$ high papilla and 4.1$\mu\textrm{m}$ long pedicel. No sex organs were formed in a single isolate culture. Both isolates were pathogenic on castor bean plants. Results of the efforts to identify the two species of Phytophthora will be discussed.

• Journal of Environmental Science International
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• v.23 no.9
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• pp.1601-1608
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• 2014

Plasma reactor was used for the inactivation of Phytophthora capsici which is phytophthora blight pathogen in aquiculture. Effects of first voltage, second voltage, air flow rate, pH, incubation water concentration were examined. At the low $1^{st}$ voltage, under 80 V, the lag phase was noticed within 30 sec, however, it was not shown over 100 V. The variation of optimum operation condition was not shown by the variation of microorganisms. However, the inactivation rate was different by the variation of species of microorganisms. The inactivation rate and efficiency were increased by the increase of $2^{nd}$ voltage. The highest initial inactivation rate was shown at pH 3 and the rate was decreased by the increase of pH. The inactivation rate increased by the increase of air flow rate, however, it was shown as similar at the rate of 4 L/min and 5 L/min. The inactivation rate was distinctly decreased at the three times concentration of incubation solution comparing at the distilled water and basic incubation solution.

• Mycobiology
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• v.43 no.1
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• pp.63-70
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• 2015

Phytophthora diseases have become a major impediment in the citrus production in Thailand. In this study, an isolate of Phytophthora denominated as PHY02 was proven to be causal pathogen of root rot of Pomelo (Citrus maxima) in Thailand. The isolate PHY02 was morphologically characterized and identified as Phytophthora palmivora based on molecular analysis of an internal transcribed spacer rDNA sequence. This work also presents in vitro evaluations of the capacities of Chaetomium spp. to control the P. palmivora PHY02. As antagonists, Chaetomium globosum CG05, Chaetomium cupreum CC3003, Chaetomium lucknowense CL01 inhibited 50~61% mycelial growth, degraded mycelia and reduced 92~99% sporangial production of P. palmivora PHY02 in bi-culture test after 30 days. Fungal metabolites from Chaetomium spp. were tested against PHY02. Results showed that, methanol extract of C. globosum CG05 expressed strongest inhibitory effects on mycelial growth and sporangium formation of P. palmivora PHY02 with effective dose ED50 values of $26.5{\mu}g/mL$ and $2.3{\mu}g/mL$, respectively. It is interesting that C. lucknowense is reported for the first time as an effective antagonist against a species of Phytophthora.

• Research in Plant Disease
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• v.12 no.3
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• pp.272-277
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• 2006

Recycled irrigation water is a primary inoculum source of Phytophthora spp. and is capable of spreading propagules throughout nursery cultivation. Ozonation is commonly used to disinfest the recycled irrigation water; however, ozone has not been fully researched as a disinfectant for this purpose. In this study, zoospores of four species of Phytophthora were exposed for $1{\sim}9$ min to free available ozone at $0.1{\sim}0.3,\;0.5{\sim}0.7,\;0.9{\sim}1.2,\;1.4{\sim}1.7\;and\;1.9{\sim}2.2mg/l$. Zoospores, mycelial fragments, and culture plugs of P. nicotianae also were exposed to ozone concentrations ranging from 0.1 to 2.2 mg/l for periods ranging from 1 to 9 min. In addition, ozonated water was assayed monthly in 2004 and 2005 at two commercial nurseries, and quarterly in the first year at two other nurseries in Suwon, for ozone and survival of pythiaceous species using a selective medium. No zoospores of any species tested survived endpoint free ozone at 1.4 mg/l while limited mycelial fragments of P. nicotianae survived at 1.9 mg/l, and mycelial plugs treated at the same level of ozone were able to produce few sporangia. Phytophthora spp. were recovered only from nursery irrigation water with levels of free ozone at 0.3 mg/l or lower. The results of this study are essential for improving current ozonation sterilization.