Hyo-Won Choi

Review of Disease Incidences of Major Crops of the South Korea in 2005

In 2004, average temperature was higher, and rainfall was less than those of previous year, The diseases of rice, barley, pepper, chinese melon, apple and oriental pear were surveyed. Seedling diseases, leaf blast, sheath blight and bacterial blight of rice, phytophthova blight, virus diseases and anthracnose of pepper, and sudden wilt syndrome and powdery mildew of chinese melon grown in plastic greenhouse were severe. Especially, sheath blight and bacterial blight of rice occurred two times higher than those of previous year, Panicle blight of rice decreased about 4 times, compared with the previous year, presumed that the lower rainy days, rainfall and RH suppressed spread of the fungal pathogens to panicles of rice. Lower rainfall during mid- and late Aug caused three-times less occurrence of phytophtora blight of red-pepper than that of the previous year, Another diseases surveyed occurred similar or less than those of the previous year.

Development of In Vitro Seedling Screening Method for Selection of Resistant Rice Against Bakanae Disease

Rice bakanae disease, caused by the fungus Fusarium fujikuroi, is one of the most important rice diseases and distributed widely in Asia. Resistance screening system in rice field had been established. However, the evaluation results of the system vary according to the environmental conditions when the test is conducted. To develop precise and rapid evaluation method of disease resistance of rice to bakanae disease, in vitro screening system was attempted in this study. The six cultivars namely, `Nampyeongbyeo`, `Junambyeo`, `Chucheongbyeo`, `Samcheonbyeo`, `Odaebyeo` and `Hwasinbyeo` were tested. They were planted onto MS agar medium (10 ml) in test tube () and incubated at and in growth chamber under 12 hr light condition. Symptoms of over growth appeared a few days after seeding and then seedling were withered 2-3 weeks after over growth. The disease symptoms such as leaf dryness on top of rice were appeared in the `Nampyeongbyeo` from 28 days at the concentration of spores/ml culturing at and then withered completely 35 days after seeding. Whereas the other varieties withered entirely 19-23 days after seeding. Using the in vitro seedling screening method, 72 rice varieties were investigated to select resistant cultivar. Finally, two resistant cultivars (`Nampyeongbyeo` and `Inwolbyeo`) and seven moderately resistant cultivars (`Hwadongbyeo`, `Seokjeongbyeo`, `Samgwangbyeo`, `Sampyeongbyeo`, `Nonghobyeo`, `Heukjinjubyeo` and, `Joanbyeo`) were selected. If in vitro seedling screening method was used for evaluation of bakanae disease resistance, it would be completed within 35 days after sowing of rice seed.

Mating Types and Optimum Culture Conditions for Sexual State Formation of Fusarium fujikuroi Isolates.

Twenty-five isolates of Fusarium fujikuroi acquired from rice seeds and rice plants evidencing symptoms of Bakanae disease were evaluated to determine their mating types and characterize the formation of their sexual state. The mating types of the isolates were evaluated via multiplex PCR with the diagnostic primers of the mating-type (MAT) region: GFmat1a, GFmat1b, GFmat2c, and GFmat2d. Among the 25 isolates, 11 were identified as MAT-1 (male), and 14 as MAT-2 (female). Four MAT-1 isolates and three MAT-2 isolates were mated and cultured to evaluate the optimal culture conditions for the production of their sexual states. Among four tested media, 10% V8 juice agar proved optimal for the perithecial production of the isolates. The isolates also generated the largest numbers of perithecia when incubated at 23°C in alternating cycles of 12 hr fluorescent light and NUV fluorescent light and 12 hr darkness.

Diversity and Pathogenicity of Fusarium Species Associated with Head Blight of Job`s Tears

율무(Coix lacryma-jobi)는 동아시아에 자생하는 작물로, 종실은 주로 건강식품이나 의약용으로 사용되고 있다. 2006년부터 2008년까지 국내 율무 재배 지역에서 이삭마름 증상이 관찰되었다. 병징은 겉껍질이 변색되고, 내부의 속씨는 마르고 쭉정이가 되는 것이다. 159개의 Fusarium균을 분리하였고, 분리 빈도별로 F. graminearum(34%), F. proliferatum(14.5%), F. verticillioides(10.1%), F. equiseti(6.9%), F. fujikuroi(6.3%) 순으로 분리되었고, 그 밖에 F. subglutinans, F. semitectum, F. poae, F. sporodochioides가 분리되었다. 분리균주의 elongation factor 1 alpha 유전자의 염기서열 분석을 통한 계통분석을 수행한 결과, NCBI GenBank에 등록된 균주와 동일한 것을 확인하였다. 분리균주의 병원성 검정을 수행한 결과, F. graminearum, F. proliferatum, F. verticillioides가 병원성이 강하였다. 이 연구는 Fusarium균에 의해 발생한 율무 이삭마름 증상에 대한 첫 번째 보고이다. 【Jobs tears (Coix lacryma-jobi) is native to East Asia, and grains of the plant are used as health food and medicinal material. Head blight symptoms of the plant were frequently observed during disease surveys in Korea from 2006 to 2008. The symptoms were characterized as discoloration of husks, and subsequently inside of mature grains were shriveled or emptied. One hundred fifty nine isolates of Fusarium species were obtained from the disease symptoms of the plant collected from several locations in the country. Out of the isolates, the most frequently isolated Fusarium species were F. graminearum (34%), F. proliferatum (14.5%), F. verticillioides (10.1%), F. equiseti (6.9%), and F. fujikuroi (6.3%). Other Fusarium species isolated were F. subglutinans, F. semitectum, F. poae, and F. sporodochioides. Elongation factor 1 alpha gene sequences of the isolates were used for phylogenetic analysis. Analyses of the sequences revealed that the isolates were confirmed to be identical with each reference species of NCBI GenBank. Pathogenicity tests showed that F. graminearum, F. proliferatum and F. verticillioides were strongly virulent to grains of Jobs tears. The present study is the first report of head blight of Jobs tears caused by Fusarium species in Korea.】

Survey of Major Disease Incidence of Rice in Korea during 1999-2008

During the period from 1999 to 2008, we surveyed the major diseases incidence of rice in Korea. Leaf blast showed 0.85% of the diseased leaf area in 2000 and then consistently decreased to 0.02% by 2008. However, panicle blast irregularly appeared by the years depending on weather conditions for disease development from heading to milk stage of rice. Diseased lesion height of sheath blight had the lowest (10.1%) incidence in 2001 and the highest (21.4%) incidence in 2007. A negative corelation (

Identification of Fusarium Species Associated with Corn Ear Rot

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Effect of Thymol and Linalool Fumigation on Postharvest Diseases of Table Grapes

In 2007, a total of 77 isolates of Fusarium spp. were obtained from ear rot symptoms of corns collected from 5 locations in Gangwon Province, Korea. The fungal isolates were identified based on their morphological features. Out of the isolates, fifteen isolates were identified as Fusarium verticillioides which formed microconidia in long chains on monophialides. Four isolates were identified as F. subglutinans which formed microconida only on false heads. Six isolates were identified as F. graminearum which produced red pigment in PDA culture. Besides these Fusarium species, F. napiform, F. nygamai, and F. oxysporum were identified from the rest isolates. To assess for genetic diversity of the isolates, a random amplified polymorphic DNA(RAPD) technique was carried out using URP primers. The results from the RAPD analysis showed that the isolates from corn were divided into 6 groups. These RAPD groups of the Fusarium species corresponded to morphological characters of the Fusarium species. The phylogenetic analysis of most isolates by DNA sequencing of EF-1 gene corresponded to morphological characters of the Fusarium species. The results of pathogenicity tests by two inoculation methods revealed that F. verticillioides, F. graminearum and F. subglutinans are strongly pathogenic to corn stalks.

Fungicide Resistance of Gibberella fujikuroi Isolates Causing Rice Bakanae Disease and Their Progeny Isolates

Abstract Several postharvest diseases of table grapes (Vitis vinifera) occur during storage, and gray mold rot is a particularly severe disease because the causal agent, Botrytis cinerea, grows at temperatures as low as 0°C. Other postharvest diseases, such as those caused by Penicillium spp. and Aspergillus spp., also often lead to deterioration in the quality of table grapes after harvest. The use of plant essential oils such as thymol and linalool, to reduce postharvest diseases in several kinds of fruits, including table grapes and oranges, has received much attention in European countries. However, to the best of our knowledge there has been no report of the use of thymol fumigation to control gray mold in table grapes in Korea. Thymol (30 μg/mL) and linalool (120 μg/mL) significantly inhibited mycelial growth and conidia germination of B. cinerea. The occurrence rate of gray mold rot of B. cinerea and other unknown fungi was significantly reduced by fumigation with 30 μg/mL thymol in several table grape cultivars, such as Campbell early, Muscat Bailey A, Sheridan, and Geobong. In this study, fumigation with 30 μg/mL thymol, had no influence on the sugar content and hardness of grapes, but reduced fungal infection significantly. This suggests that 30 μg/mL thymol could be utilized to reduce deterioration of grapes due to gray mold and other fungal infections during long-term storage.

Occurrence of Stem Canker on Rape Caused by Leptosphaeria biglobosa in Korea

A total of 25 isolates of Fusarium fujikuroi were obtained from diseased rice plants in Korea from 2006 to 2007 to assess their resistance against fungicides prochloraz and benomyl + thiram. Minimal inhibitory concentration (MIC) values of F. fujikuroi isolates were examined by agar dilution method. Most of the isolates were sensitive to the fungicides. Out of 25 isolates, six were resistant to prochloraz and three to benomyl + thiram. In addition, the isolates CF245, CF249 and CF337 showed resistant to both fungicides. The progenies ( isolates) obtained through two different crosses between sensitive parental isolates(CF202, CF232 and CF179) and resistant parental isolate (CF337) were evaluated for their mycelial growth at different temperatures and resistance against fungicides. Mycelial growth rate of isolates originated from CF202 CF232 was similar to the parental isolates. However mycelial growth rate of isolates originated from CF179 CF337 was faster than their parent isolates. In case of prochloraz, distribution ratio of sensitivity(S) to resistance(R) against to the fungicide of isolates originated from CF202 CF232 and CF179 CF337 was 86 : 14 and 78 : 22, respectively. In case of benomyl+thiram, all the isolates originated from CF202 CF232 were sensitive to the fungicide, however ratio of sensitivity(S) to resistance(R) against to the fungicide of isolates originated from CF179 CF337 was 35 : 65.

Characterization of Monilinia fructicola Associated with Brown Rot of Cherry Fruit in Korea

Stem canker symptoms were observed in a rape field in Muan, Korea during a disease survey in May 2006. A total of 15 isolates of Phoma sp. were obtained from the infected stems of the plant. All isolates were identified as Leptosphaeria biglobosa based on their morphological and cultural characteristics. The Korean isolates of L. biglobosa were assigned to `brassicae` among six subclades of L. biglobosa complex based on the entire ITS sequences of rDNA. Pathogenicity of the fungal isolates was confirmed on leaves and stems of rape by artificial inoculation. This is the first report that Leptosphaeria biglobosa causes stem canker of rape in Korea.