Yong-Ki Kim

Soft Rot of Onion Bulbs Caused by Pseudomonas marginalis Under Low Temperature Storage

Soft rot occurred severely in onion bulbs stored under low temperature () in storage houses at Changyoung, Kyungnam province, Korea in early 2000. Water-soaking and yellowish-brown lesions initially appeared on the outside scales of diseased onion bulbs, gradually progressing into the inside scales. Among the bacterial isolates obtained from the lesions, K-2 isolate was found to be responsible for the disease, which grew at a temperature range of from to with optimum temperature of -. However, it showed strong pathogenicity to onion bulbs at and at 3 days and 2 months, respectively. The bacterium also caused soft rot on potato and showed hypersensitive reactions to tobacco and potato. The causal bacterium of onion soft rot was identified as Pseudomonas marginalis based on morphological, biochemical, and physiological characteristics including LOPAT, Soft rot in onion under low temperature storage caused by P. marginalis has not been previously reported.

Selection and Identification of a Hyperparasite, Ampelomyces quisqualis 94013 for Biocontrol of Cucumber Powdery Mildew

308 isolates of Ampelomyces sp. were isolated from powdery mildew fungi of 73 plant species in Korea for selection of biocontrol agents. An isolate 94013 isolated from powdery mildew fungus of red bean was selected as an effective biological control agent against cucumber powdery mildew in greenhouse. The morphological characteristics of the isolate is as follows. Pycnidia were sub-globose or elongated to pyriform, pale to dart brown, , and conidia were guttulate, straight cylindrical to fusiform, pale brown, . The isolate 94013 was identified as Ampelomyces quisqualis by morphological characteristics and rDNA ITS sequencing. The isolate A. quisqualis 94013 was different from that of the commercial product in the rDNA ITS sequence.

Assessments of Rice Yield Loss According to Infection Time of Neck Blast

Correlation between rice yield loss and infection time of neck blast after panicle emergence was analyzed in paddy fields at Icheon in 1999 and 2000. As the neck blast occurred at early heading stage, the yield loss of a early maturity variety, Jinmibyeo, ranged from 83.9% to 81.6%, while it ranged from 44.3% to 33.1% when the disease developed 30 days after heading. The regression equations of yield loss(y) caused by the neck blast infection time(x) in Jinmibyeo were y

New Hosts of Ampelomyces quisqualis Hyperparasite to Powdery Mildew in Korea

308 isolates of Ampelomyces quisqualis were isolated from powdery mildew fungi of 73 plant species in Korea from 1994 to 2004. Among them, the new mycohosts and new plant hosts of A. quisqualis were found in 13 species of powdery mildew fungi in 38 species of plant. The new hosts of A. quisqualis were Erysiphe heraclei on Heracleum moellenderfii; E. hommae on Elsholtzia splendins; E. glycines on Glycine max; E. lespedezae on Lespedeza biclor; E. pileae on Pilea mongolica; E. pisi on Phaseolus radiatus; E. polygoni on Rumex aquatica and Rumex crispus; Golovinomyce artemisiae on Artemisia princeps var. orientalis; G. cichoracearum on Rudbeckia laciniata var. hortensis; G. rubiae on Rubia akane; Oidium sp. on Valeriana fauriei, Lactuca indica var. laciniata, Carpesium triste var. manshuricum, Aster ageratoides var. turczaninow, Lufa cylindrica, Ixeris demtats Nakai, Phlox paniculata, Bidens bipinnata and Pathenocissus tricuspidata; Microsphaera alphitoides on Quercus aliema, M. pseudolonicerae on Cocculus trilobos; Podosphaera sp. on Ligustrum obtusifolium; Sphaerotheca aphanisi on Fragaria ananassa; S. balsaminae on Impatiens textori; S. fusca on Cucurbita pepo, Cucurbita maxima, Ligularia fischeri, Solanum melongena, Lagenaria leucantha, Cucumis melo var. makuwa, Acalypha australis, Cosmos bipinnatus and Aster scaber; Uncinuliella simulans on Rosa muliflora and Uncinula australiana on Lagerstroemia indica.

Biological Control of Cucumber Powdery Mildew Using A Hyperparasite, Ampelomyces quisqualis 94013

An isolate of Ampelomyces quisqualis 94013(AQ94013) was selected as an effective parasite for biological control of cucumber powdery mildew. In the greenhouse, occurrence of cucumber powdery mildew was significantly suppressed for nine days by pre-treatment with and of conidial suspension of AQ94013. The disease was effectively controlled within three to seven days by post-treatment with the suspension of AQ94013. When AQ94013 was treated at concentration of three times at seven-day interval in the vinylhouse, the control effect was higher than that treated twice at ten-day interval and that treated with fenarimol twice. As the results, Ampelomyces quisqualis 94013 could be a prospective biofungicide for biological control of powdery mildew of cucumber.

Mass Cultivation of A Hyperparasite, Ampelomyces quisqualis 94013 for Biological Control of Powdery Mildew

An isolate of Ampelomyces quisqualis 94013(AQ94013) was selected as an effective agent for biological control against cucumber powdery mildew. In order to develop mass production technique, six cereal media made with barley, rice, mille and brown rice, sorghumand rice seed were tested. Among them, barley medium was the best for the growth and conidial production of AQ94013. Optimum temperature for the mass production of AQ94013 was and followed by and . Light radiation inhibited conidial production of AQ94013 since number of conidia formed on barely medium under continuous light or 12 hrs alternative light were much less than cultured in darkness. Tthe conidia produced on the medium at maintained the parasitic ability to Sphaerotheca fusca for 30 days. A culture method of AQ94013 in barley liquid medium with adding barely power(40 g/l) in darkness for five days at using a 30 l-fermenter was very effective for mass production of conidia.

A New Method for Sclerotial Isolation of Two Species of Sclerotium from Infested Soils

White rot on Allium crops recently had a high incidence with incrensed cultivating areas of tropical garlic types in Korea. Two types of Sclerotium have known as causal agents that produce different size and shapes of sclerotia in infested fields. Therefore, we developed a new method for isolation of sclerotia from infested field soils that can be used for ecological study of Sclerotium spp. and establishment of control strategy. Soil samples collected from heavily infested fields were evenly mixed and placed on a automatic sieve shaker connected with tap water, After 10 min of shaking, residues on 0.5 mm and 0.25 mm sieves were separately collected and suspended with 70% sugar solution, which method floats sclerotia in aqueous layer, Then, floated fraction was carefully separated and mixed with a same volume of 1% sodium hypochlorite solution to differentiate with organic materials. This method provides a direct count of sclerotia under a dissecting microscopy.

Cause and Control of Lettuce Powdery Mildew Caused by Podosphaera fusca

Podosphaera fusca에 의한 상추 흰가루병은 상추 발생 병해중에서 가장 중요한 병해중 하나이다. 흰가루병 발생으로 상추재배가 피해로 인하여 재배자와 소비자를 위하여 좋은 품질의 상추를 생산하기 위한 방제법 개발이 필요하다. 상추 흰가루병 발생이 증가되는 원인은 계속적인 연중재배, 병든 식물체의 미제거, 흰가루병을 노균병으로 오인에 의한 부적절한 약제 처리 등이다. 경기도 수원시 근교에 상추 시설 재배 포장에서 미생물농약을 포함한 5가지 살균제에 대한 상추 흰가루병 방제 실험을 실시하였다. 상추 흰가루병이 발생 초기에 10일 간격 3회 분무 처리하여 최종 약제 처리 8일 후에 흰가루병 발생을 조사하였다. kresoxim-mothy SC, azoxystrobin SC, Ampelomyces quisqualis AQ94013 WP, Paenibacillus polymyxa AC-1 SC와 Bacillus Y 1336 WP를 처리한 흰가루병의 발생은 0.7%, 0.7%, 26.0%, 36.7% 각각 발생하였으며, 무처리는 55.3% 발병하였다. 상추유묘에 대하여 이들 약제의 기준량과 배량에서 약해는 없었다. 【Powdery mildew caused by Podosphaera fusca is one of the most important diseases in leafy lettuce (Lactuca sativa L.). Since the disease has been a threat to safe cultivation of leafy lettuce, its control methods have to develop to produce good quality of lettuce for farmer and consumer. Occurrence of lettuce powdery mildew is increasing more and more due to continuous cultivation of lettuce all through the year, non-removal of diseased plant parts of lettuce, spray of inadequate fungicides by mistaken acknowledge of lettuce powdery mildew for lettuce downy mildew, etc. The control effect of five fungicides against lettuce powdery mildew was examined in a plastic greenhouse located in Suwon. When fungicides were sprayed three times at 10 days-intervals in the early stage of occurrence of powdery mildew, the incidence of powdery mildew in the plants treated with kresoxim-methy SC, azoxystrobin SC, Ampelomyces quisqualis AQ94013 WP, Paenibacillus polymyxa AC-1 SC and Bacillus subtilis Y 1336 WP was 0.7%, 0.7%, 26.0%, 36.7% and 42.0%, respectively, whereas the incidence of non-treated control was 55.3% on eight days after final application. Phytotoxicity of five fungicides tested was not observed in lettuce seedling plants.】

Pathogenicity of Two Species of Sclerotium to Nine Cultivars of Garlic Cultivated Widely in Korea

Mycelial growth and days required for sclerotial formation(DRSF) in vitro, and disease incidence of infected plants in the field were investigated to evaluate disease resistance of nine garlic cultivars against two species of Sclerotium causing garlic white rot. There were differences among mycelial growth and sclerotial formation of two white rot pathogens on different garlic cultivars in vitro. Mycelial growth showed the highest level on the clove of `Daeseo`. Sclerotia of two white rot pathogen were formed the earliest on the clove of `Kodang` and the latest on the clove of `Namdo`. In field trial all of nine garlic cultivars were highly susceptible to Sclerotium cepivorum and cold-type garlics were less susceptible than warm-type garlics. Meanwhile garlic cultivars used showed differences among resistant responses to Sclerotium sp., forming large sclerotia. All of warm-type garlics showed highly susceptible response, but three cold-type garlics, `Seosan`, `Danyang` and `Yechon` showed moderate resistant response and `Euisung` showed resistant response. To evaluate cultivar resistance of garlics quantitatively disease progress curve was transformed as linear regression equation. Among the intercept (early disease incidence) and the slope (disease infection rate) obtained from the transformed equation, final disease incidence, and area under disease progress curve(AUDPC), AUDPC was the most effective to evaluate disease resistance of garlics to both of white rot pathogens. There was little correlation between mycelial growth and sclerotial formation on garlic cloves in vitro, and epidemiological parameters (early disease incidence, final disease incidence, disease infection rate, AUDPC) obtained from the field trial. Mycelial growth of S. cepivorum was positively correlated with final disease incidence and disease infection rate obtained from the field trial, meanwhile DRSF was negatively correlated with the epidemiological parameters.

Pink Root of Onion Caused by Pyrenochaeta terrestris (syn. Phoma terrestris)

Pink root of onion occurred in the fields of the Onion Experimental Station and in the main onion cultivation area in Korea in 1998 and 1999, respectively. The casual fungus of pink root was isolated only from apricot agar. Formation of pycnidia and pycnidiospores of the fungus was highest in alternating cycles of 12 hours near ultraviolet light and 12 hours in dark condition. Its morphological characteristics and pigment formation on water agar were identical with that of Pyrenochaeta terrestris. The optimum temperature for the growth of the fungus and disease development was . When onion seeds were inoculated with the spore suspension, incubated in test-tube and sown in potted soil, disease symptoms developed in onion roots 7 and 30 days after inoculation.