Shun-Shan Shen

In vitro and In vivo Activities of a Biocontrol Agent, Serratia plymuthica A2l-4, Against Phytophthora capsici

In vitro and in vivo activities of a biocontrol agent, Serratia plymuthica strain A2l-4, was evaluated for the control of Phytophthora blight of pepper, Strain A2l-4 inhibited mycelial growth, germination of zoosporangia and cystospores, and formation of zoospore and zoosporangia of Phytophthora capsici in vitro. In the pot experiment, incidence of Phytophthora blight of pepper in non-treated control was 100% at 14 days after inoculation, while no disease was observed in the plot treated with S. plymuthica A2l-4. In the greenhouse test, infection rate of pepper in the non-treated plots was 74.5%, while it was only 12.6％ in the plots treated with A2l-4. Results indicate that S. plymuthica A2l-4 is a potential biocontrol agent for Phytophthora blight of pepper.

Root Colonizing and Biocontrol Competency of Serratia plymuthica A21-4 against Phytophthora Blight of Pepper

The biocontrol agent Serratia plymuthica A21-4 readily colonized on the root of pepper plant and the bacterium moves to newly emerging roots continuously. The colonization of A21-4 on the pepper root was influenced by the presence ofPhytophthora capsici in the soil. When P. capsici was introduced in advance, the population density of A21-4 on the root of pepper plant was sustained more than cfu/g root until 3 weeks after transplanting. On the other hand, in the absence of P. capsici, the population density of A21-4 was reduced continuously and less than cfu/g root at 21 days after transplanting. S. plymuthica A21-4 inhibited successfully the P. capsici population in pepper root and rhizosphere soil. In the rhizosphere soil, the population density of P. capsici was not increased more than original inoculum density when A21-4 was treated, but it increased rapidly in non-treated control. Similarly, the population density of P. capsici sharply increased in the non-treated control, however the population of P. capsici in A21-4 treated plant was not increased in pepper roots. The incidence of Phytophthora blight on pepper treated with A21-4 was 12.6%, while that of non-treated pepper was 74.5% in GSNU experimental farm experiment. And in farmer`s vinyl house experiment, the incidence of the disease treated with the fungicide was 27.3%, but treatment of A21-4 resulted in only 4.7% of the disease incidence, showing above 80% disease control efficacy.

Occurrence of Blue Mold on Tomato Caused by Penicillium oxalicum in Korea

A blue mold on tomato fruit caused by Penicillium oxalicum occurred sporadically in a greenhouse at Gyeongsangnam-do Agricultural Research and Extension Services. Infection usually occurred through wounds or cracks on the fruits. Symptoms began with water soaking lesions, then became watery and softened eventually. Colony of the causal fungus was white at the early growing stage, turned green on Czapek yeast extract agar and malt extract agar. Conidia were ellipsoidal in shape and in size. Stipes were septate, smooth, thin walled, and in size. Penicilli were mostly biverticillate. Ramuli were 1-3 groups, smooth, and in size. Rami were 1-2 groups and in size. Metulae were 2-3(5) verticils, smooth, and in size. Phialides were 5-7 verticilate, ampulliform to cylindroidal, smooth, and in size. Optimum temperature for growth was about . Pathogenicity of the fungus was proved on tomato fruit according to Koch`s postulation. On the basis of mycological and pathological characteristics, the fungus was identified as P. oxalicum Currie & Thom. This is the first report of the blue mold on tomato fruit caused by P. oxalicum in Korea.

Serratia plymuthica Strain A2l-4: A Potential Biocontrol Agent Against Phytophthora Blight of Pepper

A promising biocontrol agent, A2l-4, against Phytophthora blight of pepper was selected from 351 bacterial isolates collected from rhizosphere soils and roots of onion (Allium fistulosum L.). The isolate A21-4 was identified as Serratia plymuthica based on its 16S rRNA sequence and key characteristics as compared with that of an authentic culture of S. plymuthica (ATCC No. 6109D01). The isolate readily colonized on roots of various crops including pepper when inoculated on seed and not. Strain A2l-4 showed narrow spectrum of antibiotic activity, as revealed in its strong inhibitory activity to the genera Pythium and Phytophthora, but not to Fuasrium and Rhizoctonia. In pot experiments, none of the pepper seedlings treated with A2l-4 were infected by Phytophthora capsici, while 86% of the control plants were killed by the pathogen.

Occurrence of Pink Mold Rot of Strawberry Caused by Trichothecium roseum in Korea

Strawberries rotted by pink mold rot fungus (Trichothecium roseum) were found sporadically in farm greenhouses in Sugokmyon, Jinju, Korea, from March to April in 2009 and 2010. The diseased fruits were first covered with pink-colored mold, consisting of conidia and conidiophores of the pathogen, and then became water-soaked and dark brown in color, before eventually rotting (Fig. 1A). After a pure representative specimen was isolated, we examined the mycological characteristics of the specimens in detail, using light and scanning electron microscopes. Fungal colonies were white to pinkish, and numerous conidia formed on potato dextrose agar (PDA; Fig. 1C). Conidia were ellipsoidal to pyriform, colorless, 2-celled, characteristically held together in zigzag chains, aleurioconidia 12-21×8-10 μm in size (Fig. 1D). Conidiophores were long, slender, simple, septate, bearing meristem arthrospore conidia apically, singly when young, and successively. Conidiophores were apex, 3-5 μm in size. The optimum temperature for mycelial growth was 25 oC. The measurements and taxonomic characteristics coincided with those of T. roseum (Pers.) Link ex Gray described by Gobayashi et al. (1992) and Ishikawa et al. (1998). The pure isolate of the pathogen was incubated at 25 oC, and the conidia were artificially inoculated onto strawberries. The same disease symptoms were reproduced on the fruits, and the same fungus was re-isolated from the symptoms. To identify the causal fungus, we amplified and sequenced a partial internal transcribed space (ITS) rDNA of the isolate, using the primers ITS1 and ITS4, as described by White et al. (1990). The resulting sequence of 613 bp was deposited in GenBank (accession no. HM355750). Phylogenetic analysis was conduced using MEGA4 software, with the neighbor-joining method and TajimaNei distance model. The neighbor-joining analysis (Fig. 2) showed that the ITS sequences of the isolate were similar to those of T. roseum (Seifert et al., 1997). In the phylogenetic tree (Fig. 2), the isolate was placed within a clade comprising reference isolates of T. roseum. This is the first report of pink mold rot on strawberry caused by T. roseum in Korea. Cultures of T. roseum have been deposited with the Korean Agricultural Culture Collection (KACC 45158), National Institute of Agricultural Biotechnology, Rural Development Administration, Suwon.

Effect of COY (Cooking Oil and Yolk mixture) and ACF (Air-circulation Fan) on Control of Powdery Mildew and Production of Organic Lettuce

Powdery mildew of lettuce that is a newly reported disease became a threat to organic cultivation of lettuce in Korea since the disease caused by Podosphaera fusca resulted in a half of yield loss in heavily infected fields. To improve micro-environmental conditions around lettuce, ACF (air-circulation fan) was installed on inside roof of plastic house at 6 m intervals. The ACF increased 57% of lettuce yield and reduced 71.4% of lettuce seedling death. COY (cooking oil and yolk mixture) consisted of cooking oil 0.3% and egg yolk 0.08% reduced lettuce seedling death from 89.3% to 92.9% under the greenhouse. Seven-day interval spray of COY resulted in high control values of powdery mildew of lettuce ranging from 89.6% to 96.3%, which was comparable to a fungicide, Azoxystrobin. Lettuce yield was increased about two times compared to a non-treated conventional cultivation. Qualities of lettuce such as hardness and chlorophyll content were also improved by COY and ACF combination. Effect of COY on control of the disease was improved when or 1,000 ppm was supplemented. Results indicated that the COY made of cooking oil such as canola emulsified with yolk was highly effective on control of powdery mildew of lettuce and suitable for organic agriculture, especially when combined with ACF.

Occurrence of Sclerotium Rot of Cucumber Caused by Sclerotium rolfsii

Sclerotium rot of cucumber (Cucumis sativus L.) occurred at the experimental field of Gyeongsangnam-do Agricultural Research and Extension Services in July 2012. The typical symptoms included wilt, rot, and water-soaking on stems and fruits and severely infected plants eventually died. White mycelial mats spread over lesions, and then sclerotia were formed on fruit and near soil line. The sclerotia were globoid in shape, white to brown in color and 1-3 mm in size and the hyphal width was 4-8 . The optimum temperature for mycelial growth and sclerotia formation on PDA was . The typical clamp connections were observed in the hyphae of the fungus grown on PDA. For further identification, the complete internal transcribed spacer (ITS) rDNA region was amplified and sequenced. On the basis of mycological characteristics, ITS rDNA region comparison, and pathogenicity to host plants, this fungus was identified as Sclerotium rolfsii Saccardo. This is the first report of sclerotium rot on cucumber caused by S. rolfsii in Korea.

Occurrence of Stem Rot of Wild Aster (Aster koraiensis) Caused by Sclerotium rolfsii in Korea

A destructive stem rot of wild aster (Aster koraiensis) occurred sporadically some farmers’ fields in Guman-myon, Kosonggun, Kyongsangnam-do in 2000. One of the most severely infected field in Kosong showed 28.6 percent of infection rate. The fungus also caused stem or crown rot and systemic wilt or blight of the plants. White mycelium spread over stems and petioles of infected plants and sclerotia formed on the old lesions and near the soil surface. The fungus showed maximum mycelial growth around 30°C and did not grow under 5°C and over 45°C and mycelial width were 4.3~10.2 μm. Colony was white, usually many narrow mycelial stand in the aerial mycelium and formed clamp connection. Numerous sclerotia were formed on PDA at 30°C. The shape sclerotia were globoid and 0.8~3.0 × 0.9~3.4 mm in size. The fungus was isolated repeatedly from the infected tissues and confirmed its pathogenecity to wild aster and identified as Sclerotium rolfsii. This is the first report on the stem rot of wild aster caused by S. rolfsii in Korea.

Stem Rot of Stachys sieboldii Caused by Sclerotium rolfsii in Korea

Stem rot of Stachys sieboldii occurred sporadically in the farmer`s fields at Shindeung-myeon, Sancheonggun, Gyeongnam province in Korea. The infected leaves and stems are water-soaked, rotted, wilted and finally leads to the death of the whole plants. The sclerotia, 1-3 mm, white to brown, globoid, were formed on lesions and the surface of soil line. The optimum temperature for mycelial growth and sclerotia formation was on potato dextrose agar. The typical clamp connections were observed in the hyphae of the fungus. On the basis of mycological characteristics and pathogenicity to host plants, this fungus was identified as Sclerotium rolfsii Saccardo. This is the first report of stem rot on S. sieboldii caused by S. rolfsii in Korea.

Evaluation of Hot Water Treatment for Disinfection of Vegetable Seeds for Organic Farming

Hot water treatment that is the most appropriate seed disinfection method for organic vegetable farming was evaluated in this study. Among the leafy vegetable seeds lettuce that was the most sensitive to hot water was suitable to treat at for 25 min, while Chinese cabbage and radish seeds were optimally treated at for 25 min. The treatments resulted in similar or higher seed germination rate than non-treated seeds and promoted plant growth. In addition, fungi such as Alternaria, Aspergillus, Penicillium, or Mucor grown on the seeds were suppressed over 90% and the bacterial growth on lettuce seeds reduced 98.5% by the treatment. Among the fruit vegetable seeds pumpkin that was vulnerable to hot water was suitable to treat at for 15 min, while cucumber and hot pepper seeds revealed optimum treatment at for 25 min as chinese cabbage and radish. The treatment also showed similar or higher seed germination rate and growth than non-treated seeds. Furthermore, fungi such as Rhizopus, Aspergillus, Penicillium or Mucor grown on the seeds reduced from 72.0% to 95.4%. The bacterial growth on cucumber and red pepper seeds was suppressed from 65.5% to 86.0% by the treatment. Results indicated that the hot water treatment is practical for disinfection of organic vegetable seeds and the optimum temperature and soaking time varied among the seeds.