Myeong Hyeon Nam

Biocontrol Activity of Acremonium strictum BCP Against Botrytis Diseases

Biological control activity of Acremonium strictum BCP, a mycoparasite on Botrytis cinerea, was examined against six plant diseases such as rice blast, rice sheath blight, cucumber gray mold, tomato late blight, wheat leaf rust, and barley powdery mildew in growth chambers. The spore suspension of strain BCP showed strong control activities against five plant diseases except against wheat leaf rust. On the other hand, the culture filtrate of A. strictum BCP was effective in controlling only cucumber gray mold and barley powdery mildew. Further in vivo biocontrol activities of A. strictum BCP against tomato gray mold were investigated under greenhouse conditions. Control efficacy of the fungus on tomato gray mold increased in a concentration-dependent manner. Treatment of more than spores/ml significantly controlled the disease both in tomato seedlings and in adult plants. The high disease control activity was obtained from protective application of the strain BCP, whereas the curative application did not control the disease. Foliar infections of B. cinerea were controlled with spores/ml of A. strictum BCP applied up to 7 days before inoculation. In a commercial greenhouse, application of A. strictum BCP exhibited the similar control efficacy with fungicide procymidone (recommended rate, ) against strawberry gray mold. These results indicate that A. strictum BCP could be developed as a biofungicide for Botrytis diseases under greenhouse conditions.

Taxonomic Re-evaluation of Colletotrichum gloeosporioides Isolated from Strawberry in Korea

For the past two decades, the causal agent of anthracnose occurring on strawberry in Korea was considered Colletotrichum gloeosporioides. However, the recent molecular analysis has shown that the genus Colletotrichum has undergone many taxonomic changes with introduction of several new species. As a result, it revealed that C. gloeosporioides indeed consisted of more than 20 distinct species. Therefore, the Korean pathogen isolated from strawberry should be reclassified. The shape and size of the conidia of the pathogen were not distinctly different from those of C. gloeosporioides and C. fructicola, but it differed in shape of the appressoria. A combined sequence analysis of partial actin, glycer-aldehydes-3-phosphate dehydrogenase genes, and the internal transcribed spacer regions showed that the strawberry isolates formed a monophyletic group with authentic strains of C. fructicola. On the basis of these results, the anthracnose fungi of the domestic strawberry in Korea were identified as C. fructicola and distinguished from C. gloeosporioides.

Control Efficacy of Milk Concentration Against Powdery Mildew of Strawberry

The aim of this study was to determine the effect of milk as one of the environmental friendly materials that substitute chemical fungicides for control powdery mildew (Sphaerotheca aphanis) of strawberries (Fragaria × ananassa Duch.). ``Maehyang`` and ``Akihime`` varieties planted in greenhouses were evaluated for the control of powdery mildew. Applications of 5%, 10% and 20% milk had much better effects on controlling powdery mildew. In particular, 10% milk showed a higher efficacy than other concentrations applied onto strawberry in greenhouse experiments. Foliar spray application of 10% milk was effective for powdery mildew,whereas drench application was not. Also, foliar spray of 10% milk was able to accelerate more firmness and calcium contents of strawberry fruits than the nontreated.The 10% milk applied with fertilizer salts (Ca(H2PO4)2·H2O and KH2PO4) showed there was a similar efficacy to 10% milk alone in greenhouse experiments. White crystals and cracks on strawberry fruits appeared by 20% milk. This result indicated that 10% milk was a useful substitute for fungicides to control powdery mildew of strawberry.

Cladosporium cladosporioides and C. tenuissimum Cause Blossom Blight in Strawberry in Korea

Abstract Blossom blight in strawberry was first observed in a green house in Nonsan, Damyang, and Geochang areas of Korea, between early January to April of 2012. Disease symptoms started as a grey fungus formed on the stigma, which led to the blossom blight and eventually to black rot and necrosis of the entire flower. We isolated the fungi purely from the infected pistils and maintained them on potato dextrose agar (PDA) slants. To test Koch’s postulates, we inoculated the fungi and found that all of the isolates caused disease symptoms in the flower of strawberry cultivars (Seolhyang, Maehyang, and Kumhyang). The isolates on PDA had a velvet-like appearance, and their color ranged between olivaceous-brown and smoky-grey to olive and almost black. The intercalary conidia of the isolates were elliptical to limoniform, with sizes ranging from 5.0~10.5 × 2.5~3.0 μm to 4.0~7.5 × 2.0~3.0 μm, respectively. The secondary ramoconidia of these isolates were 0- or 1-septate, with sizes ranging betweem 10.0~15.0 × 2.5~3.7 μm and 8.7~11.2 × 2.5~3.2 μm, respectively. A combined sequence analysis of the internal transcribed spacer regions, partial actin (ACT), and translation elongation factor 1-alpha (TEF) genes revealed that the strawberry isolates belonged to two groups of authentic strains, Cladosporium cladosporioides and C. tenuissimum. Based on these results, we identified the pathogens causing blossom blight in strawberries in Korea as being C. cladosporioides and C. tenuissimum.

Fungicide Spray Program to Reduce Application in Anthracnose of Strawberry

The effect of various fungicides on anthracnose of strawberry, caused by Colletotrichum gloeosporioides, was determined in vitro, and in greenhouse and field trials. The values of benomyl were clearly different between two sensitive and resistant groups of isolates. Iminoctadine tris had lower values than mancozeb and propineb as protective fungicides and the response of mancozeb, propineb and azoxystrobin was variable depending on the isolate. In the greenhouse, pre- and post- inoculation fungicide applications significantly reduced disease compared to the non-treated control. Propineb, mancozeb and azoxystrobin were effective in controlling the disease when applied prior to inoculation. Metconazole and prochloraz-Mn treatments as ergosterol biosynthesis-inhibiting fungicides had the lowest incidence of anthracnose. In the nursery field trials in 2009 and 2010, the reduced fungicide spray program provided similar levels of disease control compared to the calendar-based applications with captan. A reduced spray program based on efficacious fungicides such as prochloraz-Mn will be useful for strawberry growers and provide more options for controlling anthracnose in Korea.

Comparative Analysis between Healthy and Powdery Mildew-infected Plants of Strawberry Cultivar Seolhyang

Department of Horticulture, Kongju National University, Yaesan 340-702, Korea(Received on February 15, 2012; Revised on May 29, 2012; Accepted on May 31, 2012)We examined the incidence of powdery mildew in strawberry cv. Seolhyang plants, and performed acomparative analysis on the temperature, photosynthesis rate, and nutrient content of healthy and powderymildew-infected plants. Powdery mildew first infected the fruit of the strawberries in mid-January, and thedisease severity increased in both fruits and leaves during the late harvest season. The rate of photosynthesisand leaf temperatures of healthy plants were higher than those of powdery mildew-infected leaves andsignificantly decreased with an increase in the disease severity. The healthy and powdery mildew-infectedplants in the soil analysis were not significantly different in chemical compositions. The leaves of the healthyplants contained lower potassium and higher manganese and chlorophyll concentrations than the powderymildew-infected plants. In particular, manganese was significantly higher in healthy leaves than in infectedleaves. Therefore, the concentrations of potassium, manganese and chlorophyll in strawberry leaves may bean important factor for disease suppression.Keywords : Healthy plant, Manganese, Seolhyang

Control of Fusarium Wilt of the Strawberry Caused by Fusarium oxysporum f. sp. fragariae of Solarization with Compost and Calcium Cyanamide Application

Field experiments were conducted to evaluate the effectiveness of soil solarization at the Nonsan Strawberry Experiment Station, Korea in 2006 and 2008. In in vitro tests, exposure times to achieve an of Fusarium oxysporum f. sp. fragariae were 6.6 days and 5.1 days at and , respectively. A 100% lethal temperature was for the same fungus. For field trials, solarization was conducted during the summer season using polyethylene mulch in a plastic house. The organic matter+calcium cyanamide+solarization treatment increased pH, organic matter, and calcium content compared to those before treatment in soil analysis, but no effect had an urea+solarization treatment. The temperatures at 10 cm depth were different in each treatment and the highest temperature was recorded from July 30 to August 10. The average temperature in organic matter+calcium cyanamide+solarization treatment at 10 cm depth was higher than that in all the other treatments. All solarization treatments reduced the soil population of F. oxysporum f. sp. fragariae at 100% in 2008 relative to the non-treated control. All solarization treatments reduced Fusarium wilt incidence to 0% in 2006 and 2008. The effect of organic matter+calcium cyanamide+solarization against F. oxysporum f. sp. fragariae indicates that there may be future alternatives to traditional solarization for disease control as well as reducing the time needed.

Effect of Nutrition Solution pH and Electrical Conductivity on Fusarium Wilt on Strawberry Plants in Hydroponic Culture

Fusarium wilt on strawberry plants caused by Fusarium oxysporum f. sp. fragariae (Fof) is a major disease in Korea. The prevalence of this disease is increasing, especially in hydroponic cultivation in strawberry field. This study assessed the effect of nutrition solution pH and electrical conductivity (EC) on Fusarium wilt in vitro and in field trials. pH levels of 5.0, 5.5, 6.0, 6.5, 7.0, and 7.5 were assayed in vitro and in field trials. EC levels at 0, 0.5, 0.8, 1.0, and 1.5 dS∙m were assayed in field trials. Mycelial growth of Fof increased with increasing pH and was highest at 25C pH 7 and lowest at 20C, pH 5.0 in vitro. The incidence of Fusarium wilt was lowest in the pH 6.5 treatment and highest in the pH 5 treatment in field trials. At higher pH levels, the EC decreased in the drain solution and the potassium content of strawberry leaves increased. In the EC assay, the severity of Fusarium wilt and nitrogen content of leaves increased as the EC increased. These results indicate that Fusarium wilt is related to pH and EC in hydroponic culture of strawberry plants.

First Report of Dieback Caused by Lasiodiplodia theobromae in Strawberry Plants in Korea

Abstract Dieback in strawberry (Seolhyang cultivar) was first observed during the nursery season (June to September) in the Nonsan area of Korea in the years 2012 and 2013. Initial disease symptoms included dieback on runners, as well as black rot on roots, followed by wilting and eventually blackened, necrotic discoloration in the crowns of daughter plants. A fungus isolated from the diseased roots, runners, and crowns is close to Lasiodiplodia theobromae based on morphological characteristics. Analysis of a combined dataset assembled from sequences of the internal transcribed spacer and translation elongation factor 1- alpha genes grouped nine fungal isolates with the type strain of L. theobromae. The isolates showed strong pathogenicity on strawberry cultivars Kumhyang, Seolhyang, and Akihimae, fulfilling Koch’s postulates. Based on these results, the pathogen responsible for dieback on strawberry plants in Korea was identified as L. theobromae.

Comparison of Environmental-Friendly and Chemical Spray Calendar for Controlling Diseases and Insect Pests of Strawberry during Nursery Seasons

Major diseases and insect pests in nursery season of strawberry were anthracnose, powdery mildew, Fusarium wilt, two-spotted spider mite, and aphids. Environmental-friendly and chemical application schedules can improve diseases and insect pests control with relatively fewer organic and chemical materials inputs compared with spray programs when it’s occurred. Field experiments were performed in 2012 to 2013 according to calendar-based spray programs with environmental-friendly spray calendar (EFSC) and conventional chemical spray calendar (CSC) for controlling diseases and insect pests of strawberry plants cv, Seolhyang during the two nursery seasons. EFSC did reduce the incidence of diseases and insect pests as compared to the nontreated control. Incidence of anthracnose and powdery mildew by EFSC and CSC was similar in 2012 and 2013 seasons. In addition, occurrence of two-spotted spider mite in EFSC in 2013 was similar to those of CSC and was shown highly in early and mid-June both 2012 and 2013 seasons. Occurrence of aphid in EFSC was shown highly in early and mid-June both 2012 and 2013 seasons. These results suggest that EFSC program may be effective for controlling strawberry diseases and insect pests by using environmental-friendly organic materials.