Sang Yeob Lee

Induced Systemic Resistance by Bacillus vallismortis EXTN-1 Suppressed Bacterial Wilt in Tomato Caused by Ralstonia solanacearum

【Biocontrol activity of five strains of selected rhizo-bacteria were tested in tomato against bacterial wilt caused by Ralstonia solanacearum. After root bacterization the plants were grown in a perlite-hydroponic system. Upon challenge inoculation with the pathogen, all of the rhizobacterial strains efficiently suppressed the bacterial wilt in tomato in various rates, at maximum by the strain, Bacillus vallismortis strain EXTN-1. While the percent of infected plants in the non-bacterized control plants were 95%, it was only 65% in plants pre-treated with EXTN-1. It was also demonstrated that the movement of R. solanacearum within the stem was significantly hampered when the plants were root bacterized. As EXTN-1 has no antagonistic properties against R. solanacearum, the bacterial wilt was probably suppressed by a mechanism other than antibiosis. Previously, the strain had been proven to produce an efficient elicitor for inducing systemic resistance in many crops. As the present study confirmed that EXTN-1 has the ability for reducing the pathogen spread in tomato, the strain could be effectively used as a potential biocontrol agent against bacterial wilt.】

Morphology, Molecular Phylogeny and Pathogenicity of Colletotrichum panacicola Causing Anthracnose of Korean Ginseng

Colletotrichum panacicola isolates were obtained from anthracnose lesions of Korean ginseng and compared with four Colletotrichum species in morphology, molecular phylogeny and pathogenicity. Based on morphological characteristics, C. panacicola was easily distinguished from Colletotrichum gloeosporioides but not from Colletotrichum higginsianum, Colletotrichum destructivum and Colletotrichum coccodes. A phylogenetic tree generated from ribosomal DNA-internal transcribed spacer sequences revealed that C. panacicola is remarkably distinguished from C. gloeosporioides and C. coccodes but not from C. higginsianum and C. destructivum. However, molecular sequence analysis of three combined genes (actin + elongation factor-1α + glutamine synthatase) provided sufficient variability to distinguish C. panacicola from other Colletotrichum species. Pathogencity tests showed that C. panacicola is pathogenic to Korean ginseng but not to other plants. These results suggest that C. panacicola is an independent taxon distin-zguishable from C. gloeosporioides and other morphologically similar Colletotrichum species.

Novel Oxidized Derivatives of Antifungal Pyrrolnitrin from the Bacterium Burkholderia cepacia K87

The screening of antifungal active compounds from the fermentation extracts of soil-borne bacterium Burkholderia cepacia K87 afforded pyrrolnitrin (1) and two new pyrrolnitrin analogs, 3-chloro-4-(3-chloro-2- nitrophenyl)-5-methoxy-3-pyrrolin-2-one (2) and 4-chloro-3-(3-chloro-2-nitrophenyl)-5-methoxy-3-pyrrolin-2-one (3). Pyrrolnitrin showed strong antifungal activity against Rhizoctonia solani but the analogs (2 and 3) were found to be marginally active. The isolates, 2 and 3, are believed to be biodegraded derivatives of pyrrolnitrin.

Microbial Diversity and Community Analysis in Lettuce or Cucumber Cultivated Greenhouse Soil in Korea

The soil chemical properties, microbial community structures and biochemical properties of lettuce or cucumber-cultivated greenhouse soil samples were analyzed to assess soil health and characterize microbial distribution in 8 locations in Korea. Although most of chemical properties were within the soil management guidelines, the available phosphate, and the contents of exchangeable potassium and calcium were higher than those of recommended levels. In the culture-dependent analysis, 841 bacterial strains were isolated from the greenhouse soils and were identified at the genus level by 16S rRNA gene sequences analysis. The dominant bacterial genera were Bacillus (35.7%), Microbacterium (9.3%), Arthrobacter (5.7%) and Lysobacter (5.1%). The abundance of pseudomonads was highly variable depending on the soil samples. In the culture-independent analysis, soil microbial community was investigated by using phospholipid fatty acid (PLFA) method. Principal component analysis (PCA) showed that a specific grouping for microbial community structure in the greenhouse soils was not observed based on cultivated crops and investigated sites. The results revealed that the greenhouses soils examined are relatively sound managed in terms of soil chemical contents and microbial properties.

Virulence of Entomopathogenic Fungi Metarhizium anisopliae and Paecilomyces fumosoroseus for the Microbial Control of Spodoptera exigua

Abstract The beet armyworm Spodoptera exigua (Lepidoptera: Noctuidae) is difficult to control using chemical insecticides because of the development of insecticide resistance. Several pest control agents are used to control the beet armyworm. Entomopathogenic fungi are one of the candidates for eco-friendly pest control instead of chemical control agents. In this study, among various entomopathogenic fungal strains isolated from soil two isolates were selected as high virulence pathogens against larva of beet armyworm. Control efficacy of fungal conidia was influenced by conidia concentration, temperature, and relative humidity (RH). The isolates Metarhizium anisopliae FT83 showed 100% cumulative mortality against second instar larvae of S. exigua 3 days after treatment at 1 × 107 conidia/mL and Paecilomyces fumosoroseus FG340 caused 100% mortality 6 days after treatment at 1 × 104 conidia/mL. Both M. anisopliae FT83 and P. fumosoroseus FG340 effectively controlled the moth at 20~30°C. M. anisopliae FT83 was significantly affected mortality by RH: mortality was 86.7% at 85% RH and 13.4% at 45% RH. P. fumosoroseus FG340 showed high mortality as 90% at 45% RH and 100% at 75% RH 6 days after conidia treatments. These results suggest that P. fumosoroseus FG340 and M. anisopliae FT83 have high potential to develop as a biocontrol agent against the beet armyworm.

Leaf Spot and Stem Rot on Wilford Swallowwort Caused by Stemphylium lycopersici in Korea

In June 2012, leaf spot and stem rot were observed on Wilford Swallowwort plants grown in Cheonan, Korea. Three fungal isolates obtained from the diseased leaves and stems were identified as Stemphylium lycopersici, based on morphological, cultural, and molecular characteristics and pathogenicity. This is the first report of leaf spot and stem rot on Wilford Swallowwort caused by S. lycopersici.

Influence of Additives on the Yield and Pathogenicity of Conidia Produced by Solid State Cultivation of an Isaria javanica Isolate

Abstract Recently, the Q biotype of tobacco whitefly has been recognized as the most hazardous strain of Bemisia tabaci worldwide, because of its increased resistance to some insecticide groups. As an alternative control agent, we selected an Isaria javanica isolate as a candidate for the development of a mycopesticide against the Q biotype of sweet potato whitefly. To select optimal mass production media for solid-state fermentation, we compared the production yield and virulence of conidia between 2 substrates (barley and brown rice), and we also compared the effects of various additives on conidia production and virulence. Barley was a better substrate for conidia production, producing 3.43 × 1010 conidia/g, compared with 3.05 × 1010 conidia/g for brown rice. The addition of 2% CaCO3 + 2% CaSO4 to barley significantly increased conidia production. Addition of yeast extract, casein, or gluten also improved conidia production on barley. Gluten addition (3% and 1.32%) to brown rice improved conidia production by 14 and 6 times, respectively, relative to brown rice without additives. Conidia cultivated on barley produced a mortality rate of 62% in the sweet potato whitefly after 4-day treatment, compared with 53% for conidia cultivated on brown rice. The amendment of solid substrate cultivation with additives changed the virulence of the conidia produced; the median lethal time (LT50) was shorter for conidia produced on barley and brown rice with added yeast extract (1.32% and 3%, respectively), KNO3 (0.6% and 1%), or gluten (1.32% and 3%) compared with conidia produced on substrates without additives.

Identification of Microdochium bolleyi Associated with Basal Rot of Creeping Bent Grass in Korea

Symptoms of basal rot occurred sporadically on creeping bent grasses growing at a golf course in Hampyeong, Korea in April 2007. Ten isolates of Microdochium sp. were obtained from leaves and crowns of the diseased bent grasses. All isolates were identified as Microdochium bolleyi based on morphological, cultural, and molecular characteristics. This is the first report on M. bolleyi associated with basal rot on creeping bent grass in Korea.

Occurrence of Stem-end Rot on Mango Fruits Caused by Lasiodiplodia theobromae in Korea

Mango ( Mangifera indica L.), an economically important fruit cropin the subtropics and tropics, was recently introduced into Korea. Itis being cultivated over an area of 20 ha with an annual productionof approximately 300 tons in Jeju Island. In July 2010, stem-end rotswere found on fruits of mango (cv. Irwin) grown in a greenhouse inJeju. In the early stage, the affected fruits appeared as small brownspots. As they enlarged, the lesions became circular, dark brown toblack and water-soaked patches and progressed from the surface toinner part of the fruit (Fig. 1A). Two fungal isolates were obtained from lesions on mango fruits.Cultures were initially white to smoke grey, with fluffy aerialmycelium on potato dextrose agar and became gray or black with afew medium grays in laterstage (F ig.1B) . The pycnidia produced onthe 14-day-old cultures (Fig. 1C) were simple, often aggregated,stromatic, ostiolate and hairy. Paraphyses within the pycnidia werehyaline,cy lindrica septate, occasionallyl, branched. Conidiogenouscells were hyaline, thin-walled, smooth, cylindrical, holoblastic(Fig. 1D). Young conidia were hyaline, unicellular and subovoid toellipsoid, with a granular content (Fig. 1E). Mature conidia wereone-septate, dark brown, thick walled, ellipsoidal, with longitudinalstriations (Fig. 1F) and measured 17.5 −26.8 × 12.3 −17.1 μm (mean22.7 × 14.7 μm). No teleomorph was observed in culture. The twofungal isolates were identified as Lasiodiplodia theobromae (Pat.)Griffon & Maubl. [Synonym: Botryodipodl ia theobromae Pat].bas edon their morphological and cultural characteristics, and correspondedto previous description for the species (Alves et al., 2008).To confirm the identification, the complete internal transcribedspacer (ITS) rDNA regions and translation elongation factor 1-alpha (EF1-α) of the two fungal isolates, ML1001 and ML1005were amplified using the primers ITS1/ITS4 and EF1-688F/EF1-1251R asd escribed by Alvese at . (20l 08) and sequencedTh . ere sultingsequences were deposited in GenBank (Accession numbersJN542561 and JN542562 for ITS rDNA, JN542563 and JN542564for EF1-α). Sequences of reference isolates were retrieved fromGenBank. A phylogenetic tree derived from combined sequences ofITS rDNA and EF1-α was constructed by the neighbor-joiningmethod with Kimura’s two-parameter distance model using MEGAversion 5.0. In the phylogenetic tree, the present isolates placed inthe same clade with L. theobromae in GenBank and clearlydistinguished from the closely related Lasiodiplodia species, L.parva and L. pseudotheobromae (Fig. 2).Pathogenicity tests were made on mango fruits. The fruits wereperforated with 3 mm cork borer, followed by drop-inoculated with100 μl of conidial suspensions (5×10

Occurrence of Gray Mold on Blueberry Trees Caused by Botrytis cinerea in Korea

Gray mold symptoms were frequently observed on green twigs, blossoms, leaves, and fruits of blueberry trees grown in greenhouses in Cheongyang, Dangjin, Daejeon, and Jeju during disease survey in eight locations of Korea from 2007 to 2010. The disease symptoms were not observed in the fields of the other locations investigated. The disease incidence ranged 1~30% in the greenhouses investigated. A total of 27 single spore isolates of Botrytis species were obtained from the gray mold symptoms, and all the isolates were identified as Botrytis cinerea based on their morphological and cultural characteristics. Four isolates of the fungus were tested for pathogenicity to leaves of four varieties of blueberry trees by artificial inoculation with conidial suspensions. All the tested isolates caused gray mold symptoms on the leaves, which were similar to those observed in the greenhouses. This is the first report that B. cinerea causes gray mold of blueberry trees grown in greenhouses in Korea.