Okhee Choi

Complete Genome Sequence of the Rice Pathogen Pantoea ananatis Strain PA13

Pantoea ananatis is the causative agent of sheath and grain rot in rice. Here, we present the complete genome sequence of P. ananatis strain PA13, originally isolated from a diseased rice grain.

First Report of Botrytis cinerea as a Postharvest Pathogen of Blueberry in Korea

Abstract Gray mold of blueberry caused by Botrytis sp. is reported for the first time in Korea. A detailed description of the fungus is given, along with its rDNA internal transcribed spacer sequence. The fungus was identified as Botrytis cinerea based on mycological characteristics and molecular data.

A simple and sensitive biosensor strain for detecting toxoflavin using β-galactosidase activity

In this study, we developed a simple and sensitive biosensor for the determination of toxoflavin (which is toxic to various plants, fungi, animals, and bacteria) in natural samples based on β-galactosidase activity. The proposed toxoflavin detection method for toxin-producing bacteria or toxin-contaminated foods is simple and cost effective. Burkholderia glumae, a species known to cause rice grain rot and wilt in various field crops, produces toxoflavin under the control of a LysR-type transcriptional regulator ToxR and its ligand toxoflavin. As the expression of toxoflavin biosynthetic genes requires toxoflavin as a co-activator of ToxR, a novel biosensor stain was constructed based on lacZ reporter gene integration into the first gene of the toxoflavin biosynthesis operon, toxABCDE of B. glumae. The biosensor was composed of a sensor strain (COK71), substrates (X-gal or ONPG), and culture medium, without any complex preparation process. We demonstrated that the biosensor strain is highly specific to toxoflavin, and can quantify relative amounts of toxoflavin compared with known concentrations of toxoflavin. The proposed method was reliable and simple; samples containing 50-500 nM of toxoflavin could be analyzed. More importantly, the proposed biosensor strain could identify toxoflavin-producing bacteria in real samples. The excellent performance of this biosensor is useful for diagnostic purposes, such as detecting toxoflavin-contaminated foods and environmental samples.

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.

Spot Anthracnose Disease Caused by Colletotrichum gloeosporioides on Tulip Tree in Korea

The tulip tree (Liriodendron chinense) has been widely cultivated in Korea as a street or garden tree for its large flowers, which have a superficial resemblance to tulips. Occurrence of anthracnose disease on the leaves of tulip trees growing on the campus of Gyeongsang National University, Jinju, Korea, has been observed. Based on mycological characteristics, pathogenicity, and internal transcribed spacer sequence, the causal fungus was identified as Colletotrichum gloeosporioides. This is the first report on anthracnose disease caused by C. gloeosporioides on tulip trees in Korea.

Soft Rot of Rhizopus oryzae as a Postharvest Pathogen of Banana Fruit in Korea

Soft rot on banana fruit caused by Rhizopus oryzae was identified for the first time in Korea. Colonies were white to light brown and formed numerous sporangiospores. Optimum temperature for mycelial growth was 30°C. Sporangia were globose and 30~200 μm. Sporangiophores were usually straight, 8~20 μm, and rhizoids usually in groups of 3~5. Columella were globose to sub-globose and 90~110 μm. Sporangiospores were sub-globose or oval and 4~10 μm. Based on its mycological characteristics, molecular analysis, and pathogenicity to host plants, this fungus was identified as Rhizopus oryzae Went & Prisen Geerligs. This is the first report of soft rot on banana caused by Rhizopus oryzae in Korea.

A Simple and Rapid Method for Functional Analysis of Plant Growth-promoting Rhizobacteria Using the Development of Cucumber Adventitious Root System

Many plant growth-promoting rhizobacteria (PGPRs) have been known for beneficial effects on plants including biological control of soilborne pathogens, induced systemic resistance to plant pathogens, phytohormone production, and improvement of nutrient and water uptake of plants. We developed a simple and rapid method for screening potential PGPR, especially phytohormone producing rhizobacteria, or for analyzing their functions in plant growth using cucumber seedling cuttings. Surface-sterilized cucumber seeds were grown in a plastic pot containing steamed vermiculite. After 7 days of cultivation, the upper part 2 cm in length of cucumber seedling, was cut and used as cucumber cuttings. The base of cutting stem was then dipped in a microcentrifuge tube containing 1.5ml of a bacterial suspension and incubated at with a fluorescent light for 10 days. Number and length of developed adventitious roots from cucumber cuttings were examined. The seedling cuttings showed various responses to the isolates tested. Some isolates resulted in withering at the day of examination or in reduced number of roots developed. Several isolates stimulated initial development of adventitious roots showing more adventitious root hair number than that of untreated cuttings, while some isolate had more adventitious root hair number and longer adventitious roots than that of untreated control. Similar results were obtained from the trial with rose cuttings. Our results suggest that this bioassay method may provide a useful way for differentiating PGPR`s functions involved in the development of root system.

Pink Mold Rot on Unishiu Orange (Citrus unshiu Mac.) Caused by Trichothecium roseum (Pers.) Link ex Gray in Korea

In 2012, a pink mold rot was observed on unishiu orange (Citrus unshiu Mac.) fruits at the Wholesale Market for Agricultural Products, Jinju, Korea. The symptom on unishiu orange was a water-soaked lesion on the surface of fruit, which later on enlarged to form softened brown rot lesions. The diseased fruits were covered with pink-colored mold, consisting of conidia and conidiophores of the pathogen. Optimum temperature for mycelial growth was . Conidia were hyaline, smooth, 2-celled, and thick-walled conidia with truncate bases, ellipsoidal to pyriform, characteristically held together zig-zag chains and in size. Conidiophore was erect, colorless, unbranched, and 4-5 wide. On the basis of mycological characteristics, pathogenicity test, and molecular analysis with complete ITS rDNA region, the causal fungus was identified as Trichothecium roseum (Pers.) Link ex Gray. This is the first report of pink mold rot caused by T. roseum on unishiu orange in Korea.

Sclerotium Rot of Onion Caused by Sclerotium rolfsii

The sclerotium rot of onion (Allium cepa L.) was occurred sporadically in the farmers fields at Daehap, Changnyeong in Korea. The typical symptom was water-soaking on the bulb, stem and leaves and then rotting, wilting, blighting and the infected plants eventually were rotted and died. The sclerotia were globoid, 1�3 mm, and white to brown. The optimum temperature for mycelial growth and sclerotial formation on PDA was 30 C. The hyphal width was 4�9 µm. The typical clamp connections were observed in the hyphae of the fungus grown on PDA. On the basis of mycological characteristics, ITS rDNA sequence analysis, and pathogenicity, this fungus was identified as Sclerotium rolfsii Saccardo. To our knowledges, this is the first report of sclerotium rot on onion caused by S. rolfsii in Korea.

Identification of Lasiodiplodia pseudotheobromae causing mango dieback in Korea

Abstract Mango (Mangifera indica) is an economically important fruit grown in tropical regions. Mango cultivation has increased in Korea as the fruit has become more popular; however, the majority of the fruit is imported. Mango dieback was observed for the first time in July 2016, in Tongyeong, South Korea. The aim of the present study was to identify the causal pathogen. Identification of the fungus was based on morphological and cultural characteristics, and sequencing of the internal transcribed spacer rRNA region and gene encoding translation elongation factor 1-alpha. A phylogenetic analysis of the sequences confirmed that the fungus isolated from diseased mango plants was Lasiodiplodia pseudotheobromae. Koch’s postulates were completed by pathogenicity tests conducted on healthy leaves, fruit and whole plants. Based on the morphological characteristics, pathogenicity tests, and molecular identification, the causal fungus was identified as L. pseudotheobromae. This is the first report of mango dieback caused by L. pseudotheobromae in Korea. The recent occurrence of the disease indicates that the fungus poses a potential threat to mango production in Korea.