Hong-Sik Shim

Antagonistic Activities of Bacillus spp. Strains Isolated from Tidal Flat Sediment Towards Anthracnose Pathogens Colletotrichum acutatum and C. gloeosporioides in South Korea.

Anthracnose is a fungal disease caused by Colletotrichum species that is detrimental to numerous plant species. Anthracnose control with fungicides has both human health and environmental safety implications. Despite increasing public concerns, fungicide use will continue in the absence of viable alternatives. There have been relatively less efforts to search antagonistic bacteria from mudflats harboring microbial diversity. A total of 420 bacterial strains were isolated from mudflats near the western sea of South Korea. Five bacterial strains, LB01, LB14, HM03, HM17, and LB15, were characterized as having antifungal properties in the presence of C. acutatum and C. gloeosporioides. The three Bacillus atrophaeus strains, LB14, HM03, and HM17, produced large quantities of chitinase and protease enzymes, whereas the B. amyloliquefaciens strain LB01 produced protease and cellulase enzymes. Two important antagonistic traits, siderophore production and solubilization of insoluble phosphate, were observed in the three B. atrophaeus strains. Analyses of disease suppression revealed that LB14 was most effective for suppressing the incidence of anthracnose symptoms on pepper fruits. LB14 produced antagonistic compounds and suppressed conidial germination of C. acutatum and C. gloeosporioides. The results from the present study will provide a basis for developing a reliable alternative to fungicides for anthracnose control.

Review of Disease Incidences of Major Crops of the South Korea in 2005

In 2004, average temperature was higher, and rainfall was less than those of previous year, The diseases of rice, barley, pepper, chinese melon, apple and oriental pear were surveyed. Seedling diseases, leaf blast, sheath blight and bacterial blight of rice, phytophthova blight, virus diseases and anthracnose of pepper, and sudden wilt syndrome and powdery mildew of chinese melon grown in plastic greenhouse were severe. Especially, sheath blight and bacterial blight of rice occurred two times higher than those of previous year, Panicle blight of rice decreased about 4 times, compared with the previous year, presumed that the lower rainy days, rainfall and RH suppressed spread of the fungal pathogens to panicles of rice. Lower rainfall during mid- and late Aug caused three-times less occurrence of phytophtora blight of red-pepper than that of the previous year, Another diseases surveyed occurred similar or less than those of the previous year.

Damage Analysis of Rice Panicle Blast on Disease Occurrence Time and Severity

The structural differences between healthy and diseasedpanicle necks caused by Pyricularia oryzae were observed using electron-microscope. In the diseased panicle neck, the infection hyphae of the rice blast pathogen grew through the sclerenchymatous fiber tissue and reached to the central internal lacuna. Since the pathogen grew through the sclerenchymatous fiber tissues, the vascular bundle composed with xylem and phloem had been destroyed and finally the nutrients from the leaf and stem were not able to be transported into the grains. Infection of panicle base by the blast pathogen until 20 days after heading caused more than 50% of yield loss in both Jinmibyeo and Chucheongbyeo. There was a positive correlation between incidence of the panicle blast and rice yield losses. The regression equations between incidence of the panicle blast and yield losses were y

Survey of Major Disease Incidence of Rice in Korea during 1999-2008

During the period from 1999 to 2008, we surveyed the major diseases incidence of rice in Korea. Leaf blast showed 0.85% of the diseased leaf area in 2000 and then consistently decreased to 0.02% by 2008. However, panicle blast irregularly appeared by the years depending on weather conditions for disease development from heading to milk stage of rice. Diseased lesion height of sheath blight had the lowest (10.1%) incidence in 2001 and the highest (21.4%) incidence in 2007. A negative corelation (

Establishment of Economic Threshold by Evaluation of Yield Component and Yield Damages Caused by Rice Leaf Blast (Magnaporthe grisea)

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

This study was conducted to decide disease incidence level of rice leaf blast required for reasonable fungicide application in paddy field. We induced the disease development by inoculating rice blast pathogens on rice seedlings (Jinmibyeo) in the greenhouse and transplanting the infected seedlings in the field two weeks after rice plants were transplanted. We scored the disease incidence, grouped and marked according to degree of percentage of diseased leaf area at maximum stage of disease development. The percent diseased leaf area (PDLA) had negative correlations with panicle number per hill, ripened grain (%), and total yield; their correlation coefficients (r), , and , respectively. However, it had positive correlations with spikelets per panicle and thousand grain weight; their correlation coefficients (r), and , respectively. Gain threshold (GT) calculated based on control cost and market price was estimated to be 8.35. Economic injury level (EIL) obtained based on GT and coefficient of damage of regression equation between disease incidence and the different yield components; panicle number per hill, spikelets per panical, ripened grain(%), thousand grain weight and yield were 41.8, 9.7, 19.1, 291.1 and 3.4%, respectively. Economic threshold (ET) for yield was 2.7% () on PDLA. These results suggest that application of fungicide is necessary when two under leaves are almost covered with lesions or contained more than twenty large lesions under leaves at maximum tillering stage.

Bacterial Blight of Shallot, Caused by Pseudomonas syringae pv. porri, a New Disease in Korea

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

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

Shallots (Allium cepa var. ascalonicum L.) affected by bacterialblight disease received for diagnosis in March 2007 (Fig. 1A).Grower has estimated and we have confirmed that as much as two-third of the plant was affected by the disease in fields in the DaejungDistrict, Seokwipo of Jeju, Korea in April, 2007. The symptoms onleaves included yellowish and brownish leaf blight on leaf surface.Seriously infected plants shriveled and died in fields. Two isolates,BC2489 and BC2498 were recovered on trypticase soy agar (TSA)from symptomatic leaves of the plants. Pathogenicity was evaluatedon seven-week-old shallots by spot and spray inoculation. Bacteriawere grown on TSA for 48 h at 28

Various Cultural Factors Associated with Disease Development of Garlic White Rot Caused by Two Species of Sclerotium

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

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

This study was conducted to investigate the control possibility of garlic white rot causing severe yield losses of Allium species and cultivars using cultural practices such as optimal sowing date and burial depth, and lime application. Inoculum density in infested field soil was investigated at different soil depth, and that on the diseased plant debris was done. Inoculum density and recovery ratio of white rot pathogen of garlic was highly different between two species of Sclerotium cepivorum forming comparatively small sclerotia and Sclerotium sp. forming comparatively large ones. It was confirmed that S. cepivorum formed more sclerotia on bulbs of garlic than S. sp., and sclerotial recovery of S. cepivorum was higher than that of S. sp. Inoculum density of white rot pathogen in the infested field at garlic seeding period ranged from one to thirteen sclerotia per 30 g soil. Inoculum density of white rot pathogen decreased remarkably with increasing soil depth and above 95% of sclerotia were distributed within 5 cm of soil depth. Disease severity of white rot was higher on slightly planted garlics than deeply-planted ones. Garlic seed bulbs infected by white rot pathogens were confirmed to be one of main inoculum sources of white rot in the field and the disease incidences caused by garlic seed transmission showed big differences among garlic varieties. When nine garlic varieties harvested from infested plots were sown in the field, highly susceptible varieties, ‘Wando’, ‘Daeseo’, ‘Namdo’ and ‘Kodang’ showed high disease incidences, whereas other five varieties were not infected at all. It was confirmed that white rot occurred higher on early-sown garlics, before middle October, than on late-sown ones, after late October. Meanwhile, increasing application rate of lime ranged from 100 to 300 g reduced disease severity of white rot.