• Research in Plant Disease
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• v.22 no.2
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• pp.72-80
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• 2016

Gummy stem blight, caused by the fungus Didymella bryoniae, is major disease of watermelons worldwide. The objective of the present study was to establish an efficient screening system to identify watermelon resistant to D. bryoniae. An GSB3 isolate was prepared from a watermelon plant showing typical symptoms of gummy stem blight in Haman-gun and identified as D. bryoniae based on molecular analysis of internal transcribed spacer sequence. A simple mass-production technique of inoculum was developed based on spore production of D. bryoniae GSB3 under several incubation conditions and their virulence on watermelon plants. Resistance degrees of 22 commercial watermelon cultivars to the GSB3 isolate were evaluated. Among them, four watermelon cultivars showing different degree of resistance response were selected for further study. Development of disease on the cultivars according to various conditions including inoculum concentrations, incubation periods in dew chamber, and incubation temperatures was investigated. From the results, we suggest an efficient screening method for resistant watermelon cultivars to gummy stem blight. Seeds of watermelon cultivar are sown and grown in a greenhouse until plant stage of 2-fully expanded leaves. Seedlings are inoculated with D. bryoniae by spraying spore suspension of the fungus at a concentration of $5.0{\times}10^5spores/ml$. The infected plants are incubated in humidity chamber at $25^{\circ}C$ for 48 hours and then transferred to a growth chamber at $25^{\circ}C$ and 80% relative humidity with 12-hour light a day. Three to four days after inoculation, disease severity of the plant are measured using percentage of infected leaf area.

• The Journal of Engineering Geology
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• v.23 no.3
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• pp.201-216
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• 2013

Ground penetrating radar (GPR) surveys were conducted in a sand tank model in a laboratory and at an alluvial field site to detect the groundwater table and to investigate the influence of saturation on GPR response in the unsaturated zone. In the sand tank model, the groundwater table and saturation in the sand layer were altered by injecting water, which was then drained by a valve inserted into the bottom of the tank. GPR vertical reflection profile (VRP) data were obtained in the sand tank model for rising and lowering of the groundwater table to estimate the groundwater table and saturation. Results of the lab-scale model provide information on the sensitivity of GPR signals to changes in the water content and in the groundwater table. GPR wave velocities in the vadose zone are controlled mainly by variations in water content (increased travel time is interpreted as an increase in saturation). At the field site, VRP data were collected to a depth of 220 m to estimate the groundwater table at an alluvial site near the Nakdong river at Iryong-ri, Haman-gun, South Korea. Results of the field survey indicate that under saturated conditions, the first reflector of the GPR is indicative of the capillary fringe and not the actual groundwater table. To measure the groundwater table more accurately, we performed a GPR survey using the common mid-point (CMP) method in the vicinity of well-3, and sunk a well to check the groundwater table. The resultant CMP data revealed reflective events from the capillary fringe and groundwater table showing hyperbolic patterns. The normal moveout correction was applied to evaluate the velocity of the GPR, which improved the accuracy of saturation and groundwater table information at depth. The GPR results show that the saturation information, including the groundwater table, is useful in assessing the hydrogeologic properties of the vadose zone in the field.