Screening of Resistant Watermelon Cultivars Against Gummy Stem Blight Fungus, Didymella bryoniae, and Comparison of Protein Expression Between Cultivars After Infection

수박 덩굴마름병의 품종 저항성 검정과 감염 후 품종간 단백질 발현의 비교

Since the leaf inoculation procedures are time-consuming and require considerable growth chamber space, a rapid dioassay method for screening of pathogenicity of Didymella bryoniae, a casual agent of gummy stem blight in watermelon, was established in this paper. The method produced reliable results within 8 days ( 5 days for growing seedlings and 3 days for rapid disease response in the seedlings). After contaminants in the root of 4~5 day-old seedlings had been washed using sterilized water, 5 seedlings were dipped into a vial containing 12 ml of conidial suspension (106 cells/ml). After the vials were placed in a growth chamber (22$^{\circ}C$, RH 50%, 14hr light/10hr darkness) for 3 days, susceptibility and resistance of cultivars were determined by the degree of disease response on cotyledon. The result of obtained by the dip-inoculation method was well coincided with the results by the leaf inoculation procedures and the result that had been observed for several years in the field. Screening of collected watermelon cultivars by the dip-inoculation method revealed that all the 21 domestic cultivars collected were susceptible and only 3 foreign cultivars (PI 189225, PI 482322 and IT 188207) were resistant among 18 cultivars A cucumber cultivar (Marketer) and bitter cucumber were proven to be resistant against the D. bryoniae among 8 other different cucurbits tested. The SDS-PAGE patterns of total proteins from a susceptible (Keumcheon) and a resistant (PI 189225) watermelon cultivars were compared 0, 12, 24 and 36 hrs after inoculation. The amounts of two distinct protein bands (24 kDa and 70 kDa) were gradually increased after inoculation in both cultivars.