Development of an efficient method of screening for watermelon plants resistant to Fusarium oxysporum f. sp. niveum.
This study was conducted to establish an efficient screening method for watermelon plants resistant to Fusarium wilt (FW), which is caused by Fusarium oxysporum f. sp. niveum (Fon). An HA isolate was prepared from a wilted watermelon plant in Haman-gun and identified as F. oxysporum f. sp. niveum based on morphological characteristics, molecular analyses of ITS (internal transcribed spacer) and TEF (translation elongation factor la) sequences, and host specificity on cucurbits including watermelon, melon, oriental melon, and cucumber. The assay for disease response of watermelon differentials indicated that the HA isolate was race 0. Among seven liquid media tested, the highest amount of Fon spores was produced from V8-juice broth, which was selected as a medium for mass production of Fon. The disease assay for 21 watermelon and 11 watermelon-rootstock cultivars demonstrated that 20 watermelon cultivars except for 'Soknoranggul' were susceptible; 'Soknoranggul' was moderately resistant All the tested rootstock cultivars were highly resistant to the HA isolate. The evaluation of disease development depending on various conditions suggested that an efficient screening method for FW resistance in watermelon plants is to dip the roots of 10-day-old seedlings in spore suspension of 1.0×105-1.0×106 conidia.mL-1 for 30 min., to transplant the seedlings to plastic pots with a fertilized soil, and then to cultivate the plants at 25°C for 3 weeks.