Resistance Characteristics of Watermelon Cultivars to Gummy Stem Blight

Gummy stem blight caused by Didymella bryoniae is one of the diseases that cause significant economic losses in watermelon cultivation. To define the resistance characteristics of watermelon cultivars to D. bryoniae, we investigated virulence of six D. bryoniae isolates in three susceptible cultivars of watermelon. And, we selected six moderately resistant and less susceptible watermelon cultivars to D. bryoniae and investigated occurrence of gummy stem blight on seedlings of the cultivars caused by six isolates of D. bryoniae. The isolates represented different virulence in the susceptible cultivars to the fungus. Occurrence of gummy stem blight on the resistant watermelon cultivars caused by each isolate was positively correlated with the virulence of D. bryoniae isolates. And the number of resistant watermelon cultivars to each isolate of D. bryoniae was decreased according to virulence increase of the fungal isolates. Taken together, these results suggest that resistance of watermelon cultivar to D. bryoniae are likely affected by the virulence of D. bryoniae isolates, but not resulted from race differentiation.