Resistance reactions of Cucumis melo to inoculation with Pseudoperonospora cubensis

Reactions of several cultivars and breeding lines of melons to artificial inoculation at the seedling stage with a local isolate of Pseudoperonospora cubensis were compared under growth chamber and field conditions. Four different reactions were distinguishable: highly susceptible, susceptible, partially resistant and resistant. The differences in the reactions were more clear-cut under growth chamber conditions. Selection for resistance could be carried out at the seedling stage using sporangia production and lesion size, shape, colour and number as criteria. Under growth chamber conditions, plants of resistant lines had minimal sporangia production and circular or angular lesions 1–2 cm in diameter which became necrotic within 5 days after inoculation.