EVALUATION OF RESISTANCE TO AND TOLERANCE OF POWDERY MILDEW BY CUCUMBER

Development of powdery mildew (Sphaerotheca fuliginea (Schlecht.: Fr.) Polacci f. sp. fuliginea) on cucumber (Cucumis sativus L.) varieties with different levels of powdery mildew resistance was investigated. P lants were grown in a glasshouse and artificially inoculated with the pathogen. Two types of powdery mildew resistance became obvious. A hig h level of resistance was observed in commercial varieties which suffe r from chlorosis during periods of low light intensity. Resistance cha racterized by stem resistance and only partial leaf resistance was obs erved in one variety. This variety also tolerated high inoculum pressu re, giving yields comparable to those of highly resistant varieties. E xploitation of this tolerance should allow use of fungicides to be red uced without associated problems of leaf chlorosis in spring and autum n crops. An F1-hybrid between resistant and susceptible parents was in distinguishable from the susceptible varieties.