COMPARATIVE STUDY OF SELECTED CUCUMBER CULTIVARS RESISTANT TO POWDERY MILDEW CAUSED BY Sphaerotheca fuliginea

Powdery mildew is a widely distributed and damaging disease of cucurbits worldwide. In the present study, 20 cucumber cultivars were infected with Sphaerotheca fuliginea under controlled conditions. The plants were then evaluated for resistance to the pathogen by visually assessment of disease symptoms. Additionally, five of the infected cultivars with different resistance response were further assessed in terms of leaf chlorophyll florescence emission. Based on the visually assessments a number of 5 cultivars, all belonging to greenhouse class, were identified as resistant, 4, belonging to outdoor class, as susceptible and the others as tolerant. Leaf chlorophyll fluorescence analysis revealed a significant photosynthesis apparatus damage caused by the infection on susceptible but not on resistant cultivars. Particularly, the vitality index (Fv/Fm) representing the maximum efficiency of PS II in conversion of absorbed light to chemical energy and Fv/Fo providing an estimation of the capacity of photosynthesis, decreased only in the infected compared to the healthy leaves of the susceptible cultivars. Conclusively, the two greenhouse cultivars CLE and Green Magic were identified as most resistant cultivars and are suggested to be used to control powdery mildew in greenhouse cultures.