PHOTOSENSITIVITY OF CUCUMBER (Cucumis sativus L.) SEEDLINGS EXPOSED TO ULTRAVIOLET-B RADIATION

The intensity of ultraviolet-B radiation (UV-B) has increased on the Earthʹs surface due to the stratospheric ozone depletion, causing an adverse effect on a wide range of species, such as morphological, physiological, and biochemical alterations. This research studied the intraspecific photosensitivity of cucumber (Cucumis sativus L.) seedlings exposed to UV-B. Six commercial cultivars were evaluated: Laura, Sprint 440, Dasher II, Exocet, Poinsett 76, and Marketmore 76 under greenhouse-controlled environmental conditions with a hydroponic sandwich-type system with a Hoagland II nutrient solution. Seedlings were irradiated from expanded cotyledons to the third true leaf with three intensities of UV-B radiation (30, 40, and 50 p,W cm-2) for 18 d between 11:40-15:40 h. Seedling growth, morphology, accumulation of photosynthetic pigments, and absorbing UV-B pigments were evaluated. ʹLauraʹ was the least affected by chlorosis and had a total absence of leaf curl, whereas ʹPoinsett 76ʹ was the most affected in the 40 and 50 p,W cm-2 intensities. Both leaf area and seedling height of ʹMarketmore 76ʹ and ʹPoinsett 76ʹ had the lowest values. ʹLauraʹ obtained the highest value in both fresh weight and dry weight. ʹPoinsett 76ʹ had the least amount of pigments absorbing UV-B and was 53% lower than that obtained by ʹLauraʹ. ʹPoinsett 76ʹ had lower chlorophyll and carotenoids. Parameters used were indicators of the seedling response to UV-B radiation, but could not be used for cucumber seedling sensitivity to UV-B radiation.