INHIBITORY EFFECTS OF AMBIENT LEVELS OF SOLAR UV-A AND UV-B RADIATIONON GROWTH OF CUCUMBER

The influence of solar UV-A and UV-B radiation at Beltsville, Maryland , on growth and flavonoid content in four cultivars of Cucumis sativus L. (Ashley, Poinsett, Marketmore, and Salad Bush cucumber) was examin ed during the summers of 1994 and 1995. Plants were grown from seed in UV exclusion chambers consisting of W-transmitting Plexiglas, lined w ith Llumar to exclude UV-A and UV-B, polyester to exclude UV-B, or cel lulose acetate to transmit UV-A and UV-B. Despite previously determine d differences in sensitivity to supplemental UV-B radiation, all four cultivars responded similarly to UV-B exclusion treatment. After 19-21 days, the four cultivars grown in the absence of solar UV-B (polyeste r) had an average of 34, 55, and 40% greater biomass of leaves, stems, and roots, respectively, 27% greater stem height, and 35% greater lea f area than those grown under ambient W-B (cellulose acetate). Plants protected from UV-A radiation as well (Llumar) showed an additional 14 and 22% average increase, respectively, in biomass of leaves and stem s, and a 22 and 19% average increase, respectively, in stem elongation and leaf area over those grown under polyester. These findings demons trate the extreme sensitivity of cucumber not only to present levels o f UV-B but also to UV-A and suggest that even small changes in ozone d epletion may have important biological consequences for certain plant species.