Abstract
Recently much concern has been raised about stratospheric ozone depletion and the possible impact of enhanced UV-B radiation on agriculture and terrestrial ecosystems. The present study was conducted to determine the relationship between growth of crop and UV-B radiation levels and to compare the sensitivity of some species to UV-B. Cucumber (Cucumis sativus L. cvs. Suyo and Shimoshirazu-jibaikyuuri), radish (Raphanus sativus L. cv. Comet) and kidney bean (Phaseolus vulgaris L. cv. Gintebo) seedlings were grown for 2 to 4 weeks in naturally-lit, environmentally controlled glass chambers under UV-B (290-320nm) irradiation from six 20 W-fluorescent sunlamps using 0.10mm polyvinyl chloride sheeting and UV-B free control condition using 3mm acrylic plate. Plants were irradiated three levels (61, 91 and 153mWm-2) of biologically effective ultraviolet-B (UV-BBE) radiation using the generalized plant response action spectrum normalized at 300nm for 10h (0700 to 1700) daily. The levels of UV-BBE employed in this study were similar to or less than that normally incident at Tsukuba (36°N latitude) during clear sky conditions in summer.
Visible foliar injury by UV-B irradiation occurred only in cucumber plants. The typical foliar symptoms were large yellow lesions to the leaf margin of the first, second and third true leaves. Irradiation of high level UV-BBE 153mWm-2 reduced significantly leaf area and dry weight of whole plant in cucumber (cv. Suyo) by 54 and 53% compared to that of the control plants at 2 weeks, respectively. Even irradiation of low level UV-BBE 61mWm-2 reduced significantly leaf area and dry weight of whole plant in Shimoshirazu-jibaikyuuri but these parameters were unaffected in Suyo. On the other hand, growth of radish grown under UV-BBE 153mWm-2 for 3 weeks and kidney bean grown under UV-BBE 91mWm-2 for 3 weeks were significantly unaffected except for radish at 3 weeks. These results suggest that UV-B irradiation at ambient level may inhibit growth in some UV-sensitive plants such as cucumber.
