Effects of Enhanced Ultraviolet-B Radiation with a Modulated Lamp Control System on Growth of 17 Rice Cultivars in the Field.

Abstract

To investigate the effects of enhanced UV-B radiation on the growth of rice, 17 lowland cultivars from a variety of geographical regions were pot-grown for two months in the field under eight 40W fluorescent sunlamps filtered with 0.13mm thick cellulose diacetate film (Transmission down to 290nm) in Tsukuba, Japan (360°01′N, 140°07′E, 25m elevation). As a control, 0.13mm thick Mylar D film, which effectively absorbs radiation below 320nm, was used in place of the cellulose diacetate film. Output of the UV lamps in the field was supplied by a feedback control system throughout the day to provide a supplemental levels proportional to ambient solar UV-B. UV-B irradiance weighted with generalized plant response action spectrum normalized at 300nm (UV-BBE) was controlled to 2.67 tims control plots at the plant height from August 25 to October 22, 1992. No significant effects of the two-month supplemental UV-B irradiation treatment were detected on any growth parameters for all the cultivars. For example, plant height, tiller number, heading date and dry weight of whole plants were unaffected by extremely high UV-B irradiation. On the other hand, the concentration of UV-absorbing compounds and chlorophyll in rice leaves exposed to supplemental UV-B tended to increase in many cultivars, although these differences were not statistically significant except a few cultivars.