UV-B EFFECTS ON CROPS - RESPONSE OF THE IRRIGATED RICE ECOSYSTEM

Increasing ultraviolet-B (UV-B) radiation resulting from depletion of the stratospheric ozone layer could have damaging effects on crops. Th is paper reviews recent findings on direct effects of UV-B on rice gro wth and yield as well as indirect effects via impacts on other organis ms in the rice (Oryza sativa) agroecosystem. The findings are based on research by scientists at the International Rice Research Institute ( IRRI) in Los Banos, the Philippines, and their collaborators in China and the United States; with comparison to research by scientists in ot her countries. Current results indicate that while enhanced UV-B direc tly impacts many aspects of rice growth, physiology, and biochemistry under controlled phytotron conditions; in general rice growth and yiel d are not affected under natural field conditions. The difference in r esponse may be related both to the levels of UV-B exposure used in phy totron vs. field studies and the lower ratio of UV-A to UV-B in the ph ytotron compared to field. In terms of indirect effects on rice blast disease, enhanced UV-B affected both the fungus itself (Pyricularia gr isea) and the susceptibility of the rice plant to the fungus. Based on these data, simulation models estimated potential impacts of higher U V-B levels on blast severity and rice yield in different countries of southeast. and east Asia. Ultimately results from rice studies can be used to identify strategies to minimize any negative effects of UV-B o n rice productivity.