INTRASPECIFIC VARIATION IN SENSITIVITY TO UV-B RADIATION IN RICE

Twenty-two cultivars of rice (Oryza sativa L.) from diverse origins we re grown under greenhouse conditions and exposed to ultraviolet-B radi ation (U-B; 280-320 nm) simulating a 5% reduction in stratospheric ozo ne in spring for the Philippines (14-degrees N lat.) to evaluate growt h and morphological responses to UV-B. In comparison to controls that received no UV-B, plants exposed to UV-B exhibited significantly reduc ed dry matter production (total plant and shoot), shoot height, leaf b lade length and total leaf area, increased number of tillers, and grea ter weight fractions in leaf blades and roots. For most cultivars, the relative effects of UV-B on shoot morphology were greater than the ef fects on biomass production. The direction of the UV-B effects were ge nerally similar for all cultivars, however, there were significant dif ferences among cultivars in the magnitude of the UV-B-induced changes. Upland cultivars (IRAT104 and OS4) and two low-land cultivars commonl y planted in the USA (Star Bonnet and Lemont) were found to be least a ffected by the UV-B, whereas modern, high yielding, lowland cultivars developed in the Philippines (IR52, IR35546-17-33, and IR58) were foun d to be among the most sensitive to UV-B. Our results indicate that in rice, as in other grasses, shoot morphology may be more responsive to solar UV-B change than plant productivity. Intraspecific variation in morphological responses to UVB could contribute to differences among cultivars in susceptibility to UV-B-induced changes in competitive bal ance between rice and associated weeds of the rice agroecosystem.