|Budget Amount *help
¥6,300,000 (Direct Cost : ¥6,300,000)
Fiscal Year 1995 : ¥1,400,000 (Direct Cost : ¥1,400,000)
Fiscal Year 1994 : ¥1,200,000 (Direct Cost : ¥1,200,000)
Fiscal Year 1993 : ¥3,700,000 (Direct Cost : ¥3,700,000)
Elevated unfiltered UVB inhibited tiller number, biomass production, plant length, photosynthetic rate and chlorophyll content in rice. UVB effects were alleviated either by elevated CO_2 atmosphere or by exposure to high irradiance-visible radiation. Among 5 Asian rice ecotypes (aus, aman, boro, bulu and tjeleh) from Bengal and Indonesia and Japanese lowland and upland rice groups, the Japanese lowland rice group and the boro ecotype were more resistant. Among Japanese lowland rice cultivars, Sasanishiki exhibited more resistance to UVB,while Norin 1 showed less resistance, although these two cultivars are closely related. It was evident that various cultivars having different sensitivities to UVB were involved in the same ecotype and the same group, and that the resistance of rice to UVB is not simply due to the difference in the geographical situation where rice cultivars are cultivated. The genetic analysis of resistance to UVB effects on growth of rice using F2 plants generated by reciprocally crossing Sasanishiki and Nirin 1 and F3 lines generated by self-fertilizing F2 plants proved that the resistance to UVB was controlled by recessive polygenes. Elevated UVB containing no UVC reduced total leaf nitrogen, soluble protein and Rubisco, while increased in the accumulation of UV-absorbing compounds. There was a cultivar difference in the resistance to UVB effects. The reduction in Rubisco content was less in Sasanishiki, while the increase in the accumulation of UV-absorbing compounds was greater in Sasanishiki. It was thus suggested that the cultivar difference in the resistance to UVB might be due to the difference between Rubisco content and UV-absorbing compounds as influenced by UVB.