Abstract
The effect of chronic gamma ray irradiation on the growth and grain filling of soybean cultivar ‘Enrei’ was investigated. In the Gamma Field (Hitachiomiya, Japan) soybean plants were irradiated with gamma rays at a dose rate about 2.4 Gy/day for 1−4, 8 or 12 weeks from the seedling stage, 1−4 or 8 weeks from the flowering stage and 1−4 weeks from the middle of the maturing stage. Irradiation from the maturing stage did not decrease the number of seeds. However, irradiation from the seedling or flowering stage decreased the number of seeds with increasing irradiation period and 4-week irradiation slightly less than 50 Gy in total, reduced the seed number to one-third of the control. The reduction of seeds number by irradiation from the seedling stage was caused by the inhibition of growth at the early growth stage, but that from the flowering stage resulted from the increase in the number of unfilled pods. Irradiation for all growing periods increased the number of unfilled pods and reduced the number of seeds extremely when the dose exceeded 1.1 Gy/day (120 Gy in total).
