| Preliminary experiments on the relation between dose
rate and radiation effect in Triticum monococcum T. FUJII National Institute of Genetics, Misima, Japan 10 and 20 kr irradiations with three different dose rates were applied to einkorn wheat seeds. The highest dose rate was 1,000 r/min of X-rays and the lowest was 0.75 r/min of 10 kr and 1.5r/min of 20 kr gamma-radiations. 33 r/min irradiations at 10 and 20 kr were used with X- as well as gamma-rays for the check of RBE differences. Then seedling height, fertility and chlorophyll mutation rate in the X2-generation were examined (Table 1). In all irradiated lots the seedlings were shorter and the fertility of the plants was reduced in comparison with the normal lot, this effect being milder in the batch of lowest dose rate than in the other three irradiated lots. 20 kr lot with the highest dose rate was the most severely damaged and all plants died after germination. The differences were not clear between intermediate and highest dose rates, especially at 10 kr. The higher the dose rate at 10 kr, the higher was the chlorophyll mutation rate in the X2-generation. This tendency was also observed in 20 kr gamma-irradiations. That no mutation was found at the intermediate X-ray dose rate will be due to the small number of X2 head progenies. Similar mutation rates were obtained at 10 kr from the intermediate dose rate in X- and gamma-rays. RBE of X- and gamma-rays was about the same as for mutation rates. |