Radiation Genetics in Wheat, VI: Biological Effects of Thermal and Fast Neutrons on Diploid Wheat

The thermal and fast neutron irradiations of dormant seeds of Triticum monococcum flavescens were conducted in the Japan Atomic Energy Research Institute's Nuclear Reactor, JRR-1, and in the Oak Ridge National Laboratory's accelerator (14MeV), respectively. The higher was the dosage of the thermal and fast neutrons, the more delayed were germination and growth of seedlings. The seeds were almost uniformly injured in each treatment. There was almost no germination at 37.5×1012nth/cm2 of thermal neutrons and at 5krad fast neutrons. Even at about 30×1012nth/cm2 and at 2.5krad the seedlings did not grow and died in early stage. Also the higher the dosage, the more reduced were survival rate, height of mature plants, and seed fertility. The frequency of chromosome aberrations and chlorophyll and other mutations increased with the increase of dosage, as expected. In comparison with the results obtained from X- and gamma-irradiations, 1r equivalent effects of X-rays are produced by about 2×109nth/cm2 of thermal neutrons for seedling length and seed fertility. Also the 1r equivalent effects correspond roughly to those of the order of 109nth/cm2 for chromosome aberrations and chlorophyll mutations. The relative biological effectiveness (RBE) of fast neutrons to X-rays was found to be for germination rate 4, for seedling length 10, for seed fertility 12, for chromosome aberrations 8 and for chlorophyll mutations 10.