| Radiation effects of fast and thermal neutrons on wheat
: III. Relation between ploidy and radiation effects S. MATSUMURA and M. NEZU National Institute of Genetics, Misima, Japan Thermal neutron irradiations for Triticum durum and T. vulgare were conducted by the Reactor JRR-1, as in the case of T. monococcum. Exposure to fast neutrons of 14MeV in ORNL was simultaneously carried out with T. monococcum, T. durum and T. vulgare. The dosage ranged from 2.5 to 20 krad for T. durum and T. vulgare. After exposure to 37.5 x 1012 nth/cm2 (V) of thermal neutrons and 5 krad of fast neutrons, T. monococcum did not germinate, while the seeds of T. durum and T. vulgare germinated but most of the seedlings died in an early stage. At 20.6 x 1012 nth/cm2 (IV) of thermal neutrons and 2-2.5 krad of fast neutrons most of the seedlings of T. monococcum died, while in T. durum and T. vulgare slow growth of the seedlings continued. The higher was the dosage of thermal and fast neutrons, the more delayed were germination and growth of seedlings and the more reduced were survival rate, height of mature plants and seed fertility. These relationships were ascertained in T. durum and T. vulgare, as well as in T. monococcum. In general, T. monococcum is the most sensitive to thermal and fast neutrons and T. durum is unexpectedly the most resistant. There is no significant difference between T. durum and T. vulgare. The 1r equivalent effects produced by thermal neutrons are calculated for 2x, 4x and 6x species as Table 1 shows, in comparison with the results obtained by X- and gamma-irradiations in ORNL at 10 and 20 kr. RBE of fast neutrons is calculated as shown in Table 2, in comparison with X- and gamma-rays. RBE is lower for the characters observed in earlier stages (germination rate, length of seedlings) than those of mature plants (seed fertility, chromosome aberrations), especially in polyploids. |