| Differences in effects of gamma-rays and fast neutrons
on wheat Seiji MATSUMURA National Institute of Genetics, Misima, Japan 1. gamma-rays and fast neutrons from Po-Be source on einkorn wheat Fast neutrons were obtained from a Po-Be source. The nuclear reaction is 94Be (Alpha, n) 126C, and 21084 Po, whose half life is 138 days, is used as a Alpha-emitter. The resultant neutrons are emitted as discrete spectrum with the maximum energy of 11 MeV and a mean energy of approximately 7.2 MeV. Dry seeds were attached to the surface of a stainless steel cylinder of 10 cm diameter, which contained the Po-Be neutron source (210 Po 10 c) in the center. The irradiation dose, preliminarily applied to einkorn wheat seeds, ranged from 24 to 125 rad for 3 - 15 days. At the same time gamma-radiations with 137Cs 6,000 c were used for comparison at 5 - 15 kr and 20 kr/hr. Fast neutrons at 24 - 125 rad were not markedly effective in inhibiting seed germination and seedling growth and decreasing survival in the field or seed fertility in X1, but were for chlorophyll mutation effective even at 75 - 125 rad. It is assumed that these neutrons are more effective than 14 MeV neutrons, and the RBE value for chlorophyll mutation frequency is about 40 against gamma-rays. 2. gamma-rays and fission neutrons in the polyploid wheat series Dry seeds of Triticum monococcum flavescens, T. durum Reichenbachii and T. vulgare erythrospermum were subjected on Oct. 21, 1963 to fission neutrons from the ORNL Health Physics Research Reactor, and gamma irradiation from 60Co source was also carried out simultaneously in Oak Ridge National Laboratory by courtesy of Dr. J. A. AUXER. Intensity of gamma-rays in this series was 175 kr/hr. Neutrons were given for 804 seconds to the seeds at various distances from the center of the neutron reactor. The seeds of T. monococcum received dose of 103 - 1,027 rad and those of T. durum and T. vulgare doses of 257 - 2,057 rad. There was approximately 10 % additional exposure due to gamma-rays associated with the neutron field. The data for germination, seedling growth and seed fertility are given for fission neutrons and gamma-radiation in Table 1. In June (harvest season) of 1963 we had unusually abundant rainfall. Therefore the seeds were not good and germination was generally low. The higher was the dose of fission neutrons and gamma-rays, the more delayed were germination and growth of seedlings, and the more reduced was seed fertility. In general, T. monococcum was the most sensitive to fission neutrons and gamma-rays. There was as expected no significant difference between T. durum and T. vulgare. The frequency of spike progenies with chlorophyll mutations in X2 was also investigated, as shown in the last column of Table 1. As expected, the higher was ploidy, the lower was mutation frequency. Only one albina mutation was found in hexaploids. |
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