| Gene mutation in Einkorn wheat induced by X-rays By S. MATSUMURA and T. FUJII National Institute of Genetics, Misima In order to study the relation between the frequency of gene mutations and the dose or wave length of X-rays, dormant seeds of Triticum monococcum were exposed to X-rays at 180 KVP, 3 mA, without a filter. The doses ranged from 5,400 to 13,500 gamma units. The data are shown in Table 1. The frequency of head progenies with induced mutations in the X2-generation increases with X-ray dosage in a linear relation. There was some difference in the sensitivity to X-rays between two varieties, flavescens and vulgare. At the same dosage (8,100gamma) and target distance, but with varying kilovoltage (80-180 KVP) and time of exposure, the mutation frequency was increasing with the decrease of wave length, but not in a linear relation (Tab. 1). As to the difference in sensitivity between the two varieties, the results above mentioned have been confirmed. The relation of mutation rate to X-ray quality was generally in good accord with the results of previous experiments concerned with the frequency of chromosome aberrations (MATSUMURA 1951). These facts can be explained on the basis of the difference in the distribution of ionization within the nuclei and the chromosomes. At irradiation by hard X-rays, the majority of the resulting ionization is more scattered than when soft X-rays are used. About 70% of the mutants were chlorophyll abnormalities, about half of which were albina and the other half chlorina, virido-albina, basi-viridis, striata (white striped) and so on. The remaining mutants were: early, irregular ear, slender (narrow leaf), dwarf, shrunk, etc. These mutants behaved like simple Mendelian recessives. The virescent mutants with partly green leaves, virido-albina and basi-viridis, mostly died out during the winter in the field, but not in the greenhouse. Moreover, these mutants could recover completely and produce green leaves under the light of a fluorescent lamp. As to the nature of the mutants, the same types were often observed in both varieties, flavescens and vulgare, showing a pronounced parallelism. But var. flavescens showed always a higher tolerance to X-rays than var. vulgare. |