| Effect of X-rays on fertility and mutation rate in
Einkorn wheat S. MATSUMURA and T. FUJII National Institute of Genetics, Misima, Japan Dormant seeds of Triticum monococcum were exposed to various kinds of X-rays with different dosages or wave lengths, without a filter. The frequencies of ears with chromosome aberrations in X1-plants and of head progenies with gene mutations in X2 increased with X-ray dosage (5,400-13,500r). It was also fairly certain that the shorter the wave length of X-rays, the higher not only the frequency, of chromosome aberrations, but also that of gene mutations (c.f. WIS No. 2). In all cases the frequencies of both aberrations and mutations were higher in var. vulgare than in var. flavescens. Thus, var. flavescens showed always higher tolerance to X-rays than var. vulgare (Tab. 1). There were some quantitative differences between the effect of various kinds of X-rays upon the fertility of single spike of X1-plants. Mean fertility of each spike in untreated plants was 82.67% and 53.22% in var. flavescens and var. vulgare tespectively and that of X-rayed, plants decreased generally in a linear relation to the increase of X-ray dosage. This relation is in good accord with the relation between the frequency of chromosome aberrations or gene mutations and X-ray dosage. Also, there is a marked difference between the fertility at 80 and 180 KVP. This relationship of sterility to wave length coincides roughly with the relation of aberration or mutation frequency to wave length (Tab. 1). In all cases the fertility was also markedly lower in var. vulgare than in var. flavescens. The former variety matures later than the latter. Therefore, the fertility of var. vulgare is sometimes low and variable, influenced by higher summer temperature. Even taking into consideration this unfavorable seasonal factor, the fertility of X-rayed plants is more heavily reduced in var. vulgare than in var, flavescens. This might be due to the above mentioned difference in tolerance between both varieties. |