Genetic effect of ionizing radiation in Einkorn wheat

Seiji MATSUMURA and Taro FUJII

National Institute of Genetics, Misima, Japan

Dormant seeds of Triticum monococcum var. flavescens were exposed to X-rays, gamma-rays and fast neutrons.

X-rays of different wave lengths at the same dosage (10kr), and intensity (82 r/min) were used with different filters; also the effect of gamma-radiation by Co⁶⁰ was examined for comparison. The thickness of the filter was adjusted inverse proportion to the wave length; that is, at 100 KVP a filter of 2 mm Al, and at 180 KVP one of 0.8mm Cu+ 1.5mm Al was inserted into MATSUDA's Type KXC-17 apparatus. At 50 KVP and 20 KVP, irradiation was applied by two other types, Modified Type KR-75 and Type TX-20 (Grenz-rays) without filter, respectively. The data are shown in the following table.

There was no striking difference between hard and soft X-radiation, in so far as the germination of seeds is concerned, but the growth of seedlings showed a slight delay with the decrease of wave length. The higher the dosage of gamma-rays or neutrons, the lower was the germination rate of irradiated seeds, and the more delayed were the germination of seeds and growth of seedlings. It was shown, in terms of growth inhibition of the seedlings, that neutrons with a high specific ionization more uniformly affect the irradiated seeds than X- and gamma-radiations with a low specific ionization.

The mean single-spike fertility of X-rayed plants generally decreased with the decrease of wave length. This relation is in good accord with that between the growth of seedlings and wave length. Also, the relation between the rate of induced sterility and wave length coincides roughly with the relation between the frequency of chromosome aberrations or chlorophyll mutations and wave length. But at 20 KVP the aberration frequency was unexpectedly high, while at 50 KVP it was too low.

It was also ascertained, as expected, that mean fertility decreased with decreasing germination rate accompanied by weaker growth of seedlings, and the chromosome aberrations increased in proportion to the dosage of gamma-rays and neutrons. Concerning the frequency of gene mutations in X₂, the head progenies which did not germinate at all, must be added to the chlorophyll mutations.

(Received May 20, 1958)