Effects of X- and gamma-radiations upon wheat seedlings and their modification due to temperature or polyploidy

S. MATSUMURA, T. FUJII and S. KONDO

National Institute of Genetics, Misima, Japan

Dormant seeds of Triticum monococcum were subjected to X- and gamma-ray treatments at dosages of 10 and 20 Kr. The germination rate of treated seeds and the growth of seedlings were compared for acute and chronic irradiation. In the former X- and gammar-irradiation was applied either immediately before sowing or the irradiated seeds were kept for 30 days in storage and in the latter gamma-irradiation lasted 54 days. In one experiment with acute irradiation one part of the treated seed were kept at room temperature (about 20C) and the remainder at low temperature (5C) for 30 days.

There was no marked difference in germination rate between untreated and treated seeds at 10 Kr, while the germination rate was reduced to 1/2-2/3 at 20 Kr. In the case of 30 day storage, gamma-rays inhibited the growth of seedlings more than X-rays, while the irradiation applied just before sowing showed the reverse relation. It was found further especially with gamma-rays that low temperature was more effective in inhibiting growth than room temperature. At 10 Kr, the acute gamma-irradiation was more effective in this respect than the chronic one. On the other hand, the reverse relation between acute and chronic gamma-irradiation was observed.

To examine the relation between the sensitivity to ionizing radiation and polyploidy, dormant seeds of Triticum monoccocum (2x), T. durum (4x) and T. vulgare (6x) were exposed to X- and gamma-rays at the dosage 10-40 Kr. In general, gamma-irradiation had a markedly stronger inhibiting effect upon seed germination and seedling growth than X-irradiation. 2x was most sensitive to X- and gamma-rays and 6x was most resistant. There was unexpectedly no significant difference between 4x and 6x.

(Received Nov. 6, 1957)