X-ray experiments on dormant seeds of six-rowed barley.

Abstract

In this expenment the vanety chosen was Sekitori Sai No.1, a six-rowed barley, now widely cultivated in Kanto area in Japan. Dormant seeds which had been stored under laboratory conditions since the previous harvest were used for irradiation. The seeds were placed in open petri dishes at about 9 cm. from target of a 60 kVp X-ray plant, run at 4 mA., where the dose rate was 235 r. per minute. After doses of 435 r. to 25, 000 r. were given, the seeds were sown in the field together with unirradiated seeds from the same sources. Contrary to expectation, even with higher X-ray doses maOrity of barley seeds produced plants up to maturity. The plant growth determined by measurements of the total height of the 18-day seedling after was sowing inhibited with the higher dose of X-rays. As regards the shape of the grbwth / dose curve, the X-rays gave a sigmoid curve (Fig. 1). The average spike fertility, as evidenced by seed set of the irradiated generation, decreased due to X-irradiation. The average spike fertility is the function of X-ray dose as illustrated by Fig. 2. Regression analysis indicated that relationship was linear. Three to five spikes were removed from each plant, and the seeds were sown for seedling mutation studies. The mutations observed resulted from chlorophyll deficiencies, and a linear relation between dose and frequency of mutations was obtained (Fig. 3). While at low doses the frequency of mutations per spike proge'ny and per dose unit was almost constant, at higher dcse there was a drop in the amount of effect produced per dose unit (Table 1). Also, in this experiment, the phenotypic effects, differed in response to varying doses, i.e., tlle mutation freqliency of viridis increased linearly with dose, while that of albilea showed a similar linear response to lower doses but somewhat decrement in the frequency of mutation at high doses. Most of the mutants were produced in the same relative frequencies as observed by earlier workers (Table 2).