Effects of acute gamma irradiation in growing barley plots

In 1961 and 1962 two sets of experiments were initiated with acute irradiation of the 2‐row barley variety Foma grown in the Bogesund gamma field. Sector‐shaped plots were treated during 24 hours, one at a time, at ontogenetic stages defined as tillering (in 1962 early and late tillering), meiosis, and spike emergence. The most profound effects in the year of treatment (γ 1 ) were achieved after irradiation at meiosis. The comparatively small effects of treatments at tillering were ascribed to counterselection. As a consequence of this selection the yield of mutations per unit of irradiation decreased by increasing dosage. The irradiations at meiosis yielded comparatively many mutants, most of them affecting seed set ability. The mutation yield per unit of radiation seems to decrease by increased doses, at least for the treatments where some material survived the irradiation. In the material irradiated at spike emergence, most mutations, too, were those affecting fertility but not to the same extent as after treatments of meiosis. The mutation yield per radiation unit did not decrease in the same way as for the tillering and meiosis treatments. Comparisons between the ontogenetic stages studied showed that the spike emergence stage is the stage to be preferred from a methodological and practical point of view. This proposal is based on the findings (i) that the selection against induced changes was less pronounced than in the tillering and meiosis treatments, and (ii) that the relative proportion of mutations not reducing fertility was greater than in the material irradiated at meiosis.