Chlorophyll-deficient mutation frequency in barley following continuous gamma irradiation over a wide range of exposures throughout the life cycle

Abstract

An experiment was conducted to test the influence of continuous γ-irradiation over a wide range of exposures throughout one life cycle on inducing chlorophyll-deficient mutations in barley ( Hordeum vulgare ). 200 seeds per treatment were planted at various distances from the radiation source. Treatments ranged from 0.17 R/day (16.5 R total exposure) to 23.2 R/day (2240 R total exposure). The plants were exposed 20 h per day from time of emergence until harvest (96 days) and the apical spikes harvested from each surviving plant. 20 seeds (at random) from each spike were removed and bulked with those from other spikes within the same treatment to make up the M 1 population. Seeds from non-irradiated plants were also included as a treatment. Up to 5 spikes were harvested from each M 1 plant, planted in greenhouse benches, and M 2 seedlings scored for chlorophyll-deficient mutants. M 1 plant survival and reduction in seed set were approximately the same regardless of the treatment. The frequency of mutations per 10 000 M 2 seedlings from 1.3 for the non-irradiated population to 4.3 for progeny of plants receiving 0.17 R/day. This frequency remained about the same through 1.45 R/day. At 3.17 R/day, the frequency increased to 7.0 and was 45.4 at 23.2 R/day. Although there appears to be a plateau and the low exposures, it is not possible to determine the exact shape of the dose response. A mathematical model with an equation of the form Y = Be cx2 and also a linear-linear model were used to summarize the data. The mutation spectrum from all treatments was 70.6% albina, 17.6% viridis and 11.7% others.