Response of inbred and hybrid maize seed to gamma radiation and fission neutrons and its relationship to nuclear volume

Measurements have been made of dose-response curves and relative biological effectiveness (RBE) for seedling growth reduction following seed irradiation of four inbreds, three single-cross hybrids, and one double-cross hybrid of maize with γ-radiation and fission neutrons. Also of primary interest was the relationship of response differences to nuclear volume. Caryopses (seeds) were adjusted to a water content of 13 to 14% prior to irradiation. Nuclear volumes were determined from nuclei in cells of the apical meristem. The inbred T232 was approximately 3 and 1.5 to 2 times more sensitive to γ-radiation and fission neutrons, respectively, than the other inbreds and hybrids. Except for T232, the D50 for γ-radiation was 35 to 40 krads. The response to fission neutrons was more variable; D50 s ranged from 0.79 krads for T232 to 1.79 krads for the double cross hybrid. This resulted in differences in neutron RBE, which ranged from 17.5 for T232 to 35.6 for the inbred T220. There was no consistent relationship between response to either kind of radiation and nuclear volume. (author)