Effects of seed moisture content, gamma rays, and unmoderated fission neutrons on various biological end-points in barley, Hordeum vulgare L. emend Lam

Seeds of the barley variety, Atlas 57, whose moisture content was equilibrated to 5.6, 7.4, 11.8 and 15.6 percent, were irradiated with gamma rays at 12, 24, 36, 48 and 60 kR and with fission neutrons at 190, 380, 570, 765 and 960 rads tissue equivalent in air. Seedling height, survival frequency, meiotic chromosome aberrations and seed fertility in the M₁ generation and the frequency of chlorophyll and viable mutations in the M₂ generation were studied. Varying the moisture content of the seeds modified the radiosensitivity following fission neutron as well as gamma irradiation, but in different ways. Considering mutation rate as the criterion, seeds with the highest moisture content showed maximum sensitivity following gamma rays, while seeds with the lowest moisture content were more sensitive to neutron irradiation. Varying the seed moisture content caused the mutation rate as well as mutation spectrum to vary with both kinds of radiations used. Neutrons induced a higher frequency and a wider spectrum of mutations than did gamma rays. The higher frequency of mutations observed with neutrons has been attributed to damage of more primordial cells of the embryo. Though all the biological end-points studied did not show the same kind of response, certain interesting correlations were observed between different criteria studied. High positive correlations were observed between seedling height and survival, chromosomal aberrations and mutation rate, chlorophyll mutation rate and viable mutation rate, and mutation rate and mutation spectrum. Speculated reasons for the differential radiosensitivity with varying preirradiation seed moisture contents, kinds of radiations used and usefulness of equilibration of seed moisture content in mutation breeding programs were discussed.