Studies in neutron mutagenesis in maize. --Effects of dose fractionation and cell moisture status on mutation induction.

Pollen grains of Bz strain of maize were exposed to 14 MeV neutrons with single or fractioated treatments, and pollinated on the recessive stock. Mutation frequency from Bz to bz was observed after harvest of F1 seeds. No clear difference in the mutation frequencies between single and fractionation series was observed. To investigate the effects of water content upon mutation frequency of neutron and gamma-rays, seeds heterozygous for the Yg2-gene were used. Moisture-stabilized (13%) seeds and seeds steeped in water for 24 hrs were exposed to neutrons or to gamma-rays, and mutation from Yg2 to yg2 was detected as color change green to yellow-green in the seedlings. In the gamma-ray treatments, the mutation frequency of wet seeds was about 1.5 times higher than that of corresponding lot of dry seeds. In the neutron treatment, on the other hand, no clear difference in frequency between wet and dry seeds was observed. It may be concluded that no change or no recovery in neutron-induced mutationwas observed not only in the fractionation treatment but also in the dry and wet seeds treatments.