| Radiation effects of fast and thermal neutrons on wheat
: II. Relation of ploidy to chromosome aberrations M. NEZU National Institute of Genetics, Misima, Japan Meiotic irregularities induced by various irradiations were compared in tetra- and hexaploid wheats. The experimental data are shown in Tables 3 and 4. Chromosome aberrations induced by thermal neutrons operated by JRR-1 were mostly univalents and reciprocal translocations ((4) and (6)). Univalents and (6) were more prominent in 6x species than in 4x species. Average number of breakages per cell increased non-linearly with the increase of dosage, when a univalent was counted as one, (4) as two and (6) as three breaks. The number of breaks in 6x was about 3 times as high as in 4x species. No increase of breaks was found between two treatments, namely, (II) and (III) in both species. The number of breaks obtained by these treatments was comparable to that obtained by X- or gamma-rays of 10 kr subjected in ORNL. Seed fertility decreased with the increasing dosage in both 4x and 6x. The 6x was slightly more susceptible than 4x in this respect. The plants irradiated at more than 2.5 krad of fast neutron in ORNL did not grow. Meiotic irregularities could be examined only in plants irradiated at 2.5 krad. All chromosome configurations in 4x species were easily analyzed. The number of breaks observed was 4.47 per cell, which was about twice as much as at X-irradiation of 20 kr. In 6x species, a few cells had one complicated multivalent and many fragments which made an estimation of the number of breakages difficult. Estimated only from clear aberrations it was 5.26 per cell. This estimation might be somewhat too low. Both X- and gamma-irradiations at 10 and 20 kr caused breakages in 6x species about 3 times as many as in 4x species. X-irradiation produced breakages about 1.5 times as many as gamma-irradiation at 10 and 20 kr of 4x and 6x. There was no difference between sensitivities of 4x and 6x species in regard to X- and gamma-irradiation effects on fertility. |