Radiological study of wheat monosomics, 3

As a means for studying the genetic similarities and dissimilarities of 21 wheat chromosomes, self-pollinated seeds of 21 monosomic strains of a common wheat Triticum aestivum cv. Chinese Spring were irradiated with γ-rays (0-60 kR), and their survival rate was observed about 30 days after sowing. Results were as follows: (1) Monosomic strains were, in general, much more sensitive to γ-rays than was the disomic. (2) The three monosomic strains of the same homoeologous group tended to show the same degree of sensitivity; group 2 was the most sensitive, followed by group 1,6, and 3,4 and 5. Group 7 was as resistant as the disomic. (3) In some homoeologous groups, a remarkable difference was noted among the three monosomic strains; groups 1,3,4 and 5. (4) The lowest dosage of γ-rays, at which an appreciable killing occurred, was: 35 kR in mono-5B; 40 kR in mono-2A, (probably 2B), 2D, 3A, 3A, 4A, 6A, and 6D; 45 kR in mono-1A, 1B, 1D, 4D, 5D, and 6B; and 50 kR in mono-3D, 4B, 5A, 7A, 7B, 7D, and the disomic. Functional differentiation of the homoeologous chromosomes took place at different rates in the different homoeologous groups. (5) The differential killing of the 21 monosomics and the disomic by γ-rays was, to some extent, correlated with the frequency of nullisomic, the average seed weight, the length of the monosomic chromosomes, and the survival rate of non-irradiated material. All these factors combined, however, explained only about 50% of the differences observed among the 22 strains. (author)