The Cytogenetics of Non-amphidiploid Derivatives of Wheat-Rye Hybrids

抄録

F₁ hybrids between wheat and rye are completely male-sterile and so nearly female-sterile that artificial backcrossing is nearly fruitless. With open pollination less than 0.02 per cent of the fully developed flowers set seed.
All F₁ eggs which functioned resulted from a process of restitution which was observed at both meiotic divisions of F₁ During the process both the loss and duplication of chromosomes may occur so that the number in functioning eggs may vary slightly above or below the somatic number 28 (21 wheat+7 rye), and the genic content may be quite variable.
The second generation feil into 3 fairly equal groups with approximately 28, 42, and 49 chromosomes respectively. Both the chromosome behaviour and the genetical characters indicate that the 28-chromosome group originated through parthenogenetic development of F₁ restituted eggs. In both respeets they are similar to F₁, with such exceptions as would be due to the loss or duplication of chromosomes at restitution. Their occurrence supports the theory that amphidiploids may be due to parthenogenetic development of restituted eggs followed by chromosome doubling.
Plants of the 42-chromosome group had only about 14 pairs at meiosis, exhibited characters of emmer wheats, and were very sterile. It is believed that they originated through the fertilization of restituted eggs by sperms from pure 14-chromosome (emmer) wheats. They had a genom from each of T. vulgare, an emmer, and rye.
Plants of the 49-chromosome group had about 21 pairs at meiosis, exhibited chiefly vulgare wheat characters, and were much more fertile. They originated through fertilization of restituted eggs by sperms from 21-chromosome wheat.
A prolonged effort was made to establish, among the descendants of the 49-chromosome group, lines with more than 21 pairs and with rye characters. Although a considerable number of plants with 22 or more pairs were identified, it was impossible to make the condition constant. Similarly, although different rye characters were retained for many generations by selection, it was impossible to secure true-breeding lines with rye characters. Characters somewhat resembling certain ones of rye were established in a few lines but were shown to be due to out-crossing to emmers during the early sterile generations.
No evidence could be found that individual rye chromosomes can be added permanently to the wheat complement, or substituted for wheat chromosomes, nor that by crossing-over or translocation composite wheat-rye chromosomes can be produced or at least can cause a visible effect.
Special features described and discussed are: chromosome doubiing in one-quarter of one Pollen sac without producing quadrivalents; secondary pairing; and a haploid plant.