title: [Studies on the relationship of fertility and mode of chromosome pairing in tetraploid F1 species hybrids of rye (Secale cereale × Secale montanum) heterozygous for three translocated chromosomes].
abstract: 1. The practical purpose of the present investigation was to determine whether "preferential pairing" occurs in artificially induced tetraploid F1 species hybrids ofS. cereale andS. montanum which are heterozygous for three translocated chromosomes. Under these conditions chromosomes might form bivalents rather than the multivalent rings and chains usually found, resulting in a normal degree of fertility. 2. Several individuals of the tetraploidF 1 generation, heterozygous with respect to three translocated chromosomes, showed the expected percentages of quadrivalents always found in tetravalent rye, all other chromosome associations were bivalent (group 1 in table 1). The remaining individuals investigated also produced fewer multivalents than theoretically expected on the basis of the model proposed by Linnert (1962) and extended by us to include translocation figures composed of three translocated chromosomes. 3. It is to be assumed that in all of the plants investigated cytologically the quadrivalents were formed by the chromosomes not involved in the translocations. 4. Since the fertility of individuals with a strong tendency to form bivalents (group 1 in table 1) was no higher than that of plants producing a rather high percentage of multivalents, the rather high proportion of bivalents cannot be attributed to "preferential pairing" between chromosomes with increasing degrees of homology. Instead, it should probably be assumed that in the plants in question chiasma frequency was extremely low, so that heteromorphic bivalents instead multivalents were produced. 5. Proof of "preferential pairing" by cytological methods alone is rather difficult, because of the necessity to correctly distinguish the heteromorphic bivalents from the normal ones. It is discussed how use of the structural difference of chromosome VI ofS. montanum as compared to chromosome VI ofS. cereale which we detected recently, may serve to overcome this difficulty. 6. It appears that the goal of breeding a perennial, fully fertile, high-yielding rye hybrid may be achieved much more easily in diploids than in tetraploids, for in the tetraploid species hybrid success depends upon the selection not only of genotypes with high heritability for chiasma frequency but also for "zig-zag" distribution of the chromosomes involved in the formation of multivalents. In spite of our failure, a continued search for true "preferential pairing" may lead to its discover.
authors.affiliation: Max-Planck-Institut für Kulturpflanzenzüchtung, Hamburg, BRD.
authors.forename: R
authors.initials: R
authors.lastname: Reimann-Philipp
authors.forename: H
authors.initials: H
authors.lastname: Eichhorn-Rohde