Meiosis of intergeneric hybrids between polyploid species of Hordeum and Secale

Meiotic MI chromosome pairing was analyzed in a total of 34 intergeneric cross combinations between species of Hordeum L. (4x, 6x) and Secale L. (2x). By virtue of a pronounced difference in size between the chromosomes of Hordeum and Secale , the parental origin of the meiotic chromosomes could easily be determined. This offered an excellent opportunity to study the meiotic chromosome behaviour of the polyploid species of Hordeum. Some autosyndetic chromosome pairing was obtained in all hybrids. Hybrids involving the tetraploids H. secalinum and H. capense showed the lowest level of pairing. In general a somewhat higher level was found in hybrids involving H. brachyantherum (4x, 6x), H. jubatum (4x), H. lechleri (6x), H. procerum (6x), and H. arizonicum (6x). By far the highest level of pairing was obtained in hybrids involving H. depressum (4x), which suggests an autoploid origin of this species. When the level of autosyndetic pairing among the chromosomes of Hordeum in hybrid combinations with Secale was compared to the level reported in corresponding di‐ and trihaploids of Hordeum , the former level was generally found to be significantly higher. This is an indication of the existence of a genetically controlled meiotic regulation mechanism in the polyploid species of Hordeum , ensuring bivalent formation at the polyploid level, functional in the polyhaploids, but being less effective under the influence of the genome of Secale.