Selective chromosomal elimination during haploid formation in barley following interspecific hybridization

Abstract

Cytological observations were made on embryo and endosperm tissues with different genome combinations that were produced by crossing the diploid and tetraploid cytotypes of Hordeum vulgare and H. bulbosum. The high frequency of barley haploids results from hybridization followed by the selective elimination of bulbosum chromosomes during the early development of embryos which initially contained a ratio of 1 vulgare to 1 bulbosum genomes. Elimination is gradual as indicated by the increase in the percentage of cells with the gametic chromosome number. However, the balance between genetic factors of the two parents appears to regulate the stability or elimination of chromosomes. Triploid embryos containing 1 vulgare to 2 bulbosum genomes are relatively stable. The most stable endosperm tissues examined had a ratio of 1 vulgare to 4 bulbosum genomes. Evidence of genetic control in both the vulgare and bulbosum chromosomes and their interaction is discussed. As has been suggested by Lange (1971) and also found in mammalian somatic cell hybrids, the most probable basis for selective chromosome elimination relates to mitotic rhythm and the duration of cell cycle phases.