Somatic cell cytology of the chromosome-eliminating, intergeneric hybrid Hordeum vulgare × Psathyrostachys fragilis

Abstract

In the hybrid Hordeum vulgare × Psathyrostachys fragilis the two genomes were differentiated (i) by length, the P. fragilis chromosomes being 31% longer than the H. vulgare chromosomes; (ii) by a difference in staining intensity of C-banded chromosomes (of possible use for exact localization of breakpoints), the H. vulgare chromosomes being the more heavily stained; (iii) by widely different C-banding patterns; and (iv) by the difference between N-banded H. vulgare and non-N-banded P. fragilis chromosomes. Only C-banding patterns identified each chromosome. Aneuploid cells had lost between one and five P. fragilis chromosomes. Loss of H. vulgare chromosomes is ascribed to squashing. No haploid H. vulgare cell was observed. The P. fragilis chromosomes were characterized by diminished centric constrictions, suppression of nucleolar constrictions, and nucleolus activity, i.e., differential amphiplasty, and generally a peripheral location on the metaphase plate. The same characteristics are normally observed in hybrids producing haploids H. vulgare, suggesting a common mechanism of chromosome elimination. Some cells had a side-by-side arrangement of genomes. The only effect of the hybrid condition on H. vulgare chromosomes was the formation of wider nucleolar constrictions and larger nucleolus organizer regions (NORs) than in parental H. vulgare, suggesting a compensational mechanism for nucleolus activity. The passage of H. vulgare chromosomes through the hybrid to the dihaploid did not influence chromosomal characteristics.Key words: Hordeum, Psathyrostachys, hybrids, elimination of chromosomes, banding.