Chromosome elimination in Hordeum vulgare x H. bulbosum hybrids : 2. Chromosome behaviour in secondary hybrids.

The hybrid progeny from a stable amphidiploid of H. vulgare x H. bulbosum involving the cultivar 'Vada' and an unstable amphidiploid involving the cultivar 'Emir' were studied. The genotypes examined contained two genomes from 'Vada' or one from 'Vada' and one from 'Emir', with one or two genomes from H. bulbosum. Comparisons between the chromosome numbers in root-tips and anthers revealed that there was no chromosome elimination in most plants, whether there was one or two Vada genomes present. The one plant in which chromosome elimination was positively identified had 'Emir' as opposed to 'Vada' cytoplasm. It also had a high incidence of degraded or fragmented chromosomes in the PMCs. Differences in stability between a 27 chromosome plant and other hypotetraploids suggest that 'Vada' contains both elimination genes and elimination suppressor genes. Upon selfing, again irrespective of the number of 'Vada' genomes present, circa triploid hybrids gave rise to diploid H. vulgare offspring while hypotetraploids produced hybrid-like plants. These included diploids, triploids and tetraploids. There was evidence that suggested that H. vulgare as well as H. bulbosum chromosomes had been eliminated.