Significance of Embryo Differentiation in Barley Interspecific Hybridization and Haploid Formation

Abstract

Reciprocal crosses between cultivated barley Hordeum vulgare (2x) and H. bulbosum (2x) results in haploids of H. vulgare (1) through selective elimination of bulbosum chromosomes from hybrid embryos (2, 3). In the hybrid plants that do not undergo elimination, chromosome instability exists but the extent of instability varies with the genome balance (ratio) of the original cross (4–7). The genome balance phenomenon is under the control of genetic factors located on chromosomes 2 and 3 of vulgare (8 – 10) whose dose ratio to bulbosum chromosomes is critical to the elimination process (2). The phenomenon of selective chromosome elimination leading to haploid formation is widespread among Hordeum interspecific hybrids (11 – 15) and intergeneric crosses involving H. bulbosum or H. vulgare (16 – 19). The evidence indicates that Hordeum species differ in their ability to eliminate, and the elimination is dependent on the ratio of the parental genomes in any cross combination. These findings in Hordeum interspecific hybrids led to the proposal of a hierarchy of species in dominance in selective chromosomal elimination (20).