THE FATE OF RECOMBINANT CHROMOSOMES AND GENOME INTERACTION IN NICOTIANA ASYMMETRIC SOMATIC HYBRIDS AND THEIR SEXUAL PROGENY

Genomic in-situ hybridization (GISH) was used to monitor the behaviour of parental genomes, and the fate of intergenomic chromosome transloc ations, through meiosis of plants regenerated from asymmetric somatic hybrids between Nicotiana sylvestris and N. plumbaginifolia. Meiotic p airing in the regenerants was exclusively between chromosomes or chrom osome segments derived from the same species. Translocation (recombina nt) chromosomes contained chromosome segments from both parental speci es, and were detected at all stages of meiosis. They occasionally pair ed with respectively homologous segments of N. sylvestris or N. plumba ginifolia chromosomes. Within hybrid nuclei, the meiotic division of N . plumbaginifolia lagged behind that of N. sylvestris. However, normal and recombinant chromosomes were eventually incorporated into dyads a nd tetrads, and the regenerants were partially pollen fertile. Recombi nant chromosomes were transmitted through either male or female gamete s, and were detected by GISH in sexual progeny obtained on selfing or backcrossing the regenerants to N. sylvestris. A new recombinant chrom osome in one plant of the first backcross generation provided evidence of further chromosome rearrangements occurring at, or following, meio sis in the original regenerant. This study demonstrates the stable inc orporation of chromosome segments from one parental genome of an asymm etric somatic hybrid into another, via intergenomic translocation, and reveals their transmission to subsequent sexual progeny.