Genomic alterations in the interspecific hybrid Helianthus annuus x Helianthus tuberosus

The genome of a Helianthus annuus (2n = 34) x Helianthus tuberosus (2n = 10 2) hybrid was studied at cytological, biochemical and molecular levels and compared to those of the parental species. Cytophotometric analyses showed that the hybrid has a 4C DNA content higher than expected and with a larger variability than in the parents. This high variability is probably not rel ated to chromosome-number variations since the hybrid always had 2n = 68 ch romosomes. Moreover, hybrid interphase nuclei showed lower heterochromatin condensation than the parental ones. Thermal denaturation of genomic DNAs i ndicated that, quantitative variation of some DNA families occurred in the hybrids compared to parents. Finally, molecular analyses of DNAs restricted with different enzymes, after Southern blotting and hybridization with HR probes, showed restriction patterns in the hybrid different from those obse rved in parents. These results indicate that interspecific hybridization be tween H. annuus and H. tuberosus may determine quantitative variation of so me DNA families and differential DNA methylations that probably modify the nuclear structure. These phenomena are probable responses to a "genomic sho ck" following the interspecific cross.