Molecular cytogenetic characterization of parental genomes in the partial amphidiploid Triticum aestivum x Thinopyrum ponticum

The wheat line PF 839197 and six hybrid derivatives from a cross between PF 839197 and Thinopyrum ponticum were cytologically characterized by fluorescent in situ hybridization (FISH). Probes for the 5S and 45S rDNA genes (pTa794 and pTa71, respectively), a highly repetitive rye sequence (pSc119.2), the synthetic oligonucleotide (AAG)5, and total genomic DNA from Th. ponticum and rye were used. In the wheat line, a 1RS.1BL translocation was revealed by the labeling patterns produced with pSc119.2 and (AAG)5, and confirmed by genomic in situ hybridization (GISH) using rye genomic DNA as a probe. Analyses of partial amphiploids confirmed previous results indicating mitotic instability, with a tendency to stabilize at 2n = 42 or 56. GISH with Th. ponticum genomic DNA showed that in one hybrid derivative, with lower chromosome numbers (2n = 42-45), chromosomes were not labeled, whereas in the hybrids with 2n = 48-56 up to 14 chromosomes were labeled. These data suggest that the original chromosome set of these hybrids was 2n = 56, and that chromosomes from both genomes were lost by mitotic instability. FISH using the rDNA probes and GISH with Thinopyrum genomic DNA suggested that cells with 2n = 56 contained an entire wheat genome plus two monoploid chromosome sets of Th. ponticum