Early evolution of the chromosomal structure of Triticum turgidum–Aegilops ovata amphiploids carrying and lacking the Ph1 gene

After two selfing generations of two different Triticum turgidum –Aegilops ovata amphiploids carrying the Ph1 gene, or lacking it (ph1c mutant), karyotypes of their offspring were scored by GISH (genomic in situ hybridization). On average, the chromosome number was lower than expected (56 chromosomes) on the basis of the parental constitutions (T. turgidum, AABB, 2n=4x=28; Ae. ovata, M^oM^oU^oU^o, 2n=4x=28). The lost chromosomes belonged to the wild Aegilops species. The two families differed greatly by their number of intergenomic translocations, also detected by GISH. The ph1c family showed nine translocations over 12 plants while only one translocation was observed in the Ph1 family. All exchanges involved either the M^o and U^o chromosomes or the M^o and wheat chromosomes, the size of the exchanged segment ranging from 3% to 36% of the total chromosome length. The results suggest an epistatic effect of the ph1c deletion over the genetic diploidizing system that operates in Ae. ovata since translocated chromosomes are most-likely derived from homoeologous recombination. The potential of these results for wheat breeding programmes is also considered. Received: 28 November 2000 / Accepted: 20 March 2001