Introduction of D-genome chromosomes from Aegilops squarrosa L. into tetraploid triticale (AB)(AB)RR (2n=28).

Tetraploid triticale with the genome constitution (ABD) (ABD)RR (2n=4x=28) selected from the progenies of DDRR x (AB)(AB)RR hybrids (D(AB)RR) were karyotyped using C-banding. The aneuploidy frequency was 10.7% with 4.4% hypoploids and 6.3% hyperploids in the F5. Among 67 plants having 28 chromosomes, 41.8% had a stabilized karyotype, while 58.2% were unstabilized with at least one homoeologous group segregating for A-, B- or D-genome chromosomes. The stabilized plants represented ten different karyotypes that contained one to five disome substitutions of D-genome chromosomes for A- or B-genome chromosomes. Two (BD) (BD)RR tetraploids had no A-genome chromosomes. The average number of D substitutions was 3.0 per line. Of the seven substitutions possible only one, 4D(4B), was not present. In the progeny of plants selected for fertility a selection pressure acted against wheat chromosomes 1B, 3B, 4D and 7D. The most favoured chromosome constitution of the (ABD) mixed genome was 1D, 2A, 3D, 4B, 5B, 6A and 7B. Plants of that karyotype but with a heterologous pair of chromosomes 5B and 5D had the best seed set. Evolutionary and breeding aspects of tetraploid triticale are discussed.