STABILIZATION OF TETRAPLOID TRITICALE WITH CHROMOSOMES FROM TRITICUM-AESTIVUM (ABD)(ABD)RR (2N=28)

F1 hybrids with the genome constitution ABDERR (2n = 6x = 42) or ABDE( AB)RR (2n = 7x = 49), selected from crosses between either an octoploi d Triticum aestivum/Thinopyrum elongatum amphiploid and tetraploid Sec ale cereale (AABBDDEE x RRRR) or autoallo-hexaploid triticale [AABBDDE E x (AB)(AB)RRRR], were backcrossed to tetraploid triticale (AB)(AB)RR and selfed for six generations. Thirty-three different tetraploid F6 progenies were karyotyped using C-banding. The aneuploidy frequency wa s 6.6% with 4.0% hypoploids and 2.6% hyperploids. Among 71 plants with 28 chromosomes, 53.5% had a stabilized karyotype while 46.5% were uns tabilized with at least one homoeologous group segregating for A-, B-, or D-genome chromosomes. The stabilized plants represent 19 different tetraploid karyotypes with six of them not containing any detectable D-genome chromosomes from T aestivum or E-genome chromosome from Th. e longatum. Thirteen lines were (ABD)(ABD)RR tetraploids with one-to-thr ee disomic substitutions of D-genome chromosomes for A- or B-genome ch romosomes. No disomic substitution of E-genome chromosomes was identif ied. On average 0.58 D substitutions per line were determined. Of the seven D-genome chromosomes only four, 1D, 2D, 5D, and 7D, were present in their disomic state. In unstabilized karyotypes, chromosomes 3D, 4 D, and 6D were present in their monosomic state. Among all 30 viable p lants (42.3%), the order of decreasing frequency of D-genome chromosom es was 5D (25.0%), 1 D (20.0%), 2D (10.0%), 6D (5.0%), and 3D (1.7%). Plants with 4D and 7D chromosomes were not viable. An increase in the number of D-genome chromosomes in the (ABD) genome is associated with a decrease in viability and fertility. Minor differences in the C-band ing of chromosomes in homoeologous groups 1, 5, and 6 indicate the pos sibility of translocations between A-, B-, D-, and E-genome chromosome s. Evolutionary and breeding aspects of tetraploid triticale with mixe d genomes are discussed.