Cytogenetic analysis of a spontaneous 5B/6B translocation in tetraploid wheat landraces from Ethiopia, and implications for breeding

Three tetraploid (2n = 4x = 28) wheat Triticum turgidum L. landrace morphot ypes(= genotypes) from Ethiopia were found to carry a variant karyotype dir ectly discernible under the microscope. This was possible because the rearr angement involved one of the satellited chromosomes. Giemsa C-banding revea led that the rearrangement resulted from a 5BS.6BS(5BL.6BL) centric recipro cal translocation. The: banding pattern on 5BL was polymorphic, suggesting that this translocation might have occurred more than once. There was littl e C-band polymorphism for the remaining chromosomes, except for 2A. As pure lines, all three morphotypes showed normal chromosome pairing at metaphase I (MI) in pollen mother cells (PMCs), indicating that they are genomically stable. Meiotic analyses of F-1 hybrids and F-2 segregates derived from cr osses with tester varieties clearly indicated that one of them (B-1-9) carr ied another translocation. However, we were not successful in detecting the chromosomes involved, presumably the interchanged segments did not include C-banding regions. By using T5BS.6BS, direct evidence for segregation dist ortion against translocation homozygotes in intervarietal hybrids was obtai ned. The distorted segregation was attributed to zygotic selection. No aneu ploid plants were obtained from the F-2 segregates. However, translocation heterozygotes resulting in unstable meiosis were abundant in the F-2 genera tion. The implications of the results in using the indigenous landraces in hybridization breeding are discussed.