THE ALLOCATION OF THE CHROMOSOMES OF TRITICUM AESTIVUM TO THE A AND B GENOMES AND EVIDENCE ON GENOME STRUCTURE

Abstract

Lines of Triticum aestivum Chinese Spring (2n = 6x = 42) ditelocentric for chromosome I-XTV were pollinated by Triticum thaoudar (2n = 14). The behaviour of the marked telocentrlc chromosomes was scored in the 14 distinct AABD hybrids obtained from these pollinations. In 7 hybrids the telocentrics were paired in from 48 to 70% of cells, so that the chromosomes marked by the telocentrics could be assigned to the A genome. In 7 other hybrids the telocentrics did not pair, or did so in not more than 2% of cells, so that the marked chromosomes could be assigned to the B genome. The earlier classification of Okamoto (1962) was confirmed in assigning chromosomes IV, VI, IX, XI, XII and XIV to the A genome and chromosomes I, III, V, VII, VIII and X to the B genome. In contrast to the earlier classification chromosome II is shown unequivocally to be in the A genome and chromosome XIII in the B genome. It is suggested that the designations of wheat chromosomes, indicating the homologous group and genome to which each belongs, should be retained. To avoid confusion it is further suggested that the reclassified chromosomes should be designated 2A(II) and 2B(XHI). The trivalents occurring in the T aestivum XT thaoudar hybrids are shown to represent interchanges between A and B genome chromosomes in T aestivum. The interchanges must have taken places at the tetraploid level and the frequent participation of chromosomes 2A(H) and 3A in trivalents suggest that these were 2 of the chromosomes concerned.