Pairing affinities of the B- and G-genome chromosomes of polyploid wheats with those of Aegilops speltoides

Chromosome pairing at metaphase I was studied in different interspecific hy brids involving Aegilops speltoides (SS) and polyploid wheats Triticum timo pheevii (A(t)A(t)GG), T. turgidum (AABB), and T. aestivum (AABBDD) to study the relationships between the S, G, and B genomes. Individual chromosomes and their arms were identified by means of C-banding. Pairing between chrom osomes of the G and S genomes in T. timopheevii X Ae. speltoides (A(t)GS) h ybrids reached a frequency much higher than pairing between chromosomes of the B and S genomes in T. turgidum X Ae. speltoides (ABS) hybrids and T. ae stivum X Ae. speltoides (ABDS) hybrids, and pairing between B- and G-genome chromosomes in T. turgidum X T. timopheevii (AA(t)BG) hybrids or T. aestiv um X T. timopheevii (AA(t)BGD) hybrids. These results support a higher degr ee of closeness of the G and S genomes to each other than to the B genome. Such relationships are consistent with independent origins of tetraploid wh eats T. turgidum and T. timopheevii and with a more recent formation of the timopheevi lineage.