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 hybrids involving Aegilops speltoides (SS) and polyploid wheats Triticum timopheevii (AtAtGG), 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 chromosomes of the G and S genomes in T. timopheevii x Ae. speltoides (AtGS) hybrids 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. aestivum x Ae. speltoides (ABDS) hybrids, and pairing between B- and G-genome chromosomes in T. turgidum x T. timopheevii (AAtBG) hybrids or T. aestivum x T. timopheevii (AAtBGD) hybrids. These results support a higher degree 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 wheats T. turgidum and T. timopheevii and with a more recent formation of the timopheevi lineage.