Chromosome structure of Triticum longissimum relative to wheat.

Homoeologous pairing at meiotic metaphase I was analyzed in T. longissimum x T. aestivum hybrids in order to reconfirm the homoeologous relationships of T. longissimum chromosomes to wheat. Hybrids between T. longissimum and 'Chinese Spring' carrying the Ph1 gene or theph1b mutation, which showed low and high pairing levels, respectively, were used. Chromosome arms associated at metaphase I were identified by C-banding. The homoeology of chromosomes 1S (l) , 2S (l) , 3S (l) , 5S (l) and 6S (l) to wheat group 1,2, 3, 5, and 6 chromosomes, respectively, was confirmed. Chromsome arms 4S (l) S and 7S (l) S showed normal homoeologous relationships to wheat. The 4S (l) L arm carries a translocated segment from 7S (l) L relative to wheat. The 7S (l) L arm seldom paired, likely because this arm lost a relatively long segment and received a very short segment in the interchange with 4S (l) L. Available data suggest that translocation 4S (l) L/7S (l) L arose in the evolution of T. longissimum, which implies that this species was not the donor of the B genome of wheat.