title: Chromosome pairing relationships among the A, B, and D genomes of bread wheat.
abstract: Chromosome pairing and chiasma frequency were studied in bread wheat euhaploids (2n = 3x = 21; ABD genomes) with and without the major pairing regulatorPh1. This constitutes the first report of chromosome pairing relationships among the A, B, and D genomes of wheat without the influence of an alien genome. AllPh1 euhaploids had very little pairing, with 0.62-1.05 rod bivalents per cell; ring bivalents were virtually absent and mean arm-binding frequency (c) values ranged from 0.050 to 0.086. In contrast, theph1b euhaploids had extensive homoeologous pairing, with chiasma frequency 7.5-11.6 times higher than that in thePh1 euhaploids. They had 0.53-1.16 trivalents, 1.53-1.74 ring bivalents, and 2.90-3.57 rod bivalents, withc from 0.580 to 0.629. N-banding of meiotic chromosomes showed strongly preferential pairing between chromosomes of the A and D genomes; 80% of the pairing was between these genomes, especially in the presence of theph1b allele. The application of mathematical models to unmarked chromosomes also supported a 2∶1 genomic structure of theph1b euhaploids. Numerical modeling suggested that about 80% of the metaphase I association was between the two most related genomes in the presence ofph1b, but that pairing under Ph1 was considerably more random. The data demonstrate that the A and D genomes are much more closely related to each other than either is to B. These results may have phylogenetic significance and hence breeding implications.
authors.affiliation: USDA-ARS, Forage and Range Research Laboratory, Utah State University, 84322-6300, Logan, UT, USA.
authors.forename: P P
authors.initials: PP
authors.lastname: Jauhar
authors.forename: O
authors.initials: O
authors.lastname: Riera-Lizarazu
authors.forename: W G
authors.initials: WG
authors.lastname: Dewey
authors.forename: B S
authors.initials: BS
authors.lastname: Gill
authors.forename: C F
authors.initials: CF
authors.lastname: Crane
authors.forename: J H
authors.initials: JH
authors.lastname: Bennett