Abstract
Genome constitutions of Thinopyrum junceiforme (A. Löve and D. Löve) A. Löve (2n = 4x = 28) and T. sartorii (Boiss. &Heldr.) A. Löve (2n = 4x = 28) were determined by studying (i) meiotic pairing patterns in hybrids involving the two species and other pertinent hybrids; (ii) mitotic chromosome karyotypes based on length, arm ratio, and satellites; and (iii) C-banding patterns. New hybrids synthesized and reported are T. sartorii × T. bessarabicum (2n = 3x = 21), T. sartorii × (T. bessarabicum × T. elongatum) amphidiploid (2n = 4x = 28), and the reciprocal of the latter. Mean meiotic pairing in the triploid hybrid and the two tetraploid hybrids were 3.83 I + 3.92 II + 3.11 III, 0.931 + 7.46 II + 0.62 III + 2.44 IV + 0.07 V + 0.03 VI, and 3.41 I + 9.39 II + 0.74 III + 0.88 IV, respectively. Based on the chromosome pairing data, it can be concluded that T. junceiforme and T. sartorii have two versions (Jb and Je) of the J genome and behave like true allotetraploids owing to bivalentization. Karyotype analyses of the species and their hybrids with T. bessarabicum revealed minor structural differentiations of the genomes in the two species. Thinopyrum sartorii has one genome basically unchanged from the Jb genome of T. bessarabicum while another is a modified Je genome of T. elongatum. One genome of T. junceiforme is modified from Jb and the other is modified from Je. There are two pairs of large and one pair of small satellites in T. sartorii, but there are only one pair of each in T. junceiforme. Thinopyrum junceiforme is rich and T. sartorii is poor in interstitial C-bands for both sets of genomes. Thinopyrum sartorii has larger terminal C-bands on the Jb genome chromosomes than those of T. junceiforme. These organizational changes of chromosomes could not be detected by studying chromosome pairing alone. However, this study demonstrates that meiotic pairing is the first criterion for determining basic genome symbols. Other techniques, such as those involving chromosome banding, isozymes, and DNA probes, may then be used to detect differences in chromosome (or DNA) organization and gene expression.Key words: genome, hybrid, meiosis, karyotype, chromosome banding, speciation.
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