Cytological evidence bearing on the origin of the B genome in polyploid wheats

Abstract

To help elucidate the origin of the B genome in polyploid wheats, karyotypes of Triticum turgidum, Triticum monoccum, and all six purported B genome donors were compared. The analysis utilized a common cytological procedure that employed the most advanced equipment for the measurement of chromosome lengths at metaphase in root tip cells. A comparison of the karyotypes of T. turgidum and T. monococcum permitted the identification of B genome chromosomes of T. turgidum. These consist of two SAT pairs, one ST pair, three SM pairs, and one M pair of homologues. Comparisons of the chromosomes of the B genome of T. turgidum with the karyotypes of the six putative B genome donors showed that only the karyotype of Aegilops searsii was similar to the one deduced for the donor of the B genome in T. turgidum, suggesting that Ae. searsii is, therefore, the most likely donor of the B genome to the polyploid wheats. Support for this conclusion has been derived from geographic, DNA-hybridization, karyotype, morphological, and protein data reported since 1977. Reasons why the B genome donor has not been unequivocally identified are discussed.Key words: phylogeny, karyotypes, Triticum turgidum, Triticum monococcum, B genome, B genome donors.

High molecular weight glutenin subunit variation in the Sitopsis section of Aegilops. Implications for the origin of the B genome of wheat

“…6). Similar conclusions have been reached by Kerby and Kuspira (1988) from karyotypic studies, and by Natarajan and Sarma (1974) from comparisions of chromosome banding patterns.…”

“…searsii is the probable donor of the B genome since it is the only species in the Sitopsis section that has a sympatric distribution with both T. turgidurn and T. monococcum, and its satellite chromosomes show the same morphology as that of chromosomes I B and 6B of T. aestivum (Feldman, 1978). The karyotypic analysis carried out by Kerby and Kuspira (1988) seems to indicate the same conclusions. Ae.…”

“…Ae. sharonensis does not show the same karyotypic characteristics of the B genome (Kerby and Kuspira, 1988); however, Natarajan and Sarma (1974) indicated that the distribution of C-hetrochromatin in the chromosomes of Ae. sharonensis is very similar to that observed for chromosomes of the B genome, whereas Ae.…”

“…Although it is accepted that A and D genomes are derived from those of T monococcum and Ae. squarrosa respectively, evidence about the origin of the B genome of T turgidum and T. aestivum is still contradictory (see Kerby and Kuspira, 1988). …”

The extent and structure of genetic variation in species of the Sitopsis group of Aegilops

“…Vakhitov & Gimalov (1988) compared the 5S ribosomal RNA and Kerby & Kuspira (1988), using cytogenetic evidence, concluded that the five species were more or less equally related to one another. Yen & Kimber (1990) All five species were found to be primarily autogamous.…”