| Material and Methods Triticum aestivum cv. Chinese Spring (CS), the CS mutant ph1 and CS nulli-5B-tetra-5A line (AABBDD, 2n = 42) were used as the female parent in crosses with tetraploid wheat species T. timopheevii and T. militinae (AAGG, 2 n = 28). Spikes of hybrid F1 plants were fixed in Newcomer's fluid and anthers were squashed in 2% acetocarmine. PMCs were scored for the presence of uni-, bi- and multivalents. Results and Discussion The cytological data obtained from meiotic studies of F1 hybrids CS x T. timopheevii and CS x T. militinae showed that both of these hybrids exhibited substantially the same degree of meiotic irregularities with the mean number of bivalents 7.2 and 6.4, and multivalents, 0.63 and 0.25, respectively, per cell (Table 1). It is supposed that the chromosomes of the A genome of T.aestivum as well as of T. timopheevii and T. militinae took part in bivalent formation whereas the chromosomes of the B genome and the D genome of T. aestivum and the G genome of T. timopheevii and T. militinae remained in univalent condition or partially included in multivalents associations. When mutant ph1 and CS nulli-5B-tetra-5A line were used in the crosses the rate of homoeologous pairing in F1 hybrids increased significantly. In F1 hybrid plants CS mutant ph1 x T.timopheevii the mean numbers of bivalents and multivalents per cell were 8.3 and 1.1, respectively, and the percentage of PMCs with multivalents (tri-, quadri- and pentavalents) was rather high, 70.7 (Table 2). In F1 hybrids CS nulli-5B-tetra-5A x T. militinae and CS mutant ph1 x T. militinae the mean numbers of bivalents per cell were 8.4 and 8.7, multivalents, 0.68 and 0.85, and chiasmata, 13.3 and 13.2, respectively (Table 1). The percentage of PMCs with multivalents in these hybrids was equal to 52 and 61. It must be noted that in hybrids where CS nulli-5B-tetra-5A line and CS mutant ph1 were used as female parents the average number of bivalents in some PMCs reached 14 (Table 2). This fact suggested a possibility of pairing the homoeologous chromosomes of the G genome of tetraploids and the B genome of common wheat. |
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