(go to KOMUGI Home) (go to WIS List) (go to NO.79 Contents)

Results and Discussion

Table 1 shows the frequencies of MI cells with different pairing configurations in 22 different monotelodisomic hybrids between Saitama 27 and CSDT lines.

Two multivalents plus one heteromorphic bivalent were observed in 1.6 and 1.4% cells of two hybrids involving CSDT 2DS and 5DL, respectively. This confirms that Saitama 27 had two independent reciprocal translocations relative to CS, and that one of them was of small segments.

Among the 22 kinds of hybrid, only those involving CSDT 3AS, 3AL and 7AL had shown a quadrivalent with telosome (t3'''') in 48.7,47.0 and 53.3% cells, respectively (Table 1, Fig. la). The remaining hybrids did not show t3'''' (Table 1). These indicate that chromosomes 3A and 7A were involved in one reciprocal translocation in Saitama 27.

In the hybrids of Saitama 27 with CSDT 3AS and 3AL, there were no significant differences in frequencies of MI cells with different configurations involving the telosome (chi2 = 5.97, df=4, 0.25>P>0.1) (Table 1). This suggests that the translocation between 3A and 7A involves large interchanged segments sufficient for chiasma formation. The C-banding patterns of the translocated chromosomes were compared with the standard ones in CS. Chromosome pairing and C-banding analysis suggest that the breakpoints in this translocation were within the centromeric regions. However, the arm combination of the translocated chromosomes could not be identified because 7AS and 7AL were not distinguished. Saitama 27 formed 1'''' in 26.0% of cells in the hybrid with Igachikugo Oregon having translocated chromosomes T3AS*7AL and 3AL*7AS (Ali et al. 1992, Nakata et al. 1993). This indicates that the reciprocal translocation between 3A and 7A in Saitama 27 differs in the interchanged arm combinations from that of Igachikugo Oregon. Thus, the translocated chromosomes in Saitama 27 are probably T3AS/7AS and T3AL/7AL (Fig.2).

In the hybrid involving CSDT 1AS, two cells having a configuration of 1''''+1'''+17''+ t' were observed (Fig. la). This indicates that chromosome 1A was involved in translocation of small segments. Though the hybrid with CSDT 3BL showed a configuration of 1'''' +1'''+16''+ 2'+ t' (Table 1), the involvement of 3B in this translocation is not certain due to the presence of two univalents. In this study, the counterpart in this translocation could not be identified because the size of the interchanged segment is too small to pair with its homologous telosome.

Saitama 27 formed hexavalent in the hybrid with Eshimashinriki (Ali et al. 1992). This implies that a common chromosome was involved in two different reciprocal translocations in both of the varieties. Chromosomes 3B, 4B, 6B and 7B were involved in two independent reciprocal translocations in Eshimashinriki (Ali et al.1994b). Thus, one of these four chromosomes could be involved in the translocation of small segments present in Saitama 27.

Saitama 27 was developed from a cross of the F1 hybrid between California and Soujukuakage with Hayakomugi (Fukunaga and Inagaki 1985). Soujukuakage had two translocations relative to CS, whereas Hayakomugi had not (Ali et al.1994a). This suggests that Saitama 27 might have inherited these translocations from Soujukuakage.

Meiotic instabilities and the occurrence of aneuploids were occasionally reported in the course of wheat breeding (Riley and Kimber 1961, Watanabe 1962, Worland and Law 1985, Suarez et al.1988). Watanabe (1962) reported that 37 of 207 Japanese varieties showed high frequencies (5-20%) of abnormal tetrad associated with the occurrence of high frequency of univalents at meiosis. The univalents of wheat chromosomes misdivide with high frequency. Sears (1954) showed that the frequencies of plants having telosome or isochromosome in the progenies of CS monosomics varied from 0.9% of 4D to 16.9% of 6A. Merker (1992) obtained 11 (1.98%) plants with T5B/5R in the selfed 575 progenies of monosomic 5B-5R substitution plants. These reports suggest that the centromeric translocation between 3A and 7A of Saitama 27 might be resulted from meiotic irregularities and centromeric misdivision-fusion of univalents.

<--Back | -->Next

(go to KOMUGI Home) (go to WIS List) (go to NO.79 Contents)