| In (cer)-CS with one midget chromosome, estimated transmission
rate of the midget chromosome through female and male gametes was about
10% and 75%, respectively. The low transmission rate though the female must
be caused by elimination of the midget chromosome at meiosis of egg mother
cell as in wheat monosomics. The high transmission through the male must
be caused by the preferential fertilization of the pollen having midget
chromosome. In CS with one midget chromosome, however, transmission rate
was about 10% through both the gametes. The origin of the midget chromosome seems to be the rye chromosome of the initial amphidiploid, Secalotricum. In test crosses between (cer)-CS and Imperial rye disomic addition lines of CS, 79% of F1 seeds between (cer)-CS and 1R disomic addition line fully developed. In all cross combinations involving other rye chromosome addition lines, more than 75% of F1 seeds were shriveled. This indicates that chromosome 1R as well as the midget chromosome had the favorable effect on the endosperm development of (cer)-CS. Chromosome 1R had clear C-bands at the ends of both arms, while the midget chromosome had no band. These results indicate that the midget chromosome has to be derived from 1R by deleting the most part of both arms and retaining the centromere and the small region being responsible for the endosperm development. Since the interaction effect between the midget chromosome and the cereale cytoplasm is critical on the endosperm development of common wheat with cereale cytoplasm, screening of plants having this chromosome is easy in common wheat with cereale cytoplasm. Therefore, this chromosome can be used for genetical and breeding research on such as the endosperm formation in wheat and rye. This work was supported in part by the Grant-in-Aid for Special Project Research from the Japanese Ministry of Education, Science and Culture, Japan (No. 61117001). |
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