Intergeneric Hybridization in Cichorieae, IX. Considerations on cytological and morphological features of F4 individuals of Paraixeris denticulate× Crepidiastrum platyphyllum with special reference to fertility
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1. Many F4 individuals of Paraixeris denticulata×Crepidiastrum platyphyllum were studied both morphologically and cytologically with special reference to their fertility.2. In many individuals the somatic chromosome number was 10. Only three had 11 chromosomes. The mechanism of preservation of the chromosome number was supposed to be well equipped.3. In the root-tips of four individuals, polyploid cells were observed beside the diploid ones. The tendency of chromosome doubling in heterozygocity seems not to be unusual.4. In many individuals new types of chromosomes were observed. This seems to be a similar phenomenon to the novation of Navashin, and seems to be caused by semihomologous crossing-over.5. In the meiotic division some individuals had only bivalents. But in the others multivalents or prematurely separating bivalents were observed in abundance. The forms and the components of multivalents were quite variable. In general more multivalents were observed in the earlier diakinesis than in the metaphase. From the observations of meiosis the following conclusions have been drawn.a) Winge's hypothesis of systematic importance of polymery may be applied also to the explanation of chromosome pairing.b) A hypothesis of residual affinity in pairing advanced by the present author explains adequately the various configurations observed.c) The secondary association may be a manifestation of residual affinity.6. There were little correlation between the pollen fertility and the rate of achene setting (r=0.20). The low pollen fertility was correlated with the multivalents and the low rate of achene setting with the prematurely separating bivalents. It was supposed that the mode of meiosis is different in male and in female, and that the pairing power is a little stronger in female.7. The fertility was much restored in F4 in spite of an increase of meiotic irregularities. This seems to be caused mainly by the restoration of cytoplasm-nucleus relations. It was suggested that the alteration of cytoplasm in accordance with the foreign nucleus will be taken place gradually both in somatic and germ cells.8. The inclination of F4 population to the type of Paraixeris parent was supposed to be the consequence of selection pressure of the cultural conditions. It is remarkable that new intermediate forms with higher fertilities have appeared.
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関連論文
- Intergeneric Hybridization in Cichorieae, IX. Considerations on cytological and morphological features of F4 individuals of Paraixeris denticulate× Crepidiastrum platyphyllum with special reference to fertility
- Intergeneric Hybridization in Cichorieae, VIII. Morphology and fertility of F4 individuals of Paraixeris derticulata×Crepidiastrum platyphyllum