日本産ヨメナ属における種の分化の細胞学的, 形態学的および地理学的研究 III.

オオユウガギク Kalimeris incisa

抄録

1. Kalimeris incisa DC. of the Compositae occurs in Siberia, Manchuria, Northern China, Korea and the western part of Japan. The results of cytological investigations on records indicate that K. incisa is an octoploid species with 2n=72, but very little has been known about the properties of its populations. The present paper reports the results of morphological and cytological studies on a local population of the species found in the vicinity of Hiroshima, Japan.
2. A sample of 72 clones were taken from the population and grown in a uniform garden. Considerable morphological variation was recognized among those clones. The variation was so extensive that extreme variants were hardly identified as the species by gross external morphology alone.
3. Chromosome number was counted in all of the 72 clones, revealing that they were either octoploids with 2n=72 or aneuploids with 2n=70, 71, 73 or 74. Although the variation in chromosome number was limited to a narrow range of 2n=72±2, the aneuploids were found at a high frequency of 29.2 per cent. The majority of these aneuploids were with 2n=71.
4. Observations of karyotype were made at somatic metaphase and prometaphase. By the observations at prometaphase, the structural characteristics of the chromosomes of K. incisa were made clear to some extent. The largest and larger 8 of the 72 somatic chrosomes were satellited ones, and closely similar to each other in shape, size and structural characteristics. Among the other chromosomes the largest and larger 8 with subterminal constrictions were, again, closely similar to each other in morphological and structural characteristics.
5. Meiosis was observed in 10 clones with 2n=72. Forming 36_II in the large majority of PMCs, meiosis was almost regular in those clones. A configuration with 1_IV+ 34_II also appeared in each of the clones, although its frequency was much lower than that of 36_II.
6. The results of the present investigation suggest that in K. incisa the individual clones that compose a local population are cytologically fairly constant as octoploids, but an enormous genetic variability is present among those clones. Since there is some indication that the formation of hybrid swarms between K. incisa and some other species is not a rare event, the possibility exists that the spontaneous intercrossing has contributed to the genetic variability of K. incisa, leaving little recognizable trace upon its cytological characteristics.