德昌杉木和米德杉木的胞核学研究

KARYOLOGICAL STUDIES IN CUNNINCHAMIA UNICANALICULATA AND VAR.PYRAMIDALIS

对近年在我国四川凉山发现的德昌杉木及其变种米德杉木的染色体核型的观察结果表明,它们基本上是由4对长染色体和8对短染色体组成,核型公式分别为K（2n）=22=L8m+S12m+S2sm和K（2n）=22=L8m+S10m+S4sm,与杉木的B型核型相似,只有1-2对近中着丝点染色体和随体均在第四对染色体上。还测量了这两种杉木的染色体体积和测定了核内DNA的相对含量。最后对它们起源的可能的原因以及杉木属内几个分类群的亲缘关系和分类学处理提出了一些设想和建议。

Cunnighamia unicanaliculata D. Y. Wang et H. L. Liu and var. pyramidalis D. Y. Wang et H. L. Liu, two new taxa recently found in south-western Sichuan Province of China, have both a very restricted yet sympatric geographical distribution, including De-chang and Miyi districts. There is a debate as regards the specific status of C. unica-naliculata. A comparative karyological investigation, including chromosome numbers, karyotype analyses and measurements of nuclear volume and DNA contents, was undertaken in order to shed some light on the phylogenetic relationships between these taxa and C. lanceolata （Lamb.） Hook. The karyotype formulas of the above two taxa and C. lanceolata are as follows : C.unicanaliculata; K（2n） = 22 = L8m+ S12m + S2sm ; C. unicanaliculata var. pyramidalis: K（2n） = 22 = L8m + S10m+S4sm; C. lanceolata （Type A）: K（2n） = 22 = Lsm + S14m + S2sm ; C. lanceolata（Type B）: K（2n） = 22 = L8m +S14m. From the a.bove karyotypes, we have found that C. unicannliculata and var. pyrami-dalis, which are very similar to each other, are closely related to C. lanceolata （Type B）, but seem more strongly differentiated in the following respects: （1） the former possessing 1-2 pairs of chromosomes with submedian primary constrictions each, while the latter with all chromosomes possessing median primary constrictions; （2） the satellites of the former being always located on the 4th pair of chromosomes, whereas the position of satellites of the latter varyingwith geographical distribution, being usually on the 1st and 4th pairs of chromosomes; （3） B-chromosomes being present in the latter （predominantly in the geographical races of southwestern China） but not seen in the former; （4） the average chromosome volume of C. unicanaliculata var. pyramidalis being 623.44, while those of the four geographical races of C. lanceolata being 667.2-796.0; （5） the comparative DNA amount of C. unicanaliculata var. pyramidalis being 5.54, while those of the various geographical races of C. lanceolata being 6.20-7.67. Upon an overall comparison of the data with regard to karyology, geographical distribution, ecology, morphology and isoenzymie patterns of the taxa in question, we come to the following conclusions. Cunninghamia unicanaliculata and var. pyramidalis axe most likely taxa originated from natural populations of C. lanceolata. The extreme environmental conditions of the habitats are thought to have played an important role in the production of these two new taxa, An elevation of over 2000 meters and the periodical aridity of climate of the habitat, which differed remarkably from those of C. lanceolata, made possible the isolation of alternative populations, accompanied by selection for adaptation to extreme environments. But the differences between these two newly-found taxa and C. lanceolata are karyologically minor and morphologically quantitative and tend to display a more or less continuous variation pattern. It is, therefore, suggested that they are probably geographical races or ecotypes of C. lanceolata, and are not distinct enough from the latter to warrant specific status. It seems best to treat both C. unicanaliculata and var. pyramidalis as infraspecific catorories of C. lanceolata.