Cytological Study On Alnus Species In China

Alnus is the most primitive among the extant genera in Betulaceae. Because of the ability to symbiotically fix nitrogen, had attracted considerable attention from botanists all over the world. Since 1920s, the chromosome numbers have been counted for most species of Alnus distributed in Europe, North America, and Japan. However, there were few reports on the chromosome numbers and karyotype analyses of Alnus species in China. In the present study, 11 Alnus species, were cytologically carried out, including 10 distributed in China and A. pedula native to Japan. Hopefully it would provide the cytological data which is necessary to reveal the relationship among Alnus species, to reveal their origin and evolvement. Apart from demonstrating the optimal method for preparing mitotic chromosomes in Alnus, chromosome numbers of 11 species and karyotype analyses of 9 were given. The results were summarized as follows:1) Mint beverage water mixed with a little 8-hydroxyquinoline was regarded as the favorable pretreatment method of making good chromosomal specimens in Alnus. It is easier to operate, safer and cheaper compared with previous methods.2) There were three kinds of chromosome numbers of somatic cell in 11 Alnus species, respectively 2n=28,2n=56 and 2n=112.3) The chromosome numbers of A. sieboldiana and A. japonica are 2n=112. Karyotype formulas of the other nine Alnus species were showed, namely, K(2n)=56=30m+24sm+2st for A. ferdinandi-coburgii; K(2n)=56=38m+16sm+2M for A. cremastogyne; K(2n)= 56=28m+26sm+2st for A. nepalensis; K(2n)=56 =40m+14sm for A. lanata; K(2n)=56=52m+4sm for A. sibirica from Jilin province; K(2n)=28=24m+4sm for A. mandshurica; K(2n) =56=22m+32sm+2st for A. trabeculosa; K(2n)=56=44m+12sm for A. fomosana; K(2n)=28=20sm+6m+2st for A. pedula. The karyotypic type of A. ferdinandi-coburgii and A. sibirica from Jilin province belongs to 2A of stebbins' classification, and that of the other 8 Alnus species belongs to2B.4) The appliance of WDH in Alnus species was still immature and further exploration needs to be made mainly due to the influence of thick cytoplasm and the difficulty of coloration.5) The results suggested that obvious difference of chromosome number appeared among these Alnus species, even in the same species from different population, and spontaneous polyploidy might occur. Most domestic species have chromosome number 2n=56, except that A. sibirica is 2n=28. Combined the previous cytological studies, those Alnus species distributing in Japan have five types of chromosome numbers (2n=14,28,42,56,112). Combined with paleobotanic evidence, the studies indicated that the Alnus might be originated in Japan.