Cytogeography And Molecular Identification Of The Aster Ageratoides Polyploidy Complex In Northeastern Yunnan

Aster ageratoides Turcz., which belongs to Asteraceae, is a famous complex, representing a polyploid series based on x=9, namely2x,3x,4x,5x,6x,7x and8x. According to Ling (1985), two species and13varieties are known in China. Aster ageratoides polyploid complex is widely distributed in China,but so far there has been few research about the cytology and cytogeography of it, and fewer molecular study of the varieties, so further investigation about Aster ageratoides polyploid complex in China is demanded. In this dissertation, we conducted morphological、cytogeographical and molecular research of the complex in Northeastern Yunnan, to investigate the class group of the Aster ageratoides polyploid complex here and the morphological feature、 cellular type and molecular feature between varieties.We also analysed the cytogeographical law between varieties(mainly vertical distribution law) and probed into the origin of varieties and isolation mechanism between varieties.1. MorphologyWe made a morphological investigation to some characters of the Aster ageratoides polyploid complex. And we found many characters such as phyllaries size、lingua size、number of vein of lingua、ovarium size of ray-floret、length of pappum and so on have value for distinguishing the variesties to some extent.2. Cytology and cytogeographyThe Cytology study about44plants revealed that the cellular type of the Aster ageratoides polyploid complex here are mainly diploid and tetraploid,and a few is aneuploid. In Daguan county,we discovered a triploid at an altitude of1500m. Study on Chromosome Karyotype revealed that there are sm-type chromosome in3populations of Aster ageratoides var. microanthus, accountting for about one-third of all studied populations.The karyotype asymmetry of A. ageratoides var. microanthus (2x) is higher than A. ageratoides var.laticorybus(vant).Hand-Mazz and A. ageratoides var.scabulus, in other words, A. ageratoides var. microanthus is more evolutionary.We can speculate that var. microanthus diffuse in advance and there are enough time for the karyotype variation and be retained.We also investigated the distributing charactor and the origin of the variety of Aster ageratoides polyploid complex in Norheast of Yunnan province.Here, var. microanthus (2x) adapt to low altitude invironment, and var.laticorymbus(vant).Hand-Mazz (4x) adapt to higher altitude invironment, then it should originate in the Yunnan-Guizhou Plateau,but var.scabulus (4x) only distribute in low altitude area,it has some connection with its origination from eastern region of China.Besides,we probed into the isolation mechanism of Aster ageratoides polyploid complex between all varieties. In Yanjin county, with var.scabulus (4x) and var. microanthus (4x) sympatry,there is no triploid detected.It shows that there is reproductive isolation between them.In Daguan county, var.laticorymbus and var. microanthus distribute at different lattitude and the reproductive isolation is vertical geographical isolation. The triploid was found at an altitude of1500m.It shows that the prezygotic isolation hasn’t formed between var.laticorymbus and var. microanthus. If there is post-zygotic isolation between them, namely if F1generation can multiply normally,further study is needed.3Molecular systematicsThe molecular systematics study of the Aster ageratoides polyploid complex here shows that the three varieties have their specifically molecular sequence.This provides basis for distinguishing between them.From the heterozygotic DNA sequence of the var.laticorymbus (4x),we can infer that the variety is hybridization origin and the sequence’s concerted evolution imcomplete. A. ageratoides var.laticorymbus is allotetraploid.Through sequence alignment,we found var. microanthus (2x) is not its parent.So var.laticorymbus (4x) is not originate on the spot.The result of the molecular sequencing shows that the triploid found at an altitude of1500m in Daguan county is generated through hybridization of var.laticorymbus and var. microanthus.