Phylogenetic Relationship of Ramie and Its Wild Relatives Based on Cytogenetic and DNA Sequence Analyses

To study the relationship between cultivated ramie (Boehmeria nivea) and its wild relatives and the origin of B. nivea, the karyomorphology of interphase nuclei and chromosome numbers were investigated in 19 species and 5 varieties of ramie and sequences of the internal transcribed spacers (ITS) of nuclear ribosomal DNA and the chloroplast trnL-F were analyzed in 18 species and 9 varieties of ramie. On the basis of cytological observation of interphase karyomorphology, the interphase nuclei of sections Tilocnide and Boehmeria were prochromosome type and those of sections Zollingeriana, Phyllostachys, and Duretia were prochromosome or diffuse type. The cytogenetic examination of B. nivea and its 23 wild relatives showed that 19, 3, 1, and 1 taxa were diploid (2n = 28), triploid (2n = 42), tetraploid (2n = 56), and pentaploid (2n = 70), respectively, of which triploid taxa were all from section Duretia. From the phylogenetic trees based on ITS and trnL-F sequences, Boehmeria taxa were grouped into 3 clades and several subclades. Different individuals or clones of B. clidemioides var. diffusa fell into different clades, indicating the possible hybridization and reticulate evolution among species in Boehmeria, and the introgression between B. nivea and B. clidemioides var. diffusa. The core species of wild ramie resources should not only involve B. nivea and its 3 varieties but also B. malabarica var. leioclada and B. clidemioides var. diffusa. It was inferred that 2 evolution routes existed in Boehmeria: prochromosome evolution line and diffuse evolution line. In the former route, section Tilocnide originated from section Boehmeria. In the latter route, the evolution direction was section Boehmeria → Zollingeriana → Phyllostachys → Duretia. Both routes probably originated from the same ancestor. Based on the morphological traits of interphase nucleus and molecular experiment, close relationships were found among sections Zollongerie, Phyllostachys, and Duretia. However, their systematic relationships based on morphological traits were not supported by the cytological evidence and phylogenetic trees of ITS and trnL-F sequences.

摘 要为了了解苎麻与野生近缘种的系统学关系, 更有效利用野生苎麻资源, 通过细胞学观察和分子标记证据, 对中国苎麻与其24个野生近缘类群进行了系统学分析。细胞学结果表明, 苎麻间期核形态属于田中分类体系的前染色体型, 而其野生近缘种分别属于前染色体型和分散型; 苎麻和23个野生近缘物种(其中15个类群的染色体数目为首次报道)中, 19个为二倍体(2n=28), 而大叶苎麻组3个类群为三倍体(2n=42), 1个为四倍体(2n=56), 1个为五倍体(2n=70)。ITS序列和trnL-F序列分析表明, 苎麻属可分成A(含A1和A2亚分支)、B(含B1和B2亚分支)和C 3个基本分支。根据分析结果本文提出苎麻属的两条演化路线: (1)前染色体型进化路线A1→A2, 即腋球苎麻组→苎麻组; (2)分散型进化路线B→C, 即腋球苎麻组→帚序苎麻组→序叶苎麻组→大叶苎麻组。