印度蔊菜与无瓣蔊菜形态变异特征的比较及分类关系

Comparison of taxonomic morphological characteristics between Rorippa indica and R. dubia

印度蔊菜(Rorippa indica)与无瓣蔊菜(R.dubia)的分类关系仍存在较大争议,为阐明二者的分类学关系,本研究综合利用形态指标测量、DNA相对含量检测、体细胞染色体观察和基于SSR分子标记的遗传距离分析等方法,系统地比较了二者的分类学特征和细胞遗传学差异。结果表明:印度蔊菜(2n=48)为六倍体,无瓣蔊菜(2n=32)为四倍体。同时,前者DNA相对含量约为150,是后者的1.5倍。通过45对SSR分子标记的遗传距离分析得出,相对于球果蔊菜(R.globosa)与欧亚蔊菜(R.sylvestris),二者亲缘关系较近,独立聚类为一支,但在遗传距离为0.23处可以明确划分为两个种。同时,利用角果长度和结籽密度两个形态指标可以将二者明显区分为两个种。另外,二者存在明显的生殖障碍,通过正反交授粉实验得出:印度蔊菜与无瓣蔊菜自花授粉的结实率分别为97.73%和95.65%,而以印度蔊菜为母本的杂交处理结实率为0,以无瓣蔊菜为母本的杂交处理结实率为47.06%,但其种子萌发率为0。综上所述,印度蔊菜与无瓣蔊菜为两个种。

The taxonomic status of Rorippa indica and R.dubia remains controversial.In order to clarify the taxonomic relationship between them,the differences of taxonomic characteristics and cytogenetic between both of them were systematically investigated by means of morphological index measurement,DNA relative content detection,somatic chromosome observation and genetic distance analysis based on SSR markers.Our results showed that R.indica(2 n=48)was hexaploid and R.dubia(2 n=32)was tetraploid.Consistently,the DNA relative content of the former was about 150,which was 1.5 times that of the latter.Genetic distance analysis based on 45 SSR markers indicated sister relationships between R.indica and R.dubia.However,they could be divided into two species when the threshold of genetic distance was set as 0.23,which was the genetic distance between two well separated species,R.globosa and R.sylvestris.Meanwhile,the two taxa could be readily distinguished by pod length and seed density.In addition,obvious reproductive barriers were observed between them.The seed setting rates of self-pollinated R.indica and R.dubia were 97.73%and 95.65%,respectively,while that of R.indica cross-fertilized by the pollens from R.dubia was 0.In comparison,the seed setting rate of R.dubia cross-fertilized by the pollen from R.indica were 47.06%,but the germination rate of these seeds was zero.In conclusion,R.indica and R.dubia should be regarded as two species.