Tandem Repeat rDNA Sequences Derived from Parents Were Stably Maintained in Hexaploids of Drosera spathulata Complex (Droseraceae)

Drosera spathulata complex, which consists of diploid, tetraploid and hexaploid populations, is widely but disjunctively distributed from eastern part of Australia throughout the South East Asian countries, to Japan. Among these populations, high morphological changing has been found in this species. To investigate intraspecific DNA polymorphism, and to infer the polyploid origin, some populations and cultivars of the Drosera spathulata complex and close related species were investigated using molecular cluster analysis with nucleotide sequences of the large Subunit of ribulose-1,5-bisphosphate carboxylase (rbcL), and the internal transcribed spacer (ITS) of 18S-26S nuclear rDNA sequences (ITS). The rbcL analysis to estimate the species as maternal inheritance revealed that the highest similarity to the hexaploid sequence was found in that of the tetraploid. In contrast, the nuclear rDNA analysis clarified that the hexaploid had two types of ITS sequences: One type of the sequence showed the highest sequence similarity to ITS in D. rotundifolia L. genome, while another type of sequence showed the highest sequence similarity to ITS in the tetraploid D. spathulata Labill. genome. These results suggested that the hexaploid genome could be derived from amphiploidizaion between ancestor species of D. rotundifolia as paternal genome, and the tetraploid D. spathulata as maternal genome.