Hybridization between European and Asian dandelions ( Taraxacum section Ruderalia and section Mongolica)2. Natural hybrids in Japan detected by chloroplast DNA marker.

Natural hybridization in Taraxacum between native sexual diploids and introduced agamospermous triploids occurring in Japan was studied by means of chloroplast DNA (cpDNA) marker. We first determined the nucleotide sequences between trnT (UGU) and trnF (GAA) of cpDNA for 22 plants obtained from Japan and Europe. The sequences analyzed were about 1,574 base pairs long. Among all accessions, the total numbers of polymorphic characters were 56 nucleotide substitutions, three insertions/deletions (ins/dels), and one repeat number polymorphism of mononucleotide motif. Of these polymorphic characters, four nucleotides and one ins/del were applicable in the discrimination between Japanese and European taxa of dandelions. We selected the ins/del in an intergenic region between trnL (UAA) 3' exon and trnF (GAA) as a cpDNA marker. Using a newly developed cpDNA marker, 225 plants of putative Taraxacum officinale collected from 11 populations in Niigata City were investigated. Eighty-two percent of them showed a Japanese haplotype of cpDNA, and they were regarded as hybrids. Compared with the previous studies, it is likely that the prevalence of the hybrid plants is a general phenomena at least in urban areas in Japan. The validity of the cpDNA marker for screening Taraxacum hybrids is discussed.