The complete chloroplast genome of Taraxacum albidum (Asteraceae), a Japanese endemic dandelion.

Taraxacum albidum, a perennial herb of the Asteraceae family, exhibits both tetraploid and pentaploid in Japan. This study sequenced and characterized the complete chloroplast genome of T. albidum, revealing a 151,451 bp sequence with a typical quadripartite structure, comprising one large single-copy (LSC) region of 84,052 bp, one small single-copy (SSC) region of 18,541 bp, and two inverted repeat (IR) regions, IRa and IRb, each 24,429 bp in length. The chloroplast genome, excluding duplicates, contained 113 unique genes, including 79 protein-coding genes, 30 transfer RNA genes, and four ribosomal RNA genes. The GC content of this genome was 37.7%. Phylogenetic analysis revealed that T. albidum is most closely related to T. mongolicum, with the chloroplast genome sequences being nearly identical, differing by only one nucleotide. These findings suggest that the maternal lineage of T. albidum likely originates from T. mongolicum or its closely related species.

Hybridization between European and Asian dandelions (Taraxacum section Ruderalia and section Mongolica): 1. Crossability and breakdown of self-incompatibility.

In order to investigate crossability between the European section Ruderalia Kirschner, H. Øllgaard & Stepánek and the Asian section Mongolica Dahlst. of the genus Taraxacum Wigg., artificial hybridization experiments were carried out. After inter-sectional crosses on the diploid level, Mongolica plants showed high fruit-set, not strikingly different from either the control (within-populational crosses) or inter-specific crosses within the same section. However, a substantial decrease of fruit-set was detected when Ruderalia plants were the seed parents. Electrophoretic analysis revealed that Ruderalia seed parents in inter-sectional crosses showed relatively low out-crossing rates with low fruit-set, whereas Mongolica plants as seed parents showed high out-crossing rates, mostly 100%. These results indicate that the crossing-barrier is stronger in the direction from Mongolica to Ruderalia than vice versa. Crosses between diploid Mongolica (♀) and triploid Ruderalia (♂) were also successful, although fruit-set was far lower than in 2x-2x crosses, a result which confirms previous reports. Contrary to published accounts, it was found by means of electrophoretic analyses that some 87.5 % of the progeny in 2x-3x crosses were not true hybrids but sexual diploids originating from self-fertilization. Only approximately 12.5 % of the progeny were found to be true agamospermous triploid or tetraploid hybrids. A strong doubt is raised concerning reports in the literature which assume that diploid hybrids originate in 2x-3x crosses. The possible reasons why self-incompatibility was broken down by triploid pollen are discussed.

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.

Germination characteristics of native Japanese dandelion autopolyploids and their putative diploid parent species.

Germination characteristics of native Japanese Taraxacum lineages of Taraxacum platycarpum (diploid), T. venustum (triploid and tetraploid), and T. albidum (pentaploid) have been studied at different temperatures. Taraxacum platycarpum ssp. hondoense is the putative diploid parent of T. venustum. Diploid T. platycarpum ssp. hondoense and the polyploids T. venustum and T. albidum are found in different areas of Japan, and distribution differences may reflect divergent ecological and physiological traits among ploidy levels. In this study, to prevent mixing of seeds of different polyploidy we used flow cytometry to examine the ploidy level of the plants from which seeds were collected. Results from seed-germination experiments showed that dependence on temperature of final percentage germination was qualitatively similar for both autopolyploids T. venustum and diploids T. platycarpum--germination was suppressed at high and low temperatures. It was also shown that seed germination of autopolyploids was suppressed more than that of the ancestral diploid at low temperatures and that seed germination for polyploids was higher than for the diploid. Threshold variations at low temperatures might affect the distribution of native dandelions. Taraxacum venustum, which occurs in cool climates, might have developed a distinctly lower germination threshold at low temperatures whereas T. albidum, which is native to warm climates, might have developed an adaptive threshold at high temperatures.