Tatsuyoshi Morita

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

Abstract.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 Taraxacumofficinale 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.

Clonal diversity in the agamospermous polyploids of Taraxacum hondoense in Northern Honshu, Japan

Chromosome numbers and allozyme variations were surveyed in 74 polyploid populations ofTaraxacum hondoense, in northern Honshu, Japan. Most of the populations (94.4%) consisted of triploid (2n=24), indicating the predominance of this ploidy level. Approximately 42.6% were found to contain tetraploid (2n=32), and a few plants were pentaploid (2n=40). Electrophoretic analysis at6 Pgdh-1 revealed twelve phenotypes with four alleles (including one putative null allele). The triploids showed excessive heterozygosity (82.4%) and all of the tetraploids and pentaploids were heterozygote. Phenotype IV was the most frequent and widely distributed in northern Honshu. Forty five percent of the populations were found to contain multiple phenotypes at 6Pgdh-1. A total of 21 clones were distinguished using three polymorphic loci (6Pgdh-1, Got andMdh), and a considerable amount of clonal diversity was detected both within and among polyploid populations ofT. hondoense. Factors causing multiclonality in agamospermous polyploids are discussed.