Hiroyuki Shibaike

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.

Molecular genetic mapping and plant evolutionary biology

With the advent of molecular genetic mapping, it is possible to study the genetic basis of natural heritable variation in new ways. Here, three potential uses of molecular genetic mapping in plant ecology and evolutionary biology are discussed; (1) accurate estimation of genetic parameters, (2) understanding speciation and/or adaptation, and (3) investigating whole genome organization. Basic methods for mapping genes and important mapping strategies are outlined. Recent studies are introduced to illustrate progress so far in applying the new methods in ecological and evolutionary research.

Population differentiation in floral and life history traits ofOxalis corniculata L. (Oxalidaceae) with style length polymorphism

A quantitative genetic analysis was conducted on the amounts and distribution of variation of 20 floral, reproductive and life history traits of a self-compatible perennial,Oxalis cornlculata L. (Oxalidaceae). This species comprises two floral morphs, homostyled and long-styled, with different breeding systems. The hierarchical design of the experiments on three homostyled and three long-styled populations allowed partitioning of variation into four levels of organization using nested ANOVAs. Seven of the 20 traits examined were differentiated between homostyled and long-styled populations. Significant genetic variance components were detected in the major traits (114 of the 120 traits) examined for six populations. Average values of variance components among families within a population across 20 traits for homostyled populations were higher than those of long-styled populations. These responses likely reflect the consequences of different levels of selfing and/or mixed mating on genetic variation in the two floral morphs ofO. corniculata. Pearson product-moment correlations for family means of seven traits selected were also calculated. Two groups of trait combinations (i.e., between floral traits, and between reproductive and life history traits) showed significant family mean correlation coefficients. The origins of these varlation patterns found in different populations ofO. corniculata are discussed in terms of the underlying selective regimes operating in each population.