Abstract
The knotweed taxa Fallopia japonica, F. sachalinensis and their interspecific hybrid F. × bohemica are some of the most aggressive invaders in Europe and North America and they are serious threats to native biodiversity. At the same time, they constitute a unique model system for the creation of hybrids and studies of the initiation of evolutionary processes. In the presented study, we focused on (i) examining genetic diversity in selected populations of three Fallopia taxa in the invaded (Poland) and native ranges (Japan), (ii) establishing genome size and ploidy levels and (iii) identifying ribosomal DNA (rDNA)-bearing chromosomes in all of the taxa from the invaded range. We found that the genetic diversity within particular taxa was generally low regardless of their geographical origin. A higher level of clonality was observed for the Polish populations compared to the Japanese populations. Our study suggests that the co-occurrence of F. sachalinensis together with the other two taxa in the same stand may be the source of the higher genetic variation within the F. × bohemica hybrid. Some shift towards the contribution of F. japonica alleles was also observed for selected F. × bohemica individuals, which indicates the possibility of producing more advanced generations of F. × bohemica hybrids. All of the F. sachalinensis individuals were hexaploid (2n = 6x = 66; 2C = 6.01 pg), while those of F. japonica were mostly octoploid (2n = 8x = 88; 2C = 8.87 pg) and all of the F. × bohemica plants except one were hexaploid (2n = 6x = 66; 2C = 6.46 pg). Within the chromosome complement of F. japonica, F. sachalinensis and F. × bohemica, the physical mapping of the rDNA loci provided markers for 16, 13 and 10 chromosomes, respectively. In F. × bohemica, a loss of some of rDNA loci was observed, which indicates the occurrence of genome changes in the hybrid.
Highlights
The knotweed taxa Fallopia: F. japonica var. japonica, F. sachalinensis and the hybrids of these two species, namely F. × bohemica, are considered to be one of the most aggressive plantPLOS ONE | DOI:10.1371/journal.pone.0161854 August 30, 2016Genetic Variation of Invasive Fallopia invaders in both Europe and North America [1]
We recorded the presence of both sexes of F. sachalinensis–females and hermaphrodites were observed at the Jasieniczanka River
No flowers were observed in the Fallopia japonica and F. sachalinensis populations from Japan at the time the material for the presented study was collected
Summary
The knotweed taxa Fallopia: F. japonica var. japonica, F. sachalinensis and the hybrids of these two species, namely F. × bohemica, are considered to be one of the most aggressive plantPLOS ONE | DOI:10.1371/journal.pone.0161854 August 30, 2016Genetic Variation of Invasive Fallopia invaders in both Europe and North America [1]. The native range of F. japonica is Japan, Sakhalin Island, the Kurile Islands, North and South Korea, Taiwan, Vietnam and parts of China, whereas for F. sachalinensis the range is limited to North Japan, Korea, South Sakhalin and the Kurile Islands [2,3,4]. These species were introduced into Europe in the 19th century as decorative garden plants and soon spread into natural habitats [5,6,7]. The first description of the occurrence of F. × bohemica hybrids in Europe was given only just in 1983 [8]
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