| Summary: | Japanese Knotweed s.l. comprises taxa from the genus Fallopia section Reynoutria, and were introduced to Britain from Asia during the 19th century. The hybrids are believed to have arisen since the introduction of the parental species. Inter-simple-sequence-repeat (ISSR) PCR was used to determine genotypes to examine the potential for sexual reproduction of F. x bohemica in Britain. At one site in Wales the distribution of the two parents and the resultant hybrid offspring were mapped, their genotypes assessed, and the relationships between the genotypes discussed. Evidence was found that both clonal spread and sexual reproduction play a role in the distribution of these plants. Twenty-six genotypes of established hexaploid and two of octoploid F. x bohemica were detected, indicative of continuous new recruitment to the population. Three locations in Britain where both male-fertile and male-sterile tetraploid hybrids are found were analysed for both chloroplast haplotype and genotype. Chloroplast haplotypes were determined by RFLP-PCR analysis of the chloroplast region trnC-trnD, and used to identify the direction of the cross that produced the F. x bohemica. Hybridisation was shown to occur in both directions. In total, ten different genotypes of established tetraploid F. x bohemica were detected, with no common genotype found between the different sites. Genetic diversity among British F. sachalinensis was examined. Most were found to be one of two genotypes, either a widespread male-fertile, or a widespread male-sterile clone. A molecular biogeographical study of F. japonica and F. sachalinensis in Japan was undertaken using PCR RFLPs of six chloroplast regions, trnK¹-trnK², trnC-trnD, trnF-trnV, trnH-trnK, trnD-trnT, and trnM-rbcL. The probable region of the source of the introduced material was identified. Additionally a sub-set of the plants was sequenced to better understand the relationships between the native taxa. To complement the molecular analysis, morphological and cytological investigations were also conducted.
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