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When plants establish outside their native range, their ability to adapt to the new environment is influenced by both demography and dispersal. However, the relative importance of these two factors is poorly understood. To quantify the influence of demography and dispersal on patterns of genetic diversity underlying adaptation, we used data from a globally distributed demographic research network comprising 35 native and 18 nonnative populations of Plantago lanceolata Species-specific simulation experiments showed that dispersal would dilute demographic influences on genetic diversity at local scales. Populations in the native European range had strong spatial genetic structure associated with geographic distance and precipitation seasonality. In contrast, nonnative populations had weaker spatial genetic structure that was not associated with environmental gradients but with higher within-population genetic diversity. Our findings show that dispersal caused by repeated, long-distance, human-mediated introductions has allowed invasive plant populations to overcome environmental constraints on genetic diversity, even without strong demographic changes. The impact of invasive plants may, therefore, increase with repeated introductions, highlighting the need to constrain future introductions of species even if they already exist in an area., Competing Interests: The authors declare no competing interest., (Copyright © 2020 the Author(s). Published by PNAS.)

Background: Salix caprea is a cold-tolerant pioneer species that is ecologically important in Europe and western and central Asia. However, little data is available on its population genetic structure and molecular ecology. We describe the levels of geographic population genetic structure in natural Irish populations of S. caprea and determine the extent of gene flow and sexual reproduction using both chloroplast and nuclear simple sequence repeats (SSRs)., Results: A total of 183 individuals from 21 semi-natural woodlands were collected and genotyped. Gene diversity across populations was high for the chloroplast SSRs (H T  = 0.21-0.58) and 79 different haplotypes were discovered, among them 48% were unique to a single individual. Genetic differentiation of populations was found to be between moderate and high (mean G ST  = 0.38). For the nuclear SSRs, G ST was low at 0.07 and observed heterozygosity across populations was high (H O  = 0.32-0.51); only 9.8% of the genotypes discovered were present in two or more individuals. For both types of markers, AMOVA showed that most of the variation was within populations. Minor geographic pattern was confirmed by a Bayesian clustering analysis. Gene flow via pollen was found to be approximately 7 times more important than via seeds., Conclusions: The data are consistent with outbreeding and indicate that there are no significant barriers for gene flow within Ireland over large geographic distances. Both pollen-mediated and seed-mediated gene flow were found to be high, with some of the populations being more than 200 km apart from each other. These findings could simply be due to human intervention through seed trade or accidental transportation of both seeds and pollen. These results are of value to breeders wishing to exploit natural genetic variation and foresters having to choose planting material.

Background and Aims: Lolium perenne (perennial ryegrass) is the most important forage grass species of temperate regions. We have previously released the chloroplast genome sequence of L. perenne 'Cashel'. Here nine chloroplast microsatellite markers are published, which were designed based on knowledge about genetically variable regions within the L. perenne chloroplast genome. These markers were successfully used for characterizing the genetic diversity in Lolium and different grass species., Methods: Chloroplast genomes of 14 Poaceae taxa were screened for mononucleotide microsatellite repeat regions and primers designed for their amplification from nine loci. The potential of these markers to assess genetic diversity was evaluated on a set of 16 Irish and 15 European L. perenne ecotypes, nine L. perenne cultivars, other Lolium taxa and other grass species., Key Results: All analysed Poaceae chloroplast genomes contained more than 200 mononucleotide repeats (chloroplast simple sequence repeats, cpSSRs) of at least 7 bp in length, concentrated mainly in the large single copy region of the genome. Nucleotide composition varied considerably among subfamilies (with Pooideae biased towards poly A repeats). The nine new markers distinguish L. perenne from all non-Lolium taxa. TeaCpSSR28 was able to distinguish between all Lolium species and Lolium multiflorum due to an elongation of an A(8) mononucleotide repeat in L. multiflorum. TeaCpSSR31 detected a considerable degree of microsatellite length variation and single nucleotide polymorphism. TeaCpSSR27 revealed variation within some L. perenne accessions due to a 44-bp indel and was hence readily detected by simple agarose gel electrophoresis. Smaller insertion/deletion events or single nucleotide polymorphisms detected by these new markers could be visualized by polyacrylamide gel electrophoresis or DNA sequencing, respectively., Conclusions: The new markers are a valuable tool for plant breeding companies, seed testing agencies and the wider scientific community due to their ability to monitor genetic diversity within breeding pools, to trace maternal inheritance and to distinguish closely related species.

Picea sitchensis, Sitka spruce, is of interest to forestry as both a conservation species and a highly productive crop. Its native range stretches from Alaska to California, and it is hence distributed across a large environmental cline with areas of local adaptation. The IUFRO collection, established in 1968–1970, consists of 81 provenances of commercial and scientific interest spanning this native range. We used genotyping-by-sequencing on 1177 genotypes, originating from 80 of the IUFRO provenances which occupy 19 geographic regions of the Pacific Northwest, resulting in an SNP database of 36,567 markers. We detected low levels of genetic differentiation across this broad environmental cline, in agreement with other studies. However, we discovered island effects on geographically distant populations, such as those on Haida Gwaii and Kodiak Island. Using glaciation data, alongside this database, we see apparent post-glacial recolonization of the mainland from islands and the south of the range. Genotyping the IUFRO population expands upon the use of the collection in three ways: (i) providing information to breeders on genetic diversity which can be implemented into breeding programs, optimizing genetic gain for important traits; (ii) serving a scientific resource for studying spruce species; and (iii) utilizing provenances in breeding programs which are more tolerant to climate change. [ABSTRACT FROM AUTHOR]