Diversification, spread, and admixture of octoploid strawberry in the western hemisphere

Authors: BIRD, KEVIN - Michigan State University; Hardigan, Michael; RAGSDALE, AARON - National Laboratory Of Genomics And Biodiversity; KNAPP, STEVEN - University Of California, Davis; VANBUREN, ROBERT - Michigan State University; EDGER, PATRICK - Michigan State University

Submitted to: American Journal of Botany
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/18/2021
Publication Date: 10/12/2021
Citation: Bird, K.A., Hardigan, M.A., Ragsdale, A.P., Knapp, S.J., VanBuren, R., Edger, P.P. 2021. Diversification, spread, and admixture of octoploid strawberry in the western hemisphere. American Journal of Botany. 108(11):2269-2281. https://doi.org/10.1002/ajb2.1776.
DOI: https://doi.org/10.1002/ajb2.1776

Interpretive Summary: This study used genetic markers to study the wild species progenitors of cultivated strawberry. It provides additional insights into the origins and relationships of two distinct wild strawberry species, Fragaria chiloensis and Fragaria virginiana, that were previously hybridized to produce the modern strawberry cultivars we see today. The study presents new evidence that Fragaria chiloensis and Fragaria virginiana share a common evolutionary origin, and that different subspecies of Fragaria chiloensis and Fragaria virginiana have naturally hybridized in regions including the northwestern United States. Our understanding of these relationships and species origins is important to inform breeders and geneticists on how to manage strawberry genetic diversity, coordinate future conservation efforts, and employ different strawberry genetic backgrounds for crop improvement.

Technical Abstract: Octoploid strawberry (Fragaria L.) has a complex evolutionary history that has until recently been intractable due to limitations of available genomic resources. While recent work has further uncovered the evolutionary history of the octoploid strawberry, there are still open questions. Much is still unknown about the evolutionary relationship of the wild octoploid species, Fragaria virginiana and Fragaria chiloensis, and gene flow within and among species after the original formation of the octoploid genome. We leveraged a diversity collection of wild octoploid ecotypes of strawberry representing the recognized subspecies and ranging from Alaska to southern Chile, and a high density SNP array to investigate wild octoploid strawberry evolution. Evolutionary relationships are interrogated with phylogenetic analysis and genetic clustering algorithms. Additionally, admixture among and within species is assessed with model-based and tree-based approaches. Phylogenetic analysis revealed that the two octoploid strawberry species are monophyletic sister lineages. The genetic clustering results show substructure between North Americana and South American F. chiloensis populations. Additionally, model-based and tree-based methods support gene flow within and among the two octoploid species, including newly identified admixture in the Hawaiian F. chiloensis subsp. sandwicensis population, possibly from an ancestral F. chiloensis population. F. virginiana and F. chiloensis are supported as monophyletic and sister lineages. All but one of the subspecies recognized within both octoploid species show extensive paraphyly. Furthermore, the phylogenetic relationship among F. chiloensis populations supports a single population range expansion southward from North America. The inter- and intraspecific relationships of octoploid strawberry are complex and suggest substantial and deep gene flow between sympatric populations among and within species.