Genetic Diversity and Population Structure of Rhododendron canescens, a Native Azalea for Urban Landscaping

in HortScience

Rhododendron canescens is a deciduous azalea native to the southeastern United States that is used in landscaping due to its ornamental qualities. A genotyping-by-sequencing (GBS) approach was taken to characterize the genetic structure and diversity of a R. canescens germplasm collection. Single nucleotide polymorphisms (SNPs) were identified by two software platforms, STACKS and GBS-SNP-CROP. Three distinct R. canescens populations were detected by STRUCTURE analysis with GBS-SNP-CROP data, whereas two populations were distinguished using STACKS data. Principal component analysis (PCA) with data from both SNP pipelines supported the presence of three populations. Statistical results indicated that there was low genetic differentiation between the populations, but relatively high genetic diversity within populations. The inbreeding coefficient of the R. canescens accessions was low, which would be expected with an outcrossing species. These results suggest that there may be a significant level of gene flow between populations of R. canescens.

Contributor Notes

This work was supported by Specialty Crop Block Grant 16-SCBGP-GA-0010, the Azalea Society of America, and the U.S. Department of Agriculture National Institute of Food and Agriculture Hatch project GEO00755. We thank Matthew Chappell for advice and Carol Robacker, Ron Miller, and Charles Andrew for providing azalea material.

Corresponding author. E-mail:

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    Sites of Rhododendron canescens collection in Georgia. Leaf samples from at least four plants were collected per site. P1, filled blue circles; P2, open red circles; P3, cross-marked green circle.

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    Read depth of sequencing data.

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    STRUCTURE analysis. (A) Support for three optimal clusters based on delta K estimates from GBS-SNP-CROP data. (B) STRUCTURE results with GBS-SNP-CROP data. (C) STRUCTURE results with STACKS data.

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    Principal component analysis (PCA). (A) PCA with single nucleotide polymorphism data from STACKS pipeline. Populations P1, P2, and P3 as defined by STACKS analysis. (B) Proportion of variance explained by principal components.

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    Phylogenetic relationships of Rhododendron canescens accessions. A weighted neighbor-joining phylogenetic tree created in DARwin v6.0.

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