Genetic Resources and Crop Evolution

, Volume 66, Issue 1, pp 5–15 | Cite as

Chloroplast sequence data differentiate Maleae, and specifically Pyrus, species in the USDA-ARS National Plant Germplasm System

  • Gayle M. VolkEmail author
  • Adam D. Henk
  • Christopher M. Richards
  • Nahla Bassil
  • Joseph Postman
Research Article


The USDA-ARS National Plant Germplasm System (NPGS) maintains a large collection of Maleae, including 49 Malus taxa, 36 Pyrus taxa, and 24 additional genera with ornamental and plant breeding value. These plant genetic resources are primarily maintained clonally as trees or shrubs in field conditions, and seeds are also conserved for some species. We used NPGS Maleae taxa to assess the genetic diversity across the tribe Maleae and placed Pyrus taxa within this broader context using analytical methods that displayed the genetic relationships as a network, rather than as a traditional dendrogram. Sequence variation from four conserved chloroplast regions unraveled the complex and often reticulate genetic relationships among and within 109 economically important Maleae taxa. In a broad sense, chloroplast haplotypes differentiated Pyrus species within Sections Pyrus and Pashia. The genetic relationships amongst Pyrus species were found to be complex, likely resulting from multiple hybridization and expansion/contraction events during the speciation process. Knowledge of the genetic relationships among Maleae genera and/or species may aid in the selection of materials for use as rootstocks and or breeding (hybridization) programs. Future collection efforts to augment the NPGS accessions within the tribe Maleae will improve the coverage and representation and assure conservation of important Rosaceae genetic resources in the NPGS.


Chloroplast Genetic diversity Maleae Pear Pyrus 



We thank Dr. Kevin Conrad at the U.S. National Arboretum for providing leaf samples for Maleae analyses and for providing an internal manuscript review. We also thank the curation teams at the Corvallis, OR and Geneva, NY repositories for providing leaf materials for genetic analyses. USDA is an equal opportunity provider and employer. Mention of trade names or commercial products in this article is solely for the purpose of providing specific information and does not imply recommendation or endorsement by the U.S. Department of Agriculture.

Compliance with ethical standards

Conflict of interest

The authors have no potential conflicts of interest (financial or non-financial).

Human and animal rights

The authors have no research involving human participants and/or animals.

Supplementary material

10722_2018_691_MOESM1_ESM.xlsx (30 kb)
Supplementary material 1 (XLSX 29 kb)


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Copyright information

© This is a U.S. government work and its text is not subject to copyright protection in the United States; however, its text may be subject to foreign copyright protection 2018

Authors and Affiliations

  • Gayle M. Volk
    • 1
    Email author
  • Adam D. Henk
    • 1
  • Christopher M. Richards
    • 1
  • Nahla Bassil
    • 2
  • Joseph Postman
    • 2
  1. 1.USDA-ARS National Laboratory for Genetic Resources PreservationFort CollinsUSA
  2. 2.USDA-ARS National Clonal Germplasm RepositoryCorvallisUSA

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