Tree Genetics & Genomes

, Volume 10, Issue 4, pp 1027–1043 | Cite as

Landscape genetics of Persian walnut (Juglans regia L.) across its Asian range

  • Paola Pollegioni
  • Keith E. Woeste
  • Francesca Chiocchini
  • Irene Olimpieri
  • Virginia Tortolano
  • Jo Clark
  • Gabriel E. Hemery
  • Sergio Mapelli
  • Maria Emilia Malvolti
Original Paper


Persian walnut (Juglans regia L) is an economically important species cultivated worldwide for its wood and nuts. Despite the increasing interest in the development of conservation strategies for walnut germplasm, an accurate and full-scale overview of wild genetic resources of J. regia has not been conducted because natural populations are located in regions of Asia historically difficult to access. In this study, we estimated the genetic diversity and spatial genetic structure of 39 autochthonous Persian walnut populations sampled across its Asian range using 14 neutral microsatellite markers. A landscape genetic overlay approach was applied to detect the areas of current reservoirs of walnut genetic diversity in the Asian range and to evaluate the role of landscape in shaping walnut genetic diversity since the Last Glacial Maximum. Although Persian walnut has been highly manipulated by humans over the last 2,000 years, we determined that patches of high genetic diversity still exist in the Caucasus and mountains of Central Asia where J. regia might have survived after Pleistocene glaciations. We detected a clear separation of Persian walnut into four main genetic clusters centered in (1) western Kyrgyzstan, (2) western and south–central Asia, (3) east–central Uzbekistan, and (4) Xinjiang and Shandong provinces (China). Overlay of maps showed a coincidence between groups of walnut populations and potential barriers to gene flow such as the Hindu Kush, Pamir, Tien Shan, and Himalaya mountains and the Karakum, Kyzyl Kum, and Taklamakan deserts. This study claimed the relevance of the preservation of walnut genetic resources in the Asian range.


Landscape genetics Genetic diversity Population genetic structure Asia Nuclear microsatellites Juglans regia 



This study was supported by the European Community in the framework of the Seventh Framework Programme under the Marie Curie Actions COFUND project “I-MOVE” (No. 267232) and by the CNR-IBAF (Italian National Research Council–Institute of Agro-environmental and Forest Biology, Porano (Terni, Italy). Samples were obtained in the framework of the Bilateral Projects of the Italian Ministry of Foreign Affairs (L. 401.1990) during the years 1998–2010. The authors thank Marcello Cherubini and Daniela Taurchini for their support in the laboratory and Dr. Claudia Mattioni, Andreas Hamann, and Kevin McKelvey for their critical review of the manuscript. Special thanks goes to the memory of Prof. Erìc Germain (INRA-Bordeaux, France), who provided the Caucasian walnut populations under the EU-AIR 3 CT92 0142 and FAIR III PL96 1887 “W-BRAINS” projects. The use of trade names is for the information and convenience of the reader and does not imply official endorsement or approval by the United States Department of Agriculture or the Forest Service of any product to the exclusion of others that may be suitable.

Data Archiving Statement

Sample and population names of Persian walnut collection, geographic location of Persian walnut populations, and microsatellite raw data for 926 Persian walnut genotypes were submitted to the TreeGene Database (; accession number TGDR017).

Supplementary material

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Copyright information

© Springer-Verlag Berlin Heidelberg 2014

Authors and Affiliations

  • Paola Pollegioni
    • 1
    • 2
  • Keith E. Woeste
    • 3
  • Francesca Chiocchini
    • 1
  • Irene Olimpieri
    • 1
  • Virginia Tortolano
    • 1
  • Jo Clark
    • 4
  • Gabriel E. Hemery
    • 5
  • Sergio Mapelli
    • 6
  • Maria Emilia Malvolti
    • 1
  1. 1.CNR Institute of Agro-environmental and Forest BiologyPoranoItaly
  2. 2.Department of Forestry and Natural ResourcesPurdue UniversityWest LafayetteUSA
  3. 3.USDA Forest Service, Hardwood Tree Improvement and Regeneration Center, Department of Forestry and Natural ResourcesPurdue UniversityWest LafayetteUSA
  4. 4.Earth TrustLittle Wittenham, AbingdonUK
  5. 5.Sylva FoundationLittle WittenhamUK
  6. 6.CNR Institute of Agricultural Biology and BiotechnologyMilanItaly

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