High specificity generally characterizes mycorrhizal association in rare lady's slipper orchids, genus Cypripedium

Authors

  • RICHARD P. SHEFFERSON,

    Corresponding author
    1. Department of Integrative Biology, University of California, 3060 Valley Life Sciences Building, #3140, Berkeley, California 94720 USA,
      Richard P. Shefferson, Microbial Ecology Laboratory, Forestry and Forest Products Research Institute, Tsukuba 305-8687, Japan, Fax: (+81) 29 859 0644; E-mail: dormancy@gmail.com
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  • MICHAEL WEIß,

    1. Botanisches Institut, Universität Tübingen, Auf der Morgenstelle 1, D-72076 Tübingen, Germany,
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  • TIIU KULL,

    1. Institute of Zoology and Botany, Estonian Agricultural University, Riia 181, Tartu 51014 Estonia,
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  • D. LEE TAYLOR

    1. Institute of Arctic Biology, University of Alaska, 311 Irving I Building, 902 N. Koyukuk Drive, Fairbanks, Alaska 99775–7000 USA
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Richard P. Shefferson, Microbial Ecology Laboratory, Forestry and Forest Products Research Institute, Tsukuba 305-8687, Japan, Fax: (+81) 29 859 0644; E-mail: dormancy@gmail.com

Abstract

Lady's slipper orchids (Cypripedium spp.) are rare terrestrial plants that grow throughout the temperate Northern Hemisphere. Like all orchids, they require mycorrhizal fungi for germination and seedling nutrition. The nutritional relationships of adult Cypripedium mycorrhizae are unclear; however, Cypripedium distribution may be limited by mycorrhizal specificity, whether this specificity occurs only during the seedling stage or carries on into adulthood. We attempted to identify the primary mycorrhizal symbionts for 100 Cypripedium plants, and successfully did so with two Cypripedium calceolus, 10 Cypripedium californicum, six Cypripedium candidum, 16 Cypripedium fasciculatum, two Cypripedium guttatum, 12 Cypripedium montanum, and 11 Cypripedium parviflorum plants from a total of 44 populations in Europe and North America, yielding fungal nuclear large subunit and mitochondrial large subunit sequence and RFLP (restriction fragment length polymorphism) data for 59 plants. Because orchid mycorrhizal fungi are typically observed without fruiting structures, we assessed fungal identity through direct PCR (polymerase chain reaction) amplification of fungal genes from mycorrhizally colonized root tissue. Phylogenetic analysis revealed that the great majority of Cypripedium mycorrhizal fungi are members of narrow clades within the fungal family Tulasnellaceae. Rarely occurring root endophytes include members of the Sebacinaceae, Ceratobasidiaceae, and the ascomycetous genus, Phialophora. C. californicum was the only orchid species with apparently low specificity, as it associated with tulasnelloid, ceratobasidioid, and sebacinoid fungi in roughly equal proportion. Our results add support to the growing literature showing that high specificity is not limited to nonphotosynthetic plants, but also occurs in photosynthetic ones.

Ancillary