Article

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

Department of Integrative Biology, University of California, 3060 Valley Life Sciences Building, #3140, Berkeley, California 94720, USA.
Molecular Ecology (Impact Factor: 5.84). 03/2005; 14(2):613-26. DOI: 10.1111/j.1365-294X.2005.02424.x
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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.

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    • "Although it has been hypothesized that mycorrhizal specificity is associated with rarity in orchids, the recent proliferation of molecular studies of orchid–fungal relationships is revealing that there is no clear trend between mycorrhizal specificity and the abundance and geographical range size of orchids (McCormick and Jacquemyn, 2014). For example, there are several instances in which rare orchids have been found to utilize multiple fungal species (Shefferson et al., 2005; Jacquemyn et al., 2011; Pandey et al., 2013). As seen in P. deformis, increasingly it is being shown that high mycorrhizal specificity can be associated with widespread host distribution . "
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    • " n g i i n t h e Tu l a s n e l l a c e a e a n d Ceratobasidiaceae ( e . g . , cantharelloid clade ) has been previous - ly reported ( Otero et al . 2002 ; Ma et al . 2003 ; Suarez et al . 2006 ) . Certain photosynthetic orchids , even when sampled over a wide range , have a single dominant species of Rhizoctonia fungus ( McCormick et al . 2004 ; Shefferson et al . 2005 , 2010 ; Irwin et al . 2007 ) . However , fully mycoheterotrophic ( MH ) orchids , which are achlorophyllous and nutritionally dependent on their mycorrhizal fungi , can be colonized by several different ectomycorrhizal ( ECM ) fungi ( e . g . , Russulaceae and Thelephoraceae fungi ) ( Roy et al . 2009 ; Kennedy et al . 2011 ) as well a"
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    • "Moreover, the age of roots and intensity of fungal colonization may be linked. For example, in the photosynthetic orchid genus Cypripedium, fungal colonization differs by root age – only intermediate-aged roots are heavily colonized, while young and old roots are usually devoid of mycorrhizal colonization (Shefferson et al., 2005). Habitat type may have a strong impact on OrM fungal composition . "
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