AOBPreview published online on January 19, 2009
Annals of Botany, doi:10.1093/aob/mcn269
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Ectomycorrhizal Inocybe species associate with the mycoheterotrophic orchid Epipogium aphyllum but not its asexual propagules
,*
1 Centre d'Ecologie Fonctionnelle et Evolutive (CNRS, UMR 5175), Equipe Interactions Biotiques, 1919 Route de Mende, 34293 Montpellier cédex 5, France
2 Orchid Museum Takamori, 512-73 Izuhara, Shimoina, Nagano 399-3107, Japan
3 Environment Department, The General Environmental Technos Co., Ltd, 1-3-5 Azuchimachi Chuo-ku, Osaka 541-0052, Japan
4 Fungus/Mushroom Resource and Research Center, Faculty of Agriculture, Tottori University, 4-101 Koyama-minami, Tottori 680-8553, Japan
5 Université Montpellier 2, UMR AMAP Botanique et bioinformatique de l'Architecture des Plantes, 34000 Montpellier, France
6 Dipartimento di Biologia Vegetale dell'Università, Istituto per la Protezione delle Piante – CNR, Viale Mattioli 25, 10125 Torino, Italy
* For correspondence. E-mail ma.selosse{at}wanadoo.fr
Received: 1 June 2008 Returned for revision: 22 September 2008 Accepted: 25 November 2008
Background and Aims: Epipogium aphyllum is a Eurasian achlorophyllous, mycoheterotrophic forest orchid. Due to its rarity, it is often protected, and its biology is poorly known. The identity and pattern of colonization of fungal associates providing carbon to this orchid have not been studied previously.
Methods: Using samples from 34 individuals from 18 populations in Japan, Russia and France, the following were investigated: (a) colonization patterns of fungal associates of E. aphyllum by microscopy; (b) their identity by PCR amplification of nuclear ribosomal ITS carried out on rhizome fragments and hyphal pelotons.
Results and Conclusions: Microscopic investigations revealed that thick rhizomes were densely colonized by fungi bearing clamp-connections and dolipores, i.e. basidiomycetes. Molecular analysis identified Inocybe species as exclusive symbionts of 75 % of the plants investigated and, more rarely, other basidiomycetes (Hebeloma, Xerocomus, Lactarius, Thelephora species). Additionally, ascomycetes, probably endophytes or parasites, were sometimes present. Although E. aphyllum associates with diverse species from Inocybe subgenera Mallocybe and Inocybe sensu stricto, no evidence for cryptic speciation in E. aphyllum was found. Since basidiomycetes colonizing the orchid are ectomycorrhizal, surrounding trees are probably the ultimate carbon source. Accordingly, in one population, ectomycorrhizae sampled around an individual orchid revealed the same fungus on 11·2 % of tree roots investigated. Conversely, long, thin stolons bearing bulbils indicated active asexual multiplication, but these propagules were not colonized by fungi. These findings are discussed in the framework of ecology and evolution of mycoheterotrophy.
Key words: Asexual multiplication, ectomycorrhizae, Epipogium, Inocybe, mycoheterotrophy, orchid mycorrhizae, specificity, symbiont transmission
These two authors equally contributed to this work.
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