narrow group of monophyletic Tulasnella (Tulasnellaceae) symbiont lineages are associated with multiple species of Chiloglottis (Orchidaceae): Implications for orchid diversity

narrow group of monophyletic Tulasnella (Tulasnellaceae) symbiont lineages are associated with multiple species of Chiloglottis (Orchidaceae): Implications for orchid diversity

Premise of the study: The Orchidaceae is characterized by exceptional species diversity. Obligate orchid mycorrhizae are predicted to determine orchid distributions, and highly specific relationships between orchids and fungi may drive orchid diversification. In this study, mycorrhizal diversity was...

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Published in:American journal of botany Vol. 97; no. 8; pp. 1313 - 1327
Main Authors: Roche, Sean A, Carter, Richard J, Peakall, Rod, Smith, Leon M, Whitehead, Michael R, Linde, Celeste C
Format: Journal Article
Language:English
Published: United States Botanical Society of America 01-08-2010
Botanical Society of America, Inc
Subjects:
Biodiversity
Biological taxonomies
Botany
Chiloglottis
Ecological genetics
ectomycorrhizae
Flowers & plants
Fungi
Germination
Haplotypes
ITS
molecular phylogeny
mtLSU
Mycology
National parks
Nonnative species
orchid mycorrhizal fungi
Orchidaceae
Phylogenetics
Plant reproduction
Plants
Speciation
Symbionts
Tulasnellaceae
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Summary:Premise of the study: The Orchidaceae is characterized by exceptional species diversity. Obligate orchid mycorrhizae are predicted to determine orchid distributions, and highly specific relationships between orchids and fungi may drive orchid diversification. In this study, mycorrhizal diversity was examined in the terrestrial, photosynthetic orchid genus Chiloglottis to test the hypothesis of mycorrhizal-mediated diversification in the genus CHILOGLOTTIS: This orchid genus secures pollination by sexual deception, an obligate and highly specific pollination strategy. Here we asked whether the obligate orchid-fungal interactions are also specific. METHODS: Two sequenced loci, the internal transcribed spacer region (ITS) and mitochondrial large subunit (mtLSU), were used to identify fungal isolates and assess fungal species diversity. Symbiotic germination of two species Chiloglottis aff. jeanesii and C. valida were used to assess germination potential of isolates and confirm mycorrhizal association. Key results: Phylogenetic analyses revealed that six representative Chiloglottis species spanning a broad survey of the genus were all associated with a narrow group of monophyletic Tulasnella fungal lineages. CONCLUSIONS: The Chiloglottis-Tulasnella interaction appears to be the first known case of such a narrow symbiont association across a broadly surveyed orchid genus. It appears that the specific pollination system of Chiloglottis, rather than specific orchid-fungal interactions has been the key driving force in the diversification of the genus. These findings also indicate that plant groups with highly specific mycorrhizal partners can have a widespread distribution.
Bibliography:The authors thank Prof. Kingsley Dixon (Director of Science, Kings Park and Botanic Gardens, Perth) for advice on seed germination classification.
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ISSN:0002-9122
1537-2197
DOI:10.3732/ajb.1000049