AOBPreview originally published online on June 26, 2009
Annals of Botany 2009 104(4):757-765; doi:10.1093/aob/mcp153
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Functional and genetic diversity of mycorrhizal fungi from single plants of Caladenia formosa (Orchidaceae)
1 School of Applied Sciences, RMIT University, PO Box 71, Bundoora, VIC 3083, Australia
2 Australasian Native Orchid Society (Melbourne), PO Box 354, Glen Waverley, VIC 3150, Australia
3 Institute of Land & Food Resources, University of Melbourne, 500 Yarra Boulevard, Richmond, VIC 3121, Australia
* For correspondence. E-mail t.huynh{at}rmit.edu.au
Received: 28 January 2009 Returned for revision: 2 April 2009 Accepted: 29 May 2009 Published electronically: 26 June 2009
Background and Aims: Mycorrhizal associations are essential to the plant kingdom. The largest flowering plant family, the Orchidaceae, relies on mycorrhizal fungi for germination, growth and survival. Evidence suggests varying degrees of fungal-host specificity based on a single fungal isolate from a single plant. This paper shows for the first time the diversity of endophytes colonizing in a single plant over consecutive years and the functional significance of this diversity.
Methods: Stem-collars of Caladenia formosa were collected in different seasons and years. Mycorrhizal fungi isolated were tested for their efficacy to induce leafing and genetically determined using ITS-RFLP and sequencing.
Results: Multiple mycorrhizal fungi were repeatedly isolated from a single collar that displayed varying effectiveness in germination percentages and adult leaf length. Additional factors contributed to the isolation of effective mycorrhizal fungi; fungal collection season, year of collection and individual isolates. Surface sterilization only improved the number of isolated mycorrhizal fungi. Dual inoculation did not increase germination. All 59 mycorrhizal fungi effective in germinating seed belonged to one clearly defined ITS (internal transcribed spacer) clade and clustered close to Sebacina vermifera (79–89 % homology). Isolates resulting in the greatest germination were not necessarily those resulting in the greatest survival and growth 1 year after germination.
Conclusion: Single orchid plants contained multiple mycorrhizal fungal strains of one species that had diverse functional differences. These results suggest that our current knowledge of fungal–host specificity may be incomplete due to experimental and analytical limitations. It also suggests that the long-term effectiveness of a mycorrhizal fungus or fungi could only be found by germination and longer-term growth tests rather than genetically.
Key words: Mycorrhizal fungi, genetic diversity, effectiveness, germination, isolation, ITS, seasonal influences, Caladenia formosa, Orchidaceae
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