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Janie Becker - Plant Ecology Lab

Middle Tennessee State University, Murfreesboro, TN

Contribution of fungal diversity to distribution patterns of

the woodland orchid Corallorhiza odontorhiza

The non-photosynthetic myco-heterotroph, Corallorhiza odontorhiza (Orchidaceae), relies almost entirely upon fungi within the genus of the ectomycorrhizal basidiomycete, Tomentella (Thelephoraceae), in order to obtain required nutrients and minerals.  While substantial populations of these orchids are somewhat rare throughout much of their range in the eastern U.S., occasional occurrences of dense populations have provoked this investigation into possible explanations for the limited distribution of C. odontorhiza.  By examining distribution patterns and the genetic diversity of Tomentella spp. obtained from C. odontorhiza rhizomes, ectomycorrhizal (ECM) tree root tips, and from soils found within a C. odontorhiza population, we hoped to determine whether establishment of sustained populations of C. odontorhiza is limited solely by the presence or absence of Tomentella spp., or if there are additional relevant factors.  Using direct sample PCR techniques developed in this lab, DNA sequencing, and DNA fragment length analyses an assessment of Tomentella diversity was gleaned.  Phylogenetic trees compiled from sample sequences revealed very slight genetic heterogeneity between Tomentella individuals sampled from ECM root tips collected immediately beside C. odontorhiza and from those sampled directly from ECM root tips in areas with no historical C. odontorhiza plants.  This evidence, combined with our findings that both sample areas had approximately the same number of Tomentella-infected ECM tips per sample, indicates that the distribution of C. odontorhiza is not explained solely by Tomentella distribution.  Further studies addressing this issue should include examination of abiotic factors affecting the orchids distribution such as soil moisture content, soil particle size, and soil organic content, all of which may affect seed germination as well as survival of both protocorm and adult rhizome.