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An ectomycorrhizal symbiosis? a morphological and molecular characterization of Tricholoma magnivelare in Pinus contorta roots from the West Chilcotin Plateau of British Columbia, Canada Bravi, Rebecca Sue

Abstract

The utility of the T. magnivelare/P. contorta ectomycorrhizal classification is evaluated using a strictly anatomical definition of the symbiosis proposed by Jones & Smith (2004) in which the presence of structural features Hartig net, mantle and extramatrical hyphae characterize the mycorrhizal state. A combined molecular and morphological approach was adopted to analyse samples of P. contorta roots collected from beneath T. magnivelare sporocarps from pine stands in four ecosystems in the West Chilcotin Plateau of British Columbia, Canada. Roots mass samples were assessed and four root morphotypes were described; matchstick root, blackened root, fleshy root and cottony root. Two primer sets were developed to amplify the ITS region of the ribosomal DNA in T. magnivelare. Primer set one amplifies all commercially significant T. magnivelare, from across North America including some T. caligatum. Primer set two specifically amplifies T. magnivelare from the Pacific Northwest of the United States and Canada. Primers testing against a suite of 33 other Tricholoma species and 12 other genera demonstrated the primers performed well. Primer set one initially showed strong and specific amplification of the target species but later in the test an apparent contamination problem developed, further testing is recommended to verify this. Primer set two demonstrated a high specificity to T. magnivelare from the Pacific Northwest of the US and Canada and was used to confirm the presence of T. magnivelare in 10 samples each of the root morphologies. In all samples T. magnivelare presence was established. Root morphotypes and root masses were assessed for the presence of the defining structural features of ectomycorrhizae. These features were not consistently observed individually or in combination. A variety of mantle-like structures were observed and all features were observed in association with necrotizing root tissue. It is therefore the concluded that the current classification of the T. magnivelare/P. contorta symbiosis as ectomycorrhizal is not concordant with the definition of the symbiosis adopted for this study nor would it encourage a full appreciation of the complexity of this symbiotic relationship.

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