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<p>The truffle genus Tuber (Ascomycota, Pezizales, Tuberaceae) produces underground
mushrooms widely sought as edible fungi. Tuber species are distributed throughout
Northern hemisphere forests and form obligate ectomycorrhizal symbiosis with trees
within the Pinaceae, Fagaceae, Betulaceae, and Juglandaceae. </p><p>The transition
to a truffle form (from an epigeous form) has occurred independently, multiple times
in both the Ascomycetes and Basidiomycetes. One instance has given rise to the Tuberaceae,
which is composed entirely of obligate ectomycorrhizal species. Attempts to cultivate
European truffle species T. melanosporum, T. aestivum, and T. borchii are underway
in North America and other parts of the world and have been met with mixed success.</p><p>The
overarching goal of my dissertation is to address the systematics, ecology, and biogeography
of Tuber within a phylogenetic framework. Multiple loci were sequenced from Tuber
ascoma collected worldwide including ectomycorrhizae, though an emphasis was placed
on sampling taxon within North American. Maximum likelihood, maximum parsimony, and
Bayesian inference were used for phylogenetic reconstructions. </p><p>A taxonomic
and phylogenetic overview of the family Tuberaceae is presented in Chapter 1. Tuber
is resolved as monophyletic. In Chapter 2, through greater taxon sampling including
epigeous and hypogeous Helvellaceae outgroups and related South American taxa, a resolved
multi-gene phylogeny of the Tuberaceae and putative epigeous ancestor of Tuber is
presented. A previously unknown South American lineage that contains both epigeous
and hypogeous taxa is resolved as sister to the Tuberaceae. Chapter 3 is focused on
issues of cryptic speciation and taxonomy within the Tuber gibbosum clade. The four
species resolved in the Gibbosum clade appear to be endemic to the Pacific Northwest
and associated primarily with Gymnosperms. Chapter 4 is a meta-analysis of all known
Tuber ITS rDNA sequences (e.g. from Genbank and generated from herbarium collections)
available at the time. These were placed within the Tuber phylogeny to assess species
diversity, long-distance dispersal, and host associations. In total, 120 phylotypes
were detected (based on a 96% similarity criterion). Tuber shows high levels of continental
endemism. I hypothesize that species shared between continents and having low ITS
variability (<1%) are the result of recent human-mediated introduction events. Chapters
5 and 6 are focused on the ectomycorrhizal ecology of the economic truffle T. lyonii,
which is native to Eastern and Southern North America. There is a phenomenon of Tuber
lyonii fruiting in pecan orchards. Pecans (Carya illinoinensis) are in the Juglandaceae,
an understudied ectomycorrhizal plant family. I sampled the ectomycorrhizal communities
of pecan orchards (associated with the production of the North American truffle species
Tuber lyonii). In Chapter 5 I discuss four Tuber taxa discovered in these pecan orchards,
their abundance and haplotype diversity. Chapter 6 examines the ectomycorrhizal communities
across the five pecan orchards sampled. I show that multiple Tuber species, including
Tuber lyonii, are dominant in the ectomycorrhizal community. Chapters 7 and 8 focus
on black truffles in the Melanosporum clade. In Chapter 7 I document that Tuber indicum
has been introduced into North America multiple times, and through ectomycorrhizal
synthesis I demonstrate that this Asian species can associate readily with angiosperm
and gymnosperm hosts endemic to North American. In Chapter 8 I describe a quick and
reliable method for the determination of Tuber melanosporum. The method is based on
direct PCR and species-specific primers and is very useful for rapid diagnostics.
I have adapted this approach for other truffle and mushroom species. </p><p>Three
major findings emerge from my dissertation research: 1) Tuber is more diverse than
previously realized; 2) Tuber exhibits high levels of regional and continental endemism;
3) Taxonomic issues remain in many species complexes worldwide (including the Tuber
candidum complex in North America, the Tuber excavatum complex in Europe, the Tuber
indicum complex in Asia). Taxonomic challenges also remain regarding species known
only from ectomycorrhizal or anamorphic states. The discovery of additional Tuber
species is expected as the truffle flora of undersampled regions become better studied
and incorporated into the Tuberaceae phylogeny.</p>
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