Abstract
Tuber mesentericum is an edible European black truffle, apparently easy to recognize, but showing a high degree of genetic variability. In this study, we performed an integrative taxonomic assessment of the T. mesentericum complex, combining a multilocus phylogeographic approach with morphological analyses, and including authentic specimens of Vittadini, and Berkeley and Broome. We performed maximum likelihood phylogenetic analyses, based on single and concatenated gene datasets (ITS rDNA, β-tubulin, elongation factor 1-α), and including all available sequences from previous studies. Phylogenetic analyses consistently recovered three reciprocally monophyletic and well-supported clades: clade I, with a wide range across Europe; clade II, specimens collected mainly in the Iberian, Italian, and Balkan peninsulas; and clade III, specimens collected almost exclusively in central Italy. Genetic distance between clades ranged from 10.4% to 13.1% at the ITS region. We also designed new primer pairs specific for each phylogenetic lineage. Morphology of spores, asci, and peridium were investigated on specimens representing the three lineages. Macro- and micromorphological analyses of ascomata revealed only a few, but not diagnostic, differences between the three phylogenetic lineages, thus, confirming that they are morphologically cryptic. By studying authentic specimens of Vittadini, and Berkeley and Broome, it was possible to identify the three clades as T. mesentericum, Tuber bituminatum, and Tuber suave sp. nov., and to designate an epitype for T. mesentericum s.s. and a lectotype for T. bituminatum. Future investigations on volatile organic compound (VOC) composition are needed to define the aroma repertoires in this species complex.
Highlights
Truffles are hypogenous ascomata, mainly formed by fungi in the Ascomycota and Basidiomycota phyla
Since the advent of molecular phylogenetics, many researchers have worked to revise the taxonomy within the genus Tuber [3,4,5,6]
Phylogenetic analyses based on either single genes or on the concatenated dataset consistently recovered three reciprocally monophyletic clades (Figures 1 and 2) that received maximum support in the concatenated analysis: (i) one clade with the widest range across Europe; (ii) a second clade grouping specimens collected mainly in the Iberian, Italian, and Balkan peninsulas; and (iii) a third clade including specimens collected almost exclusively in central Italy and Greece
Summary
Mainly formed by fungi in the Ascomycota and Basidiomycota phyla. Those in the genus Tuber (Ascomycota, Pezizales), the so-called true truffles, live in mycorrhizal symbiosis with the roots of many trees, shrubs, and herbaceous plants [1]. Tuber species that produce ascomata with a pleasant smell and marketable size are considered edible and, of commercial interest. Edible truffles have traditionally been considered one of the most appreciated and expensive foods, and their cultivation and consumption are rapidly spreading worldwide [2]. About 120 Tuber species have been described and molecularly characterized from Asia, Europe, and Central and North
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