A fifty-locus phylogenetic analysis provides deep insights into the phylogeny of Tricholoma (Tricholomataceae, Agaricales)

As an ectomycorrhizal fungal genus that contains matsutake and other edible mushrooms, Tricholoma has great economic and ecological significance. However, the phylogenetic relationships within the genus remain unsettled. To clarify the infrageneric relationships of Tricholoma, including the identification of monophyletic subgenera and sections, three phylogenetic analyses were conducted employing single-locus (ITS), five-locus (ITS/RPB2/EF-1α/MCM7/mtSSU) and 50-locus (45 single-copy orthologous genes plus the aforementioned ones) DNA nucleotide sequences. Our data indicated that ITS sequences could serve the species delimitation of Tricholoma in most cases and monophyletic groups recognition in some cases, and the five-locus dataset could resolve a section-level phylogeny of this genus, while the 50-locus dataset could clarify the delimitation of subgenera and settle the relationships among sections within this genus. A fifty-locus dataset was firstly employed to construct a robust phylogeny of Tricholoma. Based on this, a new infrageneric arrangement for the genus Tricholoma, with four subgenera, of which two are in accordance with the previous subgenera Pardinicutis and Sericeicutis, and eleven sections, is suggested. Subgenus Pardinicutis, occupying the basal position, only harbors sect. Pardinicutis, while the subg. Sericeicutis comprises sects. Lasciva and Sericella located at the sub-basal position with good support. Subgenus Terrea is newly erected here and consists of sect. Terrea, sect. Atrosquamosa and two as yet unnamed phylogenetic lineages. Besides an unnamed section-level lineage, subg. Tricholoma consists of sects. Genuina, Muscaria, Rigida, Tricholoma, Fucata and Matsutake, of which the two latter are newly proposed. The previously defined subg. Contextocutis is clustered within subg. Tricholoma and is a synonym of the latter. Tricholoma colossus, T. acerbum and their allies, which used to be allocated in sect. Megatricholoma (or genus Megatricholoma), are relocated to sect. Genuina since they form a strongly supported monophyletic group and share rusty or black spots on lamellae with other species in this section. Taxonomic descriptions of the new infrageneric taxa and a key to subgenera and sections of the genus Tricholoma are presented.