Submitted to: Mycologia
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/1/1996
Publication Date: N/A
Interpretive Summary: Morels and truffles are two of the most highly prized macrofungi collected in nature as a food source. Annually this cottage industry represents a multimillion dollar business in the United States. With the recent commercial cultivation of the morel "mushroom" this industry should grow extensively within the next decade along with the need to learn more about the genetic relationships of these fungi. This paper describes the molecular genetic relationships of morels, morel-like fungi, and truffles inferred from phylogenetic analyses of DNA sequence data obtained from two different genes. The results indicate that truffle fungi have at least five independent origins and that the most prized of these, including the white and black truffles classified in the genus Tuber, are related to a group of fungi that grow in an obligate association with vascular plants. This result suggests that the inability to cultivate truffles commercially may be due to its complex nutritional mode as a plant symbiont. Results of these analyses also provide direction for developing a more natural and predictive classification of these ecologically and economically important fungi.
Technical Abstract: Phylogenetic relationships among ascomycetous truffles and the true and false morels were examined by using sequences from two nuclear encoded ribosomal DNA genes. The data set consisted of 18S rDNA and partial 28S rDNA sequences for 29 taxa. Individual and combined data sets were analyzed by maximum parsimony (MP), neighbor-joining (NJ) distance and maximum likelihood (ML) methods. Parsimony analysis of the combined data set, which contained 3 additional published 18S sequences, consisted of 2358 nucleotide characters and yielded a single most parsimonious tree of 1728 steps. The results indicate that the hypogeous ascomycetous truffle and truffle-like taxa studied represent at least 5 independent lineages within the Pezizales. Cladistic analyses of the sequence data suggest several epigeous and most hypogeous taxa have been misplaced taxonomically and a phylogenetically-based classification for these fungi is proposed. Bootstrap analyses show strong support for a Tuberaceae-Helvellaceae clade which is a monophyletic sister group of a Morchellaceae-Discinaceae clade. Rhizina is a sister group to both of these clades in the MP and ML trees while in the NJ tree it is a sister of the Morchellaceae-Discinaceae clade. MP, ML, and NJ tree topologies indicate that Rhizina should be removed from the Helvellaceae and classified in a monotypic family, the Rhizinaceae.