PHYLOGENETIC DIVERSITY IN SHIITAKE INFERRED FROM NUCLEAR RIBOSOMAL DNA-SEQUENCES

Phylogenetic relationships of the edible shiitake mushroom (Lentinula, Tricholomataceae) were studied using DNA sequences from the internal transcribed spacers (ITS) of nuclear ribosomal DNA. The ingroup consis ted of seven isolates of L. edodes from Japan and Thailand, nine isola tes of L. lateritia from Borneo, Papua New Guinea, and Tasmania, and f ive isolates of L. novaezelandieae from New Zealand. These species des ignations are based on morphological species concepts in Lentinula. Ho wever, because Lentinula isolates from throughout Asia-Australasia are mating compatible, some authors treat all of these as belonging to L. edodes. The outgroup included two isolates of L. boryana from Mexico. Parsimony, distance, and maximum likelihood analyses were performed, with various combinations of taxa, characters, and character codings, and bootstrap and decay index measures of robustness. Alternate topolo gies were evaluated in terms of tree lengths, maximum likelihood ratio s, and Templeton's nonparametric test of parsimony. Results suggest th at there are four independent lineages of shiitake in Asia-Australasia , which provides partial support for the morphologically based species concepts. Lentinula novaezelandieae and L. edodes sensu stricto were supported as monophyletic, but L. lateritia appears to be paraphyletic . A corollary of this is that the morphology of L. lateritia should be plesiomorphic for shiitake, which seems plausible based on outgroup c omparison. In general, there is a strong correlation between the geogr aphic origins of the isolates and the lineages supported. Biogeographi c interpretation of ITS trees suggests that the ancestral area for shi itake in Asia-Australasia is in the South Pacific, which was the most phylogenetically diverse area examined. Phylogenetic analyses includin g previously published ITS2 sequences of three shiitake isolates of un known origin placed the unknown isolates in a group of L. edodes sensu stricto isolates from Japan and Thailand, which suggests that the unk nown isolates are from northeast or continental Asia. ITS-based cladog rams have points of agreement as well as disagreement with previously published mitochondrial DNA-based dendrograms from a subset of the iso lates used in this study. Discrepancies between the ITS and mtDNA tree s could mean that the nuclear ITS and the mtDNA have different evoluti onary histories. However, comparison of mtDNA and ITS data are complic ated by the fact that the mtDNA data are based on pairwise distances, whereas the ITS data are discrete. Practical implications of the resul ts for shiitake breeding and conservation are discussed.