A Phylogeny of the Genus Agaricus Based on Mitochondrial atp6 Sequences

Abstract

The genus Agaricus includes the most eco- nomically-important, commercially-cultivated mush- room in the world, A. bisporus. Effective efforts to improve A. bisporus through breeding will require a greater understanding of the evolutionary relation- ships between A. bisporus and other Agaricus species. We present here the complete mitochondrial atp6 gene of A. bitorquis and amplified homologues from 9 other species of Agaricus, including 6 different iso- lates of A. bisporus. Unexpectedly, only 2 variants of atp6 were found among the 6 isolates of A. bisporus, which had been chosen to represent mitochondrial types thought to be highly divergent based on RFLP data. Although interspecific variation was high, par- simony and maximum likelihood analyses resulted in identical phylogenetic trees for the genus: A. bispo- rus, A. subfloccosus and A. subperonatus were tightly clustered as a single subgroup, whereas the remain- ing species were highly divergent. The species rep- resentatives with the closest proximity to the A. bis- porus cluster were A. bitorquis and A. campestris, which is in agreement with published phylogenies de- rived from nuclear sequence data. Incongruency be- tween this mitochondrial gene-based phylogeny and a phylogeny of linear mitochondrial plasmids found in these same species indicates separate evolutionary histories for the plasmids and their host mitochon- dria.