Geographical diversity of Armillaria mellea s. s. based on phylogenetic analysis

Armillaria mellea was once thought to be a morphologically variable species with a wide distribution and a very broad host range. The relatively recent development of an indirect assessment of sexual incompatibility in Armillaria has led to identification of biological species within A. mellea s. l. Partial intergenic spacer region (IGS) sequences of the ribosomal RNA (rRNA) operon have been determined for most of the Northern Hemisphere species of Armillaria, but not for A. mellea s. s. The aim of this study was to determine the phylogenetic relationships among isolates of A. mellea s. s. based on DNA sequences from the IGS as well as the internal transcribed spacer (ITS) regions. The IGS and the ITS sequence data indicate that A. mellea is highly variable but phylogenetically distant from the other species of Armillaria, and there are four separate groups of A. mellea distinguished by their geographical origin: Asia, western North America, eastern North America and Europe. The data suggest that A. mellea populations from different regions are genetically isolated and may be in the process of speciation.