Characterization of North American <i>Armillaria</i> species: genetic relationships determined by ribosomal DNA sequences and AFLP markers

<jats:title>Summary</jats:title><jats:p>Phylogenetic and genetic relationships among 10 North American <jats:italic>Armillaria</jats:italic> species were analysed using sequence data from ribosomal DNA (rDNA), including intergenic spacer (IGS‐1), internal transcribed spacers with associated 5.8S (ITS + 5.8S), and nuclear large subunit rDNA (nLSU), and amplified fragment length polymorphism (AFLP) markers. Based on rDNA sequence data, the nLSU region is less variable among <jats:italic>Armillaria</jats:italic> species than the ITS + 5.8S and IGS‐1 regions (nLSU < ITS + 5.8S < IGS‐1). Phylogenetic analyses of the rDNA sequences suggested <jats:italic>Armillaria mellea</jats:italic>, <jats:italic>A. tabescens</jats:italic> and <jats:italic>A. nabsnona</jats:italic> are well separated from the remaining <jats:italic>Armillaria</jats:italic> species (<jats:italic>A. ostoyae</jats:italic>, <jats:italic>A. gemina</jats:italic>, <jats:italic>A. calvescens</jats:italic>, <jats:italic>A. sinapina</jats:italic>, <jats:italic>A. gallica</jats:italic>, NABS X and <jats:italic>A. cepistipes</jats:italic>). Several <jats:italic>Armillaria</jats:italic> species (<jats:italic>A. calvescens</jats:italic>, <jats:italic>A. sinapina</jats:italic>, <jats:italic>A. gallica</jats:italic>, NABS X and <jats:italic>A. cepistipes</jats:italic>) clustered together based on rDNA sequencing data. Based on the isolates used in this study, it appears that techniques based on IGS‐1, ITS + 5.8S, and/or D‐domain/3′ ends of nLSU are not reliable for distinguishing <jats:italic>A. calvescens</jats:italic>, <jats:italic>A. sinapina</jats:italic>, <jats:italic>A. gallica</jats:italic> and <jats:italic>A. cepistipes</jats:italic>. However, AFLP data provided delineation among these species, and AFLP analysis supported taxonomic classification established by conventional methods (morphology and interfertility tests). Our results indicate that AFLP genetic markers offer potential for distinguishing currently recognized North American Biological Species (NABS) of <jats:italic>Armillaria</jats:italic> in future biological, ecological and taxonomic studies.</jats:p>