Phylogeography of the ectomycorrhizal Pisolithus species as inferred from nuclear ribosomal DNA ITS sequences

The fungal genus Pisolithus is cosmopolitan in warm temperate regions and forms ectomycorrhizal associations with a wide range of woody plants. To delimit phylogenetic Pisolithus species and identify their geographical distribution, 102 collections were made worldwide and their rDNA internal transcribed spacer (ITS) was sequenced. Phylogenetic analyses of these sequences, together with 46 additional GenBank accessions, identified 11 species. A strong phylogeographical pattern was observed related to the native geographical origin of the host plants. In the Holarctic, P. tinctorius was widely distributed, associated with Pinus and Quercus. It has been co-introduced with pines to other biogeographical regions. Several Pisolithus lineages, including P. aurantioscabrosus, occurred in restricted biogeographical regions associated with endemic plants, such as Afzelia in eastern Africa. Pisolithus albus, P. marmoratus and P. microcarpus were associated with Australasian hosts (Eucalyptus, Acacia) and were distributed with their hosts worldwide. By contrast, two additional unnamed species were restricted to Australia. The present study shows that evolutionary lineages within Pisolithus are related to the biogeographical origin of the hosts. In addition, regional floras and endemic plants could act as hosts of endemic species of Pisolithus.