Phylogenetic and biogeographic relationships of eastern Asian and eastern north American disjunct Suillus species (Fungi) as inferred from nuclear ribosomal RNA ITS sequences

Species of Suillus produce fleshy, pored mushrooms. They are important symb iotic (ectomycorrhizal) partners of many coniferous trees. The genus includ es several putative eastern Asian and eastern North American disjunct speci es, i.e., the S. americanus-S. sibiricus and S. decipiens-S. spraguei compl exes. Phylogenetic relationships among the groups were determined to furthe r understand the biogeographic pattern. Analyses were based on 40 sequences of the ITS region of the nuclear ribosomal RNA tandem repeats, representin g 18 distinct species/populations. Our phylogenetic analyses suggested that : (1) Chinese and United States' (U.S.) S. spraguei plus S. decipiens form a strongly supported monophyletic group, with North American S. decipiens a nd Chinese S. spraguei being sister taxa; (2) S. americanus, Asian and U.S, S. sibiricus, plus S. umbonatus form a clade supported by a high bootstrap value; and (3) little ITS sequence divergence exists within the latter gro up compared to the S. decipiens-S. spraguei clade. Phylogenetic patterns re vealed by this study imply a close phylogenetic relationship between easter n Asian and eastern North American disjunct population/species of Suillus. These fungi display relatively high host fidelity (at least to the host sub genus level), suggesting potential coevolutionary/comigratory trends. (C) 2 000 Academic Press.