Taxonomic and phylogenetic analysis of Korean Suillus using three molecular markers

Abstract

The genus Suillus Micheli ex S.F. Gray, well-known edible fungi, plays on important roles in coniferous forest as ectomycorrhizal fungi. While this genus is easily characterized with fleshy pileus, glutinous or tomentose cap and small glandular dots on the stipe, it is still difficult to identify species based solely on fruiting body morphology. Currently, around 98 Suillus species have been reported worldwide and 13 species have been reported from Korea. The present study focuses on confirming the phylogenetic relationships and to refine the confused taxonomic state of Korean Suillus using a combination of morphological features and a multi gene analysis of the internal transcribed spacer (ITS), large subunit (LSU) rRNA, RNA polymerase II gene (RPB2). On the basis of molecular identification using the ITS sequences, 11 species based on morphological identification were re-identified as nine species: S. americanus, S. bovinus, S. granulatus, S. grevillei, S. luteus, S. pictus, S. placidus, S. viscidus and the previously unrecorded S. subaureus. Out of 118 specimens used in this study, 51 specimens were misidentified (43% misidentification rate) and Suillus granulatus presented the highest misidentification rate. Also, micro-morphological features were insufficient to differentiate the similar Suillus species. Molecular phylogenetic results using the three markers showed that Suillus species were divided into seven clades, six of which were supported with more than 70% bootstrap values on Neighbor-Joining analysis. However, Molecular phylogenetic patterns do not follow taxonomical classification suggested by previous taxonomist and Suillus species in the same section are divided into separated clades. The ITS and RPB2 phylogenies show clearer relationship among Suillus species, while the LSU phylogeny was less resolved. The consensus tree of three regions was similar to the ITS results and showed clearer differentiation between Korean Suillus species. Furthermore, results of maximum intraspecific dissimilarity analyses of Suillus species in the each of the sections showed that ITS1 sequences of six Suillus species have higher variability compared to the other two fragment of ITS (ITS2, ITS1-5.8S-ITS2), while two Suillus species (S. americanus and S. grevillei) showed higher intraspecific dissimilarity of ITS2. Suillus viscidus showed the highest intraspecific divergence (3.87- 5.37) among Korean Suillus species. In general, interspecific variation of Suillus species in each clade showed a clear barcoding gap between closely related species. ITS sequence provides useful data to distinguish the morphologically variable species and to determine the interrelationships among the Suillus species.