Defining species in Tulasnella by correlating morphology and nrDNA ITS-5.8S sequence data of basidiomata from a tropical Andean forest

Abstract

The genus Tulasnella comprises important orchid mycobionts. Molecular phylogenetic studies on nrITS-5.8S sequences of Tulasnella species previously isolated from mycorrhizas of epiphytic orchids from a tropical Andean forest showed genomic variability among clones which was difficult to interpret as intra- or interspecific variations or to correlate with described Tulasnella species. To improve this situation, we collected basidiomata of Tulasnella in an Andean forest, studied part of the sequences of fungal ribosomal genes and correlated molecular data with the morphology of the specimens. Within five basidiomata displaying slight morphological variability, we found inter-specimen nrITS1-5.8S-ITS2 variability corresponding to proportional differences of less than 1% except for one clone with 5.1% divergence. Results indicate that the slightly variable basidiomata should be considered as one species, which is morphologically tentatively assigned to the Tulasnella pruinosa complex. However, comparison of nrITS1-5.8S-ITS2 sequences, including sequences of T. pruinosa from other origins, indicate that Tulasnella sp. is only distantly related to the T. pruinosa specimens included in the analyses. Sequences of all morphologically similar and taxonomically well-identified species are required to decide whether the basidiomata analyzed in the present study represent a new species. The new sequences are rather similar to sequences obtained previously from mycorrhizae of epiphytic orchids of the same area indicating mycorrhizal potential of this fungus.