Taxonomic significance of fucose in the class Urediniomycetes: Distribution of fucose in cell wall and phylogeny of urediniomycetous yeasts

The carbohydrate compositions of cell wall were determined in the strains o f class Urediniomycetes, mainly ballistoconidium-forming yeasts and related taxa. The major component of cell wall was mannose, and glucose was includ ed as the second component, but xylose was not detected in any strain. Out of 41 strains examined, 39 contained galactose, 14 contained arabinose and 12 contained rhamnose. As a minor component, fucose was detested in 30 stra ins but nor in 11 strains. A phylogenetic tree based on 18S rDNA sequences indicated that the fucose-lacking strains, Euyrhrobasidium hasegawianum, Rh odotolura aurantiaca, R. lactosa, R. minuta, Sakaguchia dacryoidea, Sporobo lomyces coprosmae, S. elongatus, S. foliicola, S. gracilis, S. kluyveriniel ii and S. oryzicola, constituted a distinct cluster from those strains whic h contained fucose. This cluster corresponded to one of the five subcluster s, the Erythrobasidium cluster, in the phylogenetic tree of class Urediniom ycetes. The carbohydrate composition of cell wall is believed to reflect th e phylogenetic relationships among basidiomycetous fungi. The presence or a bsence of fucose in cell wall should be regarded as an important phenotypic characteristic in the taxonomy of basidiomycetes.