Phylogenetic analysis of Polystigma and its relationship to Phyllachorales

Abstract

Polystigma amygdalinum, which causes red leaf blotch of almond, is one of the few fungal plant pathogens to remain a taxonomic enigma, primarily because it has resisted cultivation and causes almond leaf blotch only in restricted regions of the world. To place this species in the evolutionary tree of life, we amplified its ribosomal DNA internal transcribed spacer region (ITS), 18S small-subunit of ribosomal DNA (SSU rDNA) and 28S large-subunit of ribosomal DNA (LSU rDNA). Our phylogenetic analyses indicate that P. amygdalinum does not group with Phyllachora species (Phyllachorales) which have been thought to be its close relative. Polystigma amygdalinumis here shown to be a relative of Trichosphaeriales and Xylariales and placed in the Xylariomycetidae.