Porocercospora seminalis gen. et comb. nov., the causal organism of buffalograss false smut

Abstract

False smut caused by Cercospora seminalis is an important disease of buffalograss (Buchloë dactyloides) affecting seed production. The pathogen prevents normal caryopsis development and causes considerable yield loss and reduced seed germination. The current taxonomic placement of the false-smut causal pathogen in the genus Cercospora is incorrect based on its morphological characteristics and DNA phylogeny. In the present study the phylogenetic position of C. seminalis is clarified based on DNA sequence analysis of three loci namely the internal transcribed spacer (ITS) region, partial nuclear ribosomal large subunit (LSU) and partial sequences of the RNA polymerase II second largest subunit (RPB2). A collection of C. seminalis isolates was made from buffalograss sites near Lincoln, Nebraska. DNA sequence data indicated that Cercospora seminalis is phylogenetically close to but distinct from species of Bipolaris and Curvularia (Pleosporaceae, Pleosporales). Cercospora seminalis morphologically had unique characteristics, namely densely aggregated and repeatedly branched conidiophores arising from a brown stroma, monotretic conidiogenous cells with inconspicuous loci, and scolecosporous conidia with distosepta, and thickened, darkened hila. Porocercospora is introduced as a new genus to accommodate the buffalograss false-smut pathogen.

Keywords: Buchloë dactyloides; Cercospora seminalis; false smut; multigene phylogeny; taxonomy.