First Report of Crown Rust ( Puccinia coronata var. gibberosa ) on Blue Oat Grass ( Helictotrichon sempervirens ) in the United States

Ornamental grasses are popular decorative plants, with sales valued at $124 million in the United States in 2009. One common ornamental grass is blue oat grass, Helictotrichon sempervirens(Vill.) Pilg., a large blue-green grass native to Europe. In June 2011, H. sempervirens plants in a commercial nursery in Berrien County, MI, showed signs and symptoms consistent with rust, namely chlorosis and pustule formation. Approximately 25% of the plants in the field had symptoms, with some leaves heavily covered with pustules. Bright orange oval uredinia, partially covered by the epidermis, approximately 0.5 to 1 mm in size, were observed on the adaxial leaf surfaces parallel to leaf venation. Urediniospores were obovoid to globose, (23-)25-32(-38) [mu]m x (20-)22-26(-31) [mu]m, echinulate with evenly distributed spines, with a yellowish cell wall 1.5 to 2.5 [mu]m thick. Urediniospores had 6 to 8 scattered, obscure germ pores. Telia were not observed. DNA was extracted from a specimen deposited in the U. S. National Fungus Collections (BPI 893225), and the nuclear ribosomal internal transcribed spacer region 2 (ITS2) and the 5'end of the large ribosomal subunit (28S) were amplified and sequenced using published protocols (Aime 2006) (GenBank Accession No. KT827286). The rust was identified as Puccinia coronata Corda based on a GenBank BLAST search. P. coronata sensu lato was recently divided into multiple species and varieties (Liu and Hambleton 2013). The H. sempervirens specimen was compared with these new taxa using a maximum likelihood phylogenetic analysis based on ITS2 sequences, and the specimen was identified as Puccinia coronata var. gibberosa(Lagerh.) Joerst (99% nucleotide identity). This identification was confirmed by morphological characters, as the urediniospores are similar in size, as well as other characters, to those described for Puccinia coronata var. gibberosa, (22-)25-32(-35) [mu]m x (20-)21-24(-27) [mu]m (Cummins 1971), but larger than in the other related taxa, which have a mean size less than 22 [mu]m x 19 [mu]m (Liu and Hambleton 2013). Puccinia coronata var. gibberosa has only been previously reported in Europe infecting grasses in the genera Festuca and Calamagrostis(Cummins 1971; Liu and Hambleton 2013). To our knowledge, this is the first report of Puccinia coronata var. gibberosa on H. sempervirens. This is also the first authenticated report of crown rust on Helictotrichon spp. and P. coronata var. gibberosa in the United States. T