First report of crown rust (Puccinia coronata var. gibberosa) on blue oat grass (Helictotrichon sempervirens) in the United States

Authors: Demers, Jill; BYRNE, JAN - Michigan State University; Castlebury, Lisa

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/16/2015
Publication Date: 5/1/2016
Citation: Demers, J.E., Byrne, J., Castlebury, L.A. 2016. First report of crown rust (Puccinia coronata var. gibberosa) on blue oat grass (Helictotrichon sempervirens) in the United States. Plant Disease. 100(5):1009.

Interpretive Summary: Fungi are a large and diverse group of organisms that cause serious diseases of crop and forest plants. Knowledge of the host range and geographic distribution of disease-causing fungi is critical for managing the movement of these destructive organisms. Recently a rust fungus was found on leaves of blue oat grass, a popular ornamental grass, in a Michigan nursery. This rust was identified using both morphological and molecular characteristics and determined to be a species previously known only from Europe. This rust fungus is reported for the first time from this host plant and for the first time from the United States. Using these data plant pathologists will be able to monitor and control this disease and plant quarantine officials may be able to prevent the spread of this fungus into other nurseries or other parts of the United States.

Technical Abstract: Ornamental grasses are popular decorative plants, with sales valued at $124 million in the U. S. in 2009. One common ornamental grass is blue oat grass, Helictotrichon sempervirens (Vill.) Pilg., a large blue-green grass native to Europe. In 2011, H. sempervirens plants in a commercial nursery in Berrien County, Michigan were found infected with rust. Light brown, oval uredinia, approximately 0.5–1 mm in size, were observed on the abaxial leaf surfaces parallel to leaf venation. Urediniospores were obovoid to globose, (23–)25–32(–38) µm x (20–)22–26(–31) µm, echinulate with evenly distributed spines, with a yellowish cell wall 1.5–2.5 µm thick. Urediniospores had 6–8 scattered, obscure germ pores. Telia were not observed. DNA was extracted from a specimen deposited in the U. S. National Fungus Collections (BPI), 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 (1). 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 by Liu and Hambleton (3). The H. sempervirens specimen was compared to these newly described species using a maximum likelihood phylogenetic analysis based on ITS2 sequences, and the specimen was identified as Puccinia coronata var. gibberosa (Lagerh.) Joerst. This identification is supported by morphological characters, as the urediniospores are larger than the other newly described species (3) but are similar in size, as well as other characters, to those described for Puccinia coronata var. gibberosa (2). Puccinia coronata var. gibberosa has only been previously reported in Europe infecting grasses in the genera Festuca and Calamagrostis (2,3). To our knowledge, this is the first report of Puccinia coronata var. gibberosa on H. sempervirens, which is important information for developing good disease management strategies for this popular ornamental plant. This is also the first report of P. coronata var. gibberosa in the United States, although it is possible that this species could be common in the United States but has not been previously distinguished from other members of the P. coronata species group due to their morphological similarities. This report will be useful to regulatory officials in determining the geographic range of individual species within P. coronata sensu lato, a very common and widespread pathogen.