Detection and phylogenetic relationships of Puccinia emaculata and Uromyces graminicola (Pucciniales) on switchgrass in New York State using rDNA sequence information

The species of rust fungi (Pucciniales) inciting disease on switchgrass (Panicum virgatum) grown in bioenergy feedstock systems across the north-central and eastern United States remain unclear. In the present study, the species number and phylogenetic relationships of rust species affecting switchgrass were examined in 2011-2013 at two sites in New York State as well as selected sites in Alabama, Iowa, Nebraska, Pennsylvania, South Dakota, and West Virginia using ribosomal RNA gene data (partial internal transcribed spacer [ITS] 1, complete 5.8 subunit [S] and ITS2, and partial 28S). Uredinial group and teliospore morphology were also utilized to delimit taxa in collection years 2012 and 2013. Maximum likelihood, maximum parsimony, and Bayesian analyses demonstrated two monophyletic clades. Clade I consisted of Puccinia emaculata and included the majority of single-sorus samples across sites, whereas, Clade II included multiple samples from Iowa, Nebraska, and South Dakota. Single-telial samples for Clade I possessed only two-celled teliospores while Clade II samples possessed only one-celled teliospores, and hence, were readily diagnosed morphologically to P. emaculata and Uromyces graminicola, respectively. No U. graminicola sequences exist in GenBank to compare with our Clade II samples; however, based on teliospore morphology, the identity of Clade II taxa is U. graminicola.