First Report of Tilletia pulcherrima Bunt on Switchgrass (Panicum virgatum) in Texas

Switchgrass seed samples of 'Blackwell' and 'Alamo' from Bailey County, TX were examined for bunt fungi. Fourteen completely bunted seeds of 'Blackwell' and four of 'Alamo' were found. No partially bunted seeds were found. Bunted seeds were darker and occasionally slightly swollen relative to noninfected seeds. Teliospores were globose to subglobose, 21 to 28 × 20 to 27 μm in diameter, dark reddish brown to nearly black, with blunt warts 1 to 1.8 μm long, enveloped in a hyaline sheath, and often with a short apiculus. Sterile cells were globose to subglobose, 17.5 to 22 μm, with smooth, laminated walls as much as 2.6 μm thick, and often with a short apiculus. This bunt was identified as Tilletia pulcherrima Ellis & Galloway on the basis of host and spore morphology (2). The internal transcribed spacer regions 1 and 2, including the 5.8S rDNA, were sequenced from bunted 'Blackwell' seeds (GenBank Accession No. EU915293, WSP 71501). The sequence was distinct from all Tilletia sequences in GenBank, including Tilletia barclayana (Bref.) Sacc. & Syd. on Panicum obtusum Kunth (GenBank Accession No. AF 310169) (1). To our knowledge, this is the first report of T. pulcherrima from switchgrass in Texas. Plant pathologists and regulatory officials should be aware of the potential for misidentification of T. pulcherrima as T. indica Mitra, the Karnal bunt pathogen of wheat that has similar spores, occurs in Texas, and has quarantine status. References: (1) R. Durán and G. W. Fischer. The Genus Tilletia, Washington State University, Pullman, WA, 1961. (2) K. Vánky, Mycotaxon 91:217, 2005.