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Title: First report of Tilletia pulcherrima on switchgrass (Panicum virgatum L.) in Texas

item Castlebury, Lisa

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/8/2008
Publication Date: 12/1/2008
Citation: Carris, L.M., Castlebury, L.A., Zale, J. 2008. First report of Tilletia pulcherrima on switchgrass (Panicum virgatum L.) in Texas. Plant Disease. 92:1707.

Interpretive Summary: Switchgrass is a fast-growing plant that is being considered for large-scale production as a source of biofuels. However, knowledge of the plant pathogens that cause diseases of this plant is limited. In examining switchgrass seed grown in Texas, a fungus was discovered that completely replaces the seed tissue with fungal spores. This disease is caused by a bunt fungus that was identified as Tilletia pulcherrima using morphological characteristics. In addition this fungus was sequenced to determine an accurate identification. This bunt fungus was not known previously to occur in Texas and can be confused with the Karnal bunt fungus of wheat, which also occurs in Texas. This research will be used by plant pathologists who are developing strategies to control the disease caused by this bunt fungus and by quarantine officials who need to accurately distinguish this bunt fungus of switchgrass from Karnal bunt spores in wheat.

Technical Abstract: Switchgrass seed samples of cultivars ‘Blackwell’ and ‘Alamo’ from Bamert Seed Company, Muleshoe, Texas, and grown in Texas were examined microscopically for bunt fungi. Fourteen completely bunted seeds of ‘Blackwell’ and four in ‘Alamo’ were detected in 100 g samples of each. Teliospores were globose to subglobose, 21-28 x 20-27 µm diam (mean + S.D. = 24.3 + 2.3 x 23.8 + 2.3 µm), dark reddish-brown to nearly black, with blunt warts 1-1.8 µm long, and enveloped in hyaline sheath, often with short apiculus. Sterile cells were globose to subglobose, 17.5-22 (mean + S.D. = 19.7 + 2.1 µm), with thick, smooth, laminated walls up to 2.6 µm thick, often with short apiculus. This smut was identified as Tilletia pulcherrima Ellis & Galloway. Surface-sterilized teliospores did not germinate after three weeks on water agar at room temperature (20-24 C) or 15 C. The ITS rDNA regions were sequenced from bunted ‘Blackwell’ seeds. The sequence was distinct from Tilletia sequences in GenBank, including Tilletia barclayana (Bref.) Sacc. & Syd. on Panicum obtusum Kunth (AF 310169).