ARS | Publication request: Exserohilum Leaf Spot on Tigergrass

Submitted to: Plant Health Progress
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: September 24, 2009
Publication Date: December 15, 2009
Repository URL: http://hdl.handle.net/10113/43908
Citation: Brunings, A.M., Datnoff, L.E., Palmateer, A.J., Locke, J.C., Krause, C.R. 2009. Exserohilum Leaf Spot on Tigergrass. Plant Health Progress. DOI:10.1094/php-2009-1215-01-RS.

Interpretive Summary: A leaf spot of unknown identity was observed on tigergrass plants obtained for research use from a commercial plant supplier. The leaf spot appeared similar to one seen on tigergrass planted in the landscape and at a commercial nursery. Following observation of leaf spot development in the laboratory, isolation and culturing of spores isolated from the spots, inoculation of unaffected tigergrass plants with the cultured spores, and reisolation following development of leaf spots, the causal agent of the disease was determined to be the fungal pathogen Exserohilum rostratum. Conidial morphology and germination pattern matched the literature (Sivanesan’s key) description for this pathogen and although this pathogen has been reported on other hosts, tigergrass represents a new host record.

Technical Abstract: Tigergrass (Thysanolaena maxima (Roxb.) Kuntze ) is a popular ornamental grass grown throughout landscapes in South Florida. In the summer of 2006, a leaf spot was observed on tigergrass in the landscape and a commercial nursery in Homestead, FL. The causal agent of the leaf spot was isolated, characterized and identified as Exserohilum rostratum (Drechsler) Leonard & Suggs. At high inoculum densities, symptoms were apparent as early as 12 hours after inoculation, and caused widespread necrosis. Conidia of E. rostratum were visualized in association with the lesions while engaged in the infection process. This is a new host record for Exserohilum rostratum.