ARS | Publication request: Leaf spot on Tigergrass caused by Exserohilum rostratum in Florida

Submitted to: Phytopathology
Publication Type: Abstract Only
Publication Acceptance Date: April 30, 2008
Publication Date: June 15, 2008
Citation: Brunings, A., Datnoff, L., Palmateer, A., Locke, J.C., Frantz, J., Krause, C.R. 2008. Leaf spot on Tigergrass caused by Exserohilum rostratum in Florida. Phytopathology. 98(6):S27.

Technical Abstract: Tigergrass (Thysanoleana maxima) is a commercial containerized and landscape ornamental grass from the family Poaceae similar in appearance to bamboo. In the summer of 2006, a leaf spot was first noticed in a South Florida nursery, and the disease has since then been observed in several nurseries and landscapes throughout Miami-Dade county and the Florida Keys. In addition, leaf spots have been observed on young transplants from production greenhouses in Apopka, FL. Symptoms start as minute tan colored flecks often turning chlorotic to necrotic that elongate elliptically between the leaf veins, sometimes with a yellow halo, eventually turning all necrotic. Individual lesions will coalesce into large necrotic elliptical spots to blotches, sometimes interspersed with chlorosis. Infected leaf tips may turn light brown to brown, curl and turn yellow away from the leaf tip. Exserohilum rostratum was consistently isolated from the lesions incubated in moist chambers, and identified based on conidial morphology and ITS1/ITS4 sequencing. Pathogenicity was confirmed by spraying conidia from 7-day old cultures at inoculum densities varying from 103 to 105 conidia/ml with a surfactant (tween20) onto tigergrass plants. Plants were covered with plastic bags overnight and maintained at 25C. Symptoms appeared as early as 18 hours post inoculation, while control plants sprayed with water and tween20 did not develop symptoms. This appears to be the first report of E. rostratum infecting T. maxima in Florida.