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Detection of Cerato-Ulmin on Aggressive Isolates of Ophiostoma ulmi by Immunocytochemistry and Scanning Electron Microscopy. A. M. Svircev, Postdoctoral fellow, Faculty of Forestry, University of Toronto, Ontario, Canada M5S 1A1; R. S. Jeng, and M. Hubbes. Adjunct professor, and Professor, Faculty of Forestry, University of Toronto, Ontario, Canada M5S 1A1. Phytopathology 78:322-327. Accepted for publication 8 May 1987. Copyright 1988 The American Phytopathological Society. DOI: 10.1094/Phyto-78-322.

The surface deposition and accumulation of cerato-ulmin by the aggressive isolates of Ophiostoma ulmi were demonstrated using polyclonal antiserum directed against cerato-ulmin, 10050-nm protein A-gold particles, and a scanning electron microscope. The protein A-gold complex was present on the fungal surface in areas containing the toxin cerato-ulmin (CU). The gold label was present on the surface of the vegetative hyphae, synnemata, synnematal spores, perithecia, and ostiolar hairs of the aggressive isolates of O. ulmi. The protein A-gold label was either evenly distributed on the fungal surface or in the form of large surface aggregates. The nonaggressive isolate Q412 of O. ulmi had a low concentration of protein A-gold label on its fungal structures. When the specific CU antiserum was replaced by preimmune serum, a lack of the protein A-gold label was evident on all fungal structures of the aggressive isolate VA of O. ulmi.