1. Institute for Plant Diseases, Department of Agricultural and Food Microbiology, University of Bonn, Meckenheimer Allee 168, D-53115 Bonn, Germany; Institute of Physics, University of Bonn, Nussallee 12, D-53115 Bonn, Germany; The J. Bennett Johnston, Sr., Center for Advanced Microstructures and Devices (CAMD), Louisiana State University, 6980 Jefferson Highway, Baton Rouge, Louisiana 70806; and German Research Center for Food Chemistry, Lichtenbergstrasse 4, D-85748 Garching, Germany