Colonization and penetration of sugar beet leaves by Ahlburg wild type DsRed and Ahlburg ctb2 disruption strain 2-1 -DsRed. Fluorescence microscopy was performed with a Zeiss fluorescence microscope, using the DsRed filter for detection of the hyphae and UV light to excite blue autofluorescence of the plant cell wall. At 4 days after inoculation, A Ahlburg wild type-DsRed mycelia and B Ahlburg ctb2 disruption strain 2-1-DsRed mycelia were visible on the surface of leaves. C At 4 days after inoculation, the wild type approached stomata and began to penetrate. D The gene disruption strain grew on the surface without entering through stomata at 4 days after infection. Scale bars: A and B = 100 μm, C and D = 20 μm. Abbreviations: ew epidermal cell wall, h hyphae, s stomata, sp stomatal pore, t trichome.