C. beticola infection monitored by fluorescence microscopy. Imaging leaf infection of sugar beet plants with the wild type Ahlburg and the Ahlburg ctb2 disruption strain 2-1 both transformed to express constitutively DsRed. A and B Bright field images of the leaf surface, demonstrate characteristic leaf spot symptoms of the wild type infection at 21 days after inoculation, while the gene disruption strain did not cause leaf spots. C and D The mycelium of DsRed expressing strains of Ahlburg wild type and Ahlburg ctb2 disruption strain 2-1 growing on the leaf surface was detected with DsRed filterset of Leica MZ FL III microscope. Scale bars: 250 μm.