Histopathological Investigation of Varietal Responses to Cercospora beticola Infection Process on Sugar Beet Leaves

Cercospora leaf spot (CLS) is the most destructive foliar disease in sugar beet (Beta vulgaris). It is caused by Cercospora beticola Sacc., a fungal pathogen that produces toxins and enzymes which affect membrane permeability and cause cell death during infection. In spite of its importance, little is known about the initial stages of leaf infection by C. beticola. Therefore, we investigated the progression of C. beticola on leaf tissues of asusceptible and resistant sugar beet varieties at 12 h intervals during the first five days after inoculation using confocal microscopy. Inoculated leaf samples were collected, and stored in DAB (3,3'-Diaminobenzidine) solution until processed. Samples were stained with Alexa Fluor 488 dye to visualize fungal structures. Fungal biomass accumulation, reactive oxygen species (ROS) production, and the area under disease progress curve were evaluated and compared. ROS production was not detected on any variety before 36 hours post inoculation (hpi). C. beticola biomass accumulation, percentage leaf cell death and disease severity were all significantly greater in the susceptible variety compared to the resistant variety (P