Catch me if you can - On the track of the Cercospora spores

Cercospora beticola is the most important leaf spot disease in sugar beet. The disease spreads by conidiospores, which are mainly dispersed by wind and rain. Due to decreasing efficacies of various fungicides used for Cercospora leaf spot control, it becomes more important to develop a sustainable disease management strategy. Therefore, detailed knowledge of the pathogen dispersal is crucial. Previous studies focused on disease dynamics in the field and on the relation between spore flight and disease development. Today, it is not known how C. beticola spores and by this the disease are spread from an inoculum source. A rapid detection of C. beticola spores could facilitate a more time-specific and targeted control of the leaf spot disease. For detection and quantification of C. beticola spores from Rotarod spore traps a DNA extraction method and TaqMan qPCR assay were established. In 2016 and 2017, a field trial was conducted from June or July to August near Gottingen, respectively. Spore flight of C. beticola and disease development were monitored within an inoculated area and in different distances to it. No fungicides were applied within the trial. With the established detection method C. beticola spores were successfully quantified from spore traps. The quantified DNA amounts could be used as a measure of the spore flight intensity. With regard to the spatiotemporal spread of the spores and the disease severity, in 2017 a delay and decrease of the spore flight occurrence and intensity as well as disease severity development was observed. In 2016 a similar trend was found. These results imply, that the disease likely spreads on field scale and over short distances. Moreover, especially the secondary spore flight, originating from sporulating leaf spots, appeared to be responsible for a severe disease development. The results of this study investigated the dynamics of spore and disease spread of Cercospora leaf spot in Central Europe for the first time. Hereby, the potential of using the spore flight for further purposes like disease monitoring or management decisions becomes clear.