Dynamics of cercospora leaf spot disease determined by aerial spore dispersal in artificially inoculated sugar beet fields

Cercospora beticola is one of the most important fungal pathogens of sugar beet, causing cercospora leaf spot (CLS) disease. Due to the decreasing efficacy of various fungicides caused by resistance traits, the development of a sustainable disease management strategy has become more important. Therefore, detailed knowledge about the epidemiology of the pathogen is crucial. Until now, little was known about the spatiotemporal dispersal of C. beticola spores from the primary inoculum source. Rapid detection of C. beticola spores could facilitate a more precise and targeted disease control. Therefore, a TaqMan real-time PCR assay for detection and quantification of C. beticola spores caught with Rotorod spore traps was established. In 2016 and 2017, field trials were conducted to monitor C. beticola aerial spore dispersal and disease development within an inoculated field and in the adjacent noninoculated area. With the established detection method, C. beticola spores were successfully quantified and used as a measure for aerial spore dispersal intensity. The analysis of the spatiotemporal spread of C. beticola spores revealed a delay and decrease of aerial spore dispersal with increasing distance from the inoculated area. Consequently, disease incidence and severity were reduced in a similar manner. These results imply that spore dispersal occurs mainly on a small scale within a field, although long distances can be overcome by C. beticola spores. Moreover, secondary aerial spore dispersal from sporulating leaf spots seems to be the main driver for CLS disease development. These results provide an important basis for further improvement of CLS control strategies.