Abstract
Cercospora beticola is a fungal pathogen of sugarbeet (Beta vulgaris L. ssp. vulgaris) that causes Cercospora leaf spot (CLS). Unfortunately, C. beticola has proven adaptable to current management practices due in part to high levels of genetic diversity found in most field populations. The phyllosphere is composed of the above ground areas of a plant that serve as a habitat for microbes, which can be influenced by abiotic and biotic stressors. We hypothesized that the sugarbeet phyllosphere harbors bacterial communities that may have properties to ward off plant pathogens like C. beticola. To that end, CLS-infected sugarbeet leaves were utilized to create a collection of culturable epiphytic bacteria. A total of 447 bacterial isolates were sequenced from CLS-resistant and -susceptible cultivars across five sampling timepoints. Cercospora beticola isolates were challenged with bacteria from the collection to ascertain antagonistic phenotypes. The assays revealed that Burkholderia contaminans reduces fungal growth without direct mycelial contact or via volatile compounds. Bacterial and fungal RNA-seq was conducted to provide insight into the interactions between B. contaminans and C. beticola. Secondary metabolite molecules putatively involved with C. beticola growth inhibition will be discussed. Identification of the compound(s) responsible for inhibition could provide us with a new management tool for CLS.