Bioprospecting Fungal Biocontrol Agents from Florida Agroecosystems Against Celery Early Blight Caused by Cercospora apii

Fungi are a promising source of biological control agents for the management of phytopathogens such as Cercospora apii, the causal agent of celery early blight. Exploring native fungal isolates associated with agroecosystems near celery production is essential for identifying biocontrol candidates and supporting sustainable, integrated disease management strategies. In this study, fungal isolates were obtained from leaves and soil samples collected across agricultural and natural environments and their antagonistic potential against C. apii was evaluated using in vitro assays. A total of 48 fungal isolates were screened for growth inhibition, of which 12 reduced pathogen colony size by more than 50% in vitro, representing five morphological and taxonomic groups: Aspergillus fumigatus, Fusarium spp., Mucor spp., Neopestalotiopsis sp. and Nigrospora sp. Notably, isolates exhibiting the highest antagonistic activity over time were predominantly derived from leaf samples (p < 0.0001). Two isolates, Mucor nidicola KX3187 and M. irregularis KX3197, consistently showed strong inhibition of C. apii in vitro (up to 85%), and M. nidicola significantly suppressed disease development in planta. This preliminary study identifies Mucor nidicola KX3187 as a potential biocontrol candidate that showed promising activity in greenhouse trials for celery early blight and provides a foundation for future studies to further evaluate its potential as a component of sustainable disease management strategies.