Mixed Impacts of the Mycovirus Fusarium Culmorum Phenuivirus 1 on Fusarium culmorum : Laboratory and In Planta Investigations

ABSTRACT The mycovirus Fusarium culmorum phenuivirus 1 (FcPV1) infects the wheat pathogen Fusarium culmorum , a causal agent of Fusarium head blight (FHB). FHB remains a major threat to cereal cultivation, and the potential of biological control approaches, including the use of mycoviruses, has been suggested for its mitigation. In this study, we describe the biological characterisation of FcPV1, which is a single‐stranded, negative‐sense RNA mycovirus from the Phenuiviridae family. FcPV1 was detected in our previous study, and here we examine its impact on fungal growth and virulence by assessing the pathogenicity of infected F . culmorum on wheat under laboratory to semifield conditions. In laboratory experiments, the presence of FcPV1 resulted in no discernible phenotypic changes, but it was readily transmitted vertically to conidia and horizontally to Fusarium graminearum and other F . culmorum strains. In a greenhouse pot experiment with FHB‐susceptible and ‐resistant wheat, FcPV1 infection appeared to induce hypervirulence, while under semifield conditions, it seemed to result in hypovirulence. In the susceptible cultivar, FcPV1 infection decreased biomass‐adjusted nivalenol concentrations by approximately 40%, whereas deoxynivalenol increased by 28%. To our knowledge, this is the first study comparing mycovirus effects in laboratory, greenhouse and semifield environments. Our findings highlight the complexity of mycovirus–host interactions and the importance of environmental context, emphasising that potential biological control using mycoviruses should be assessed across varying complexities, including semifield and field conditions. This study challenges the notion that mycoviruses are typically cryptic, emphasising that their effects may only manifest under specific environmental conditions and measured parameters.