Endophytic fungi as biocontrol agents: elucidating mechanisms in disease suppression

Background: Fungal endophytes occur ubiquitously in plants and are being increasingly studied for their ability to support plant health and protect the host from diseases. Using endophytes in disease control provides potential advantages compared to other biocontrol agents since they colonise the plant internally and thereby stay protected from environmental stresses and fluctuations. A thorough understanding of their mechanisms is required in their mutualistic association with plants; both to optimise their efficacy and for registration as plant protection products.Aims: To provide a critical review on the mechanisms employed by endophytic fungi in biological disease control. Furthermore, we draw attention to gaps in our knowledge of the complex interactions between plant, pathogen and endophyte and discuss implications for future research.Methods: Review of literature where endophytic colonisation during the specific interaction has been confirmed.Results: Known disease-reducing mechanisms include direct inhibition of pathogen activity by competition, antibiosis and mycoparasitism and indirect inhibition by induced resistance, where the plant's own defence system is activated to combat the diseases. Relying on in vitro studies of alone can result in misleading conclusions.Conclusions: We need to investigate nature and requirements for establishment of successful plant-endophyte interactions, for development of efficient biocontrol agents.