Modes of action for biological control of Botrytis cinerea by antagonistic bacteria

The role of beneficial bacteria in biocontrol of plant diseases, particularly those caused by the necrotrophic fungus Botrytis cinerea, has been investigated by testing many bacteria under laboratory and field conditions. Bacteria may protect plants against B. cinerea by direct antagonistic interactions between biocontrol agents and this pathogen, as well as indirect effects through the induction of host resistance. This review focuses on various bacteria that act as biological control agents (BCAs) of B. cinerea and their associated mechanisms. The modes of action (MoAs) include: i) synthesis of anti-fungal metabolites, such as antibiotics, cell wall-degrading enzymes and volatile organic compounds (VOCs); ii) competition for nutrients and/or a niche; and iii) induction of host resistance. The challenge for development of BCAs is to reduce the variability of efficiency and to prove persistence under a large range of conditions. We discuss the advantages and drawbacks of MoA for future applications of bacteria in the field and in post-harvest storage, as well as combination of different MoAs as a strategy to achieve a more regular efficacy.