Biocontrol through antibiosis: exploring the role played by subinhibitory concentrations of antibiotics in soil and their impact on plant pathogens

There is abundant prior published information on antibiosis, one of the most studied biocontrol mechanisms for plant pathogens. Depending on their concentration, antibiotics can have various effects on target organisms, a phenomenon known as hormesis. Under complex soil conditions where subinhibitory concentrations of antibiotics are thought to prevail, the mechanism of action responsible for disease reduction through antibiosis is often overlooked, where it is generally assumed that biocontrol occurs through mortality of the pathogen. This concept of dose-dependent response must be taken into account to better understand antibiosis and how it can contribute to biocontrol in various ways. This review aims to focus on how antibiotics can operate and persist in soil, act as signalling molecules and enable interactions between soil microbial communities. It also aims to pinpoint specific examples where low, subinhibitory concentrations of antibiotics, which are widespread under natural soil conditions, can reduce disease symptoms by modulating the pathogen’s transcriptome, rather than by toxicity and death. This highlights the need to better understand and characterize as much as possible the mode of action of antibiosis under various complex environmental conditions, in order to anticipate future development of resistance and loss of efficiency through changes in environmental conditions.