Are plants in the field already induced? Implications for practical disease control

Plants can be induced to develop enhanced resistance to pathogens by treatment with a variety of biotic and abiotic inducers. The resistance induced is broad spectrum and can be long-lasting, but rarely provides complete disease control, with most inducing agents reducing infection between 20 and 85%. One possible reason for this is that plants in the field are already induced through their continual interactions with the biotic and abiotic environment. This article looks briefly at the evidence for biotic and abiotic induction of resistance and then considers whether plants that are already induced are in any way compromised in their ability to respond to agents that induce resistance. Knowledge of the extent to which plants are already induced in the field and the extent to which resistance can be further induced by application of resistance-inducing agents is likely to be important for effective use of induced resistance in practical crop protection.