Induced resistance in crop protection: an overview
Abstract: Induced resistance has great potential as an effective and environmentally benign means of crop protection. It exploits a plant’s own defence mechanisms, enhancing its ability to resist infection or damage by controlled application of substances that signal biotic or abiotic challenges. Defence elicitation should be proportionate to the threat, ideally priming the plant’s recognition mechanisms to respond faster to actual threats when they are detected. Thus there will be trade-offs if defence is induced unnecessarily. Resistance elicitors can be plant hormonal substances, synthetic compounds or biologically-derived molecules, often cell wall components. They may be used singly, in combination or integrated with conventional crop protectants, the latter at reduced rates. Biotrophic and necrotrophic pathogens can respond differentially to different elicitors and susceptibility can be induced too and therefore for the hemi-biotrophs it is particularly difficult to predict control levels. Host plant genotypes can respond very differently not only at species and genus level but also between cultivars. Efficacy is further dependent on the plant’s physiological state, and many environmental factors and thus nutrition, formulation and adjuvants may have large effects. Until now, in less controlled environments resistance elicitors have generally failed to deliver their full potential. However, they have the potential to change crop protection approaches substantially to manage the microbial environment, enhancing beneficials whilst containing the impact of detrimental organisms, rather than killing broad functional or taxonomic groups. Furthermore, seed produced from such crops have the potential to be more resistant and vigorous through microbial and epigenetic effects.