Optimizing Induced Resistance (IR)
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The use of induced systemic resistance and systemic acquired resistance as a strategy for pest management is becoming more common and commercial products are increasingly available to the producer. Despite tremendous advances in the body of knowledge surrounding this method of crop protection, a complete picture of plant immunity is elusive. Despite the missing edges of the map, practical lessons can be drawn from the existing body of work to create a tentative model for optimizing the performance of elicitors of Induced Resistance (IR). The goal of this work is to develop a usable framework that will help local producers and extension agents alike to use the emerging IR products with optimal results, and provide a starting point for on-farm screening. First, a map of induction logic, Figure 1, will guide the user to the likely induction pathway depending on the nature of the stressor. Then, Table 1 and Table 2 should be helpful in verifying that the induction pathway chosen can be used in the context of the specific plant-pathosystem of interest or at least with another pathogen that employs a similar strategy. Tables 1 and 2 will also be helpful in determining the appropriate dosages, active ingredients to look for, and the expected efficacy if available. Finally, the general considerations and Figure 1 should be useful in integrating IR into IPM by pointing out potential negative/positive interactions, costs, tradeoffs and contraindications. The complex nature of these processes necessitates careful research in each product-plant pathosystem system—evolutionary divergence tends to create some surprising outcomes. Also, researchers and producers should be wary of treating IR activators like conventional products. Important differences like yield costs and a lack of direct antimicrobial action creates unique challenges. Yield costs can be minimized by combining the following approaches: using agents or concentrations that prime IR rather than activate direct defenses, using IR when pest pressures are relatively high or at least forecasted to be, activating IR during high light conditions, and carefully keeping abiotic stresses to a minimum. Furthermore, variability can be reduced by using multiple strains of Plant Growth Promoting Rhizobacteria (PGPR) and Arbuscular Mycorrhizal Fungi (AMF), avoiding frequent foliar sprays without an antimicrobial agent in the mix, and tailoring the treatment prescription to the specific plant-pathosystem (i.e. evolutionary divergence).