Trade-offs in plant defense against pathogens and herbivores: A field demonstration of chemical elicitors of induced resistance

Two signaling pathways, one involving salicylic acid and another involving jasmonic acid, participate in the expression of plant resistance to pathoge ns and insect herbivores. In this study, we report that stimulation of syst emic acquired resistance in field-grown tomato plants with the salicylate m imic, benzothiadiazole: (1) attenuates the jasmonate-induced expression of the antiherbivore defense-related enzyme polyphenol oxidase, and (2) compro mises host-plant resistance to larvae of the beet armyworm, Spodoptera exig ua. Conversely, treatment of plants with jasmonic acid at concentrations th at induce resistance to insects reduces pathogenesis-related protein gene e xpression induced by benzothiadiazole, and partially reverses the protectiv e effect of benzothiadiazole against bacterial speck disease caused by Pseu domonas syringae pv. tomato. We conclude that effective utilization of indu ced plant resistance to the multiple pests typically encountered in agricul ture will require understanding potential signaling conflicts in plant defe nse responses.