Induced resistance in agricultural crops: effects of jasmonic acid on herbivory and yield in tomato plants
Plants can be treated with natural plant elicitors to induce resistance to herbivores. To use elicitors in agriculture we must know the net effects of induction on plant yield. For 4 yr, I induced plant resistance to insect herbivores in tomato plants using the natural plant hormone jasmonic acid. Foliar jasmonic acid application increased levels of polyphenol oxidase, an oxidative enzyme implicated in resistance against several insect herbivores. Induced plants received 60% less leaf damage than did control plants. I then looked at the effects of this induction on seedling survivorship, phenology, fruit production, and plant biomass in the presence and absence of herbivores. Induced plants produced fewer ßowers than control plants, but this did not translate into differences in yield between treatments. In addition, there was no difference in yield between induced and control plants under natural and experimentally reduced herbivore levels. This lack of effectonyieldmayhavebeencausedbylowlevels of herbivory in the unmanipulated controls. Thus, it appears that jasmonic acid induces resistance in tomato plants and that this resistance produces no measurable costs to tomato plants. Elicitors such as jasmonic acid may be valuable pest man- agement tools, especially when there are high densities of herbivores that can reduce yield.