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 h erbivores in tomato plants using the natural plant hormone jasmonic acid. F oliar 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 t hen looked at the effects of this induction on seedling survivorship, pheno logy, fruit production, and plant biomass in the presence and absence of he rbivores. Induced plants produced fewer flowers than control plants, but th is did not translate into differences in yield between treatments. In addit ion, there was no difference in yield between induced and control plants un der natural anti experimentally reduced herbivore levels. This lack of effe ct on yield may have been caused by low levels of herbivory in the unmanipu lated controls. Thus, it appears that jasmonic acid induces resistance in t omato plants and that this resistance produces no measurable costs to tomat o plants. Elicitors such as jasmonic acid may be valuable pest management t ools, especially when there are high densities of herbivores that can reduc e yield.