Fitness costs of jasmonic acid-induced defense in tomato, Lycopersicon esculentum

The resource allocation hypothesis is based on the assumption that defenses are costly, but relatively few studies have quantified the reproductive price of induced defenses, which represent the best means of measuring such costs in isolation from the genotypic costs that confound research involving constitutive defenses. Jasmonic acid (JA) is a plant signal molecule involved in the defensive responses of plants. It induces many of the same chemicals that are associated with herbivore damage, and thus offers a means of inducing plants without the removal of leaf area, which incurs its own costs. In tomato plants, JA induced resistance to Manduca sexta and increased levels of two defensive enzymes, polyphenol oxidase and peroxidase. We measured the impact of JA-induced defenses in tomato, Lycopersicon esculentum (Solanaceae), on several variables associated with reproductive success: fruit number, fruit weight, ripening time, time of fruit-set, number of seeds per fruit, total seeds per plant, the relationship between fruit weight and seed number, and germination success. Plants were grown in a pest-free greenhouse and treated biweekly with solvent or with JA at either of two concentrations: 10 mM or 1 mM. The high concentration of JA led to fewer but larger fruits, longer ripening time, delayed fruit-set, fewer seeds per plant, and fewer seeds per unit of fruit weight. The reproductive impact of induction was reduced at the lower dose, but still significant; 1 mM JA resulted in delayed fruit-set and fewer seeds per unit of fruit weight, compared to control plants. Our research indicates that JA-induced defenses impose significant costs on tomato plants.