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 pr ice of induced defenses, which represent the best means of measuring such c osts in isolation from the genotypic costs that confound research involving constitutive defenses. Jasmonic acid (JA) is a plant signal molecule invol ved in the defensive responses of plants. It induces many of the same chemi cals that are associated with herbivore damage, and thus offers a means of inducing plants without the removal of leaf area, which incurs its own cost s. In tomato plants, JA induced resistance to Manduca sexta and increased l evels of two defensive enzymes, polyphenol oxidase and peroxidase. We measu red the impact of JA-induced defenses in tomato, Lycopersicon esculentum (S olanaceae), on several variables associated with reproductive success: frui t number, fruit weight, ripening time, time of fruit-set, number of seeds p er fruit, total seeds per plant, the relationship between fruit weight and seed number, and germination success. Plants were grown in a pest-free gree nhouse and treated biweekly with solvent or with JA at either of two concen trations: 10 mM or 1 mM. The high concentration of JA led to fewer but larg er fruits, longer ripening time, delayed fruit-set, fewer seeds per plant, and fewer seeds per unit of fruit weight. The reproductive impact of induct ion was reduced at the lower dose, but still significant; I 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 sign ificant costs on tomato plants.