Defensive responses of Pinus pinaster seedlings to exogenous application of methyl jasmonate: Concentration effect and systemic response

Abstract

Methyl jasmonate (MeJa) is a plant chemical elicitor which has been used to artificially induce chemical defensive responses and resistance against herbivores in many plant species in recent decades. In this paper, we studied the effect of exogenous MeJa application at different concentrations (0, 5, 50, and 100 mM) on growth, chemical defenses and resistance against the large pine weevil Hylobius abietis L in one year old Pinus pinaster Ait. seedlings. We also investigated whether the local application of MeJa on a basal branch would distally elicit defensive responses or growth reductions on the opposite branch and on the upper main stem. Exogenous application of MeJa induced resin accumulation in the stems, and enhanced resistance against H. abietis. The resin content in plants treated with 100 mM was nearly two-fold greater, and the pine weevil consumed 80% less phloem than in control plants. However, concentration of total phenolics in needles was lower in plants treated with the higher MeJa dose, probably because of a local toxic effect. We did not detect any effect of MeJa application on plant growth traits. In addition, the application of MeJa on the experimental branches did not significantly affect the resin content, nor growth rates of the opposite untreated control branches. However, the application of MeJa on the experimental branches significantly increased the resin content in the stem and total phenolics in the needles in the apical stem section of the seedling. These results suggest that the systemic effect of the MeJa induction is restricted to the most valuable parts of the seedlings, and should be considered in further studies aimed to understand the systemic resistance of conifers.