Resistance and response of Pinus pinaster seedlings to Hylobius abietis after induction with methyl jasmonate

Experimental induction of plant chemical defences with methyl jasmonate (MeJa) is a valuable tool for understanding the ecology of plant defensive responses. However, few studies have examined whether MeJa-induced defences in conifers are effective against insect herbivores. We studied, in 17 half-sib Pinus pinaster families, (i) the effect of MeJa application on plant growth and on the induction of diterpenoid resin in different sections of the stem; (ii) whether MeJa-induced defences increase the resistance of living pine juveniles against the large pine weevil Hylobius abietis in an in vivo bioassay and (iii) the induction of resin content after weevil wounding. Resin concentration was greater in the upper section of the stem compared with basal sections in both MeJa-induced and non-induced seedlings. Sixty days after MeJa application, treated plants showed 40% greater resin content all along the stem, but reduced height growth compared to control plants. MeJa-induction was effective against the pine weevil, as induced seedlings were 21% less damaged than control plants. Wounding activity by H. abietis produced a strong local defensive response after 48 h, where resin concentration was double that observed in the basal and apical sections not exposed to the insects.