Moving to the field: effective protection of conifer seedlings against a forest pest by eliciting jasmonate-induced resistance

Abstract: Previous greenhouse studies have shown that jasmonate-inducible responses provide resistance against the pine weevil, a phloem chewer causing large conifer seedling mortalities at field. Here we explore whether elicitation of the immune system in conifer seedlings before planting could be efficient in protecting seedlings at real field conditions. We performed a large collaborative field experiment with four conifer species widely planted in North (Norway spruce and Scots pine) and South Europe (Maritime pine and Radiata pine) in Sweden and Spain, respectively. Seedlings were treated with four methyl jasmonate (MJ) concentrations before planting in an area naturally infested by the weevil. Chemical defences, seedling growth and weevil damage were studied during two growing periods after planting. In general, MJ treated plants showed increased quantitative defences, and were the less attacked, less wounded, less girdled and less killed. Effects were mostly dose dependent, although some interactive effects with species were observed. Even when MJ treatment had a growth cost, height of the treatedplants did not differ too much from that of untreated plants after two years, due to the benefits of inducing defences when the intensity of damage was high. Elicitation of MJ-inducible defences in seedlings at the nursery could be an efficient and environmentally friendly way of preventing the extensive mortalities caused by the weevil after planting. An extended analysis of this experiment is currently under review elsewhere (Zas et al., submitted).