Genetic variation in inducibility in two Mediterranean pines

Abstract: Pine trees are able to respond to insect and fungus attacks eliciting a wide array of responses. Particularly, the production of terpenoid-based chemical defences is involved in resistance mechanisms against many pest and pathogens in pine trees. Production of those defences is not cost free, and theory predicts that production of secondary metabolites is inversely related with other plant fitness correlates. Increased susceptibility to pests and diseases is, indeed, a common side-effect of enhancing productivity in many tree breeding programs. Induced defences, i.e. those that are activated after biotic damage, are assumed to have evolved as a cost-saving strategy, as costs of induced resistance materialize only when strictly necessary. Despite breeding for resistance is emerging as an important tool to diminish the impact of forest pests and diseases on managed forests, to date little attention has been paid to the possibility of improving forest resistance through breeding for improving inducibility. Besides, inducibility, the potential for expressing induced defences or induced resistance, is emerging as a relevant trait in explaining the overall resistance of conifer species at field conditions. In previous research we have found that that jasmonate-induced resistance is effective increasing resistance against chewing insects in pine species. We found evidences that terpenoids-based defences show a negative genetic correlation with growth potential, however induced defences did not. Here we performed two greenhouse experiments with 35 half-sib families belonging to two breeding populations of Pinus pinaster and P. radiata, two main forest tree species in SW Europe and other temperate regions. Then we elicited induced defences in half of the plants with methyl-jasmonate following established procedures. We found that inducibility of chemical defences is genetically variable within populations, allowing the possibility of breeding for inducibility.