Inducibility of chemical defences by exogenous application of methyl jasmonate is long-lasting and conserved among populations in mature Pinus pinaster trees

Abstract

Induced defences in conifers are an effective strategy that allows individuals to increase resistance against pests and pathogens by optimizing associated costs. Studies exploring inducibility of defences in conifers have usually been conducted in young individuals (i.e., seedlings and saplings) whereby effects were addressed within weeks or months after induction, limiting knowledge and generalization of long-term patterns in mature individuals growing under natural conditions. In addition, few studies have explored how plasticity and genetic differentiation among populations may affect the inducibility of defences in mature trees. We took advantage of two long-term Pinus pinaster common gardens to explore the interactive and independent contribution of genetic differentiation (i.e., variation among populations) and the environment (i.e., plasticity between sites) as drivers of variation in short-term, long-term and systemic inducibility of chemical defences (resin flow, non-volatile resin, phenolics) in response to simulated herbivore damage associated with jasmonate signalling. We provide evidence that the external application of methyl jasmonate increased the production of resin based defences in mature P. pinaster trees for at least two years after its application. We found that inducibility of defences did not differ among populations, but was rather contingent on local environmental conditions. Systemic effects of methyl jasmonate were also observed and suggest that induced responses likely involve complex within-individual reallocation of chemical defences. Our results contribute to better understanding of the ecological and evolutionary relevance of induced defence strategies in conifers and have important implications for integrating forest management practices aiming to improve forest health and resistance to pests and pathogens.