Over 20 years of treating conifers with methyl jasmonate: Meta-analysis of effects on growth and resistance

center dot For more than 20 years, methyl jasmonate (MeJA) has been used to study inducible defenses in conifers and to increase tree resistance to pests and pathogens. Despite the numerous studies on the subject, no attempts have been made to summarize or quantify how MeJA affects resistance and growth in conifers. Here we present a quantitative meta-analysis of the effects of MeJA treatment on the conifer genera Pinus and Picea, two of the most economically and ecologically important tree genera in boreal, temperate, and alpine forests. center dot A literature search yielded 120 relevant papers. We summarized the key experimental methods used in these papers and performed a meta-analysis of how MeJA affects tree growth and resistance to pests and pathogens. center dot The results show that MeJA negatively affects tree growth, with an overall effect size of -0.63. The overall effect size of MeJA for tree resistance was -0.76, indicating that MeJA treatment significantly reduces tree damage caused by biotic stressors. center dot Although our meta-analysis shows that MeJA is effective in enhancing conifer defenses, there are still gaps in our understanding of the durability and ecological consequences of MeJA treatment. We provide suggestions for how future research should be conducted to address these gaps.