Interactions between plant defence signalling pathways: evidence from bioassays with insect herbivores and plant pathogens

1. Sequential damage by attackers is hypothesized to result in reciprocal antagonism (cross-talk) between jasmonic acid (JA) and salicylic acid (SA) defence signalling pathways in plants. However, evidence for this cross-talk is not universal and several studies have found positive (synergistic) or no interaction whatsoever between JA and SA pathways. 2. Here we conducted a meta-analysis of studies on plant-mediated effects of initial attackers on performance of subsequent attackers to test the hypothesis of cross-talk between plant hormonal signalling pathways.3. We found a significant negative mean effect size of JA-inducing initial attackers on both JA- and SA-inducing subsequent attackers, but a non-significant effect of SA-inducing initial attackers on both JA- and SA-inducing subsequent attackers. Effects on subsequent herbivores were contingent on the biology of the initial attacker, with negative effects of JA-inducing initial herbivores and no effect of SA-inducing initial herb...