Root herbivore performance suppressed when feeding on a jasmonate-induced pasture grass

1. Plants defend themselves from insect herbivore attack using a range of physical and chemical defences which are in many cases regulated by phytohormones such as jasmonates. While much more is known about how jasmonates regulate defence against above-ground herbivores (e.g. herbivores of leaves), there is increasing interest in how they influence below-ground defences. 2. For the Poaceae, most below-ground studies focus on highly domesticated cereals. Here it is demonstrated how exogenous application of methyl jasmonate (MeJA) to the leaf blades of a non-domesticated pasture grass (Microlaena stipoides) caused a more than two-fold decrease in relative growth rate (RGR) of a root-feeding chafer (Dermolepida albohirtum). MeJA treatment did not affect root consumption rates, but substantially reduced the efficiency of conversion of ingested food to body mass. 3. Non-targeted metabolomics identified significant changes in the metabolome of MeJA-induced plants, with three compounds (a galactolipid, a trihydroxy fatty acid and a lysophospholipid) found to be correlated with herbivore RGR, although their roles in herbivore defence remain uncertain. 4. This study suggests that an important Australian pasture grass can become better defended against root herbivores via enhanced jasmonate activity.