Chemical Mechanism of Exogenous Jasmonic Acid-Induced Resistance in Rose Against Spodoptera exigua (Lepidoptera: Noctuidae)

Jasmonic acid (JA) plays an important role in the indirect plant-mediated interactions between rose powdery mildew (Podosphaera pannosa [Wallr.: Fr.] de Bary) and Spodoptera exigua (Hübner) (Lepidoptera: Noctuidae) on their shared host Rosa chinensis Jacquin. Bioassays showed that the total number of eggs laid by S. exigua on rose twigs decreased significantly after the twigs were treated with exogenous JA. Gas chromatography coupled with mass spectrometry (GC-MS) showed that the volatile organic chemicals (VOCs) from roses, including alkanes, terpenes, aldehydes, ketones, alcohols, and esters, were significantly changed following treatment with JA. Based on gas chromatography-electroantennographic detection (GC-EAD) and GC-MS analysis, the electrophysiological responses of S. exigua moths could be elicited by 8 compounds from the JA-induced roses, including 3-carene, 1-dodecanol, methyl stearate, 1-tetradecanol, hexadecane, eucalyptol, β-myrcene, and 1-iodododecane. Among these chemicals, the first 6 exhibited significant repellent activity to ovipositional behaviors of the gravid moths, while the latter 2 were attractive. The inhibition index of methyl stearate at a concentration of 15 mg/ml reached 65.12%. On the other hand, the quantity of the first 6 chemicals increased significantly and the latter two decreased due to the JA induction. These results reveal a new mechanism for resistance in rose plants against S. exigua. After JA induction, the rose plants appear to up-regulate the biosynthesis of the chemicals with repellent activities against S. exigua and, in the meantime, down-regulate the attractant chemicals.