Combined Jasmonic Acid and Ethylene Treatment Induces Resistance Effect in Faba Bean Plants Against Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae)

SIMPLE SUMMARY: The western flower thrips Frankliniella occidentalis (Thysanoptera: Thripidae) is a major pest of vegetable and flower crops worldwide. A feasible and environmentally friendly method to control F. occidentalis is to induce resistance in host plants. In this study, we attempted to induce resistance against F. occidentalis in faba bean plants. We first investigated the effect of different concentrations of jasmonic acid (JA) and ethylene (ET) alone on the oviposition of F. occidentalis. We then used different concentrations of the combined treatment (JA and ET) to evaluate the most suitable concentrations affecting the oviposition and feeding selectivity of F. occidentalis. Second, we examined the effects of mixed exogenous JA and ET treatments on the activities of JA and ET biosynthetic enzymes in faba bean leaves and on the expression levels of JA/ET pathway marker genes. Finally, we evaluated the effects of JA/ET treatment-related induced resistance on the life history and population parameters of F. occidentalis. Our results provide reference data for the control of thrips infestation in faba bean crops via application of exogenous phytohormones. ABSTRACT: Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae) is a serious invasive pest in China. In this study, we determined whether exogenous jasmonic acid (JA) and ethylene (ET) treatments could induce resistance against F. occidentalis in faba bean plants. First, we investigated the effects of different concentrations of JA or ET alone on F. occidentalis and then assessed the effects of optimal concentrations of JA and ET combined. Our results showed that the optimal concertation of JA was 2 mmol/L and ET was 0.5 mmol/L. JA + ET mixture showed the greatest inhibitory effect in terms of oviposition and feeding. JA with ET was found to induce changes in the activities of lipoxygenase (LOX), allene oxide synthase (AOS), polyphenol oxidase (PPO), 1-aminocyclopropane 1-carboxylic acid synthase (ACS), and trypsin inhibitor (TI). This treatment also activated or inhibited the relative expression levels of LOX1, ACO2, ACS2, and AP2/ERF. Treatment of faba bean plants with JA and ET significantly prolonged F. occidentalis development and adult preoviposition period, significantly reduced per-female oviposition, and altered male longevity and offspring demographic parameters. These results indicate that JA with ET can induce defenses against the growth and development of F. occidentalis in faba bean plants.