Induction Of Defence In Cereals By 4-FPA Suppresses Insect Pest Populations And Increases Crop Yields In The Field

Synthetic chemical elicitors are regarded as new agents for sustainable crop protection.Many bioactive chemical elicitors were discovered using different kinds of high throughput different screening systems.But only a few elicitors were clarified the mechanism of action.It was previously reported that 4-fluorophenoxyaetic acid(4-FPA)as a chemical elicitor could repel feeding of white-backed planthopper(WBPH)Sogatella furcifera.In the paper the insect-resistant mechanism of 4-FPA was studied.Main contributions of this work are as follows:Our results showthat 4-FPA can play an important role in protecting rice plants from WBPH,brown planthoppers(BPH)Nikparvata lugerts,and small brown planthopper(SBPH)Laodelphax striatellusin laboratory experiment.4-FPA and its degradation product 4-fluorophenol(4-FP)had no direct effect on planthoppers.The effectiveness of 4-FPA as a plant defense response required the deposition of phenolic polymers as a mean to reduce the ability of planthoppers to suck the sap from phloem.Phenolics-H2O2-POD system was supposed to decide the formation of polymers.Phenolics included 4-FPand flavonoids.Because of the mechanical barrier in parenchyma cells outside the vascular bundles,WBPH nymphs experienced great difficulty in inserting the stylets and in reaching the vascular bundles,resulting in the reduced feeding behavior.The formation of 4-FPA-induced polymers could be slowed or inhibited by exogenous MeJA treatment and mechanical funding treatment in addition to gravid female adult infestation,resulting in the decrease of death rate of WBPH nymphs.Interestingly,the above three factors all changed the content of endogenous JA Consequently,JA was thought to be involved in regulating the deposition of phenolic polymers.4-FPA had good control effects on WBPH in the field experiment,up to 74.8%.But its activity was more easily affected by the concentration and application timing.For increasing the controlling efficacy of 4-FPA,it can mix with general pesticides,such as Imidacloprid and Pymetrozine.By decreasing the number of WBPH,4-FPA-treated plots had more yield per plant and seed-setting rate.Our findings show a novel mode of action for induced anti-insect reaction and demonstrate the potential of 4-FPA as an effective chemical elicitor to control the population density of rice planthoppers in field.