Response Of Western Flower Thrips To Jasmonic Acid And Ethylene-induced Defenses In Broad Bean Plant

The western flower thrips,Frankliniella occidentalis,is an important pest in the world.Because of its small size,strong concealment,short development,high fecundity and wider host range.F.occidentalis has caused a serious damage on vegetables,flowers and other economic crops.Due to the frequently outbreaks of thrips,chemical control is still the main method,but extensive use of chemicals can produce a series of side effects.Therefore,it is very necessary to take a safer and environmentally friendly approach to control thrips.Exogenous phytohormones can induce resistance of host plant to insects and reduce insect pest damage.It is very significant to decrease the use of insecticides and provide a safer ecological environment.Firstly,the effect of different concentrations of jasmonic acid（JA）or ethylene（ET）on F.occidentalis oviposition were studied respectively,and optimal concentrations for each phytohormone were identified.Then the effect of different combined ways of the optimal concentrations of JA and ET on F.occidentalis oviposition and selectivity was determined,and the maximum effect of the combination were assessed.The selected combined treatment of JA and ET were sprayed on faba bean plants to determined its effect on defense enzyme activity,the expression levels of JA/ET pathway marker genes and metabolome.The effect of induced resistance of faba bean plant on the two-sex life parameters of thrips,detoxification enzyme activity and detoxification enzyme gene expression in thrips were also determined.The findings of this study were summarized as follows:1 Effects of exogenous jasmonic acid and ethylene on oviposition and feeding selectivity of Frankliniella occidentalisTo investigate the effect of JA and ET at varying concentrations on oviposition of F.occidentalis,faba bean plants were sprayed with jasmonic acid at 0.1,0.5,1.0,1.5,2.0,2.5 mmol/L and ethylene at 0.1,0.5,1.0,1.5,2.5 mmol/L,respectively.Results showed that the most effective concentrations for inhibiting oviposition were 2.0mmol/L of jasmonic acid and 0.5 mmol/L of ethylene.Further experimentation was tested by combining these optimal concentrations in three different treatments:（1）JA+ET,which represented spraying JA before spraying ET,（2）ET+JA,where JA was sprayed after ET,and（3）JA with ET,in which JA and ET were sprayed simultaneously.Results showed that the simultaneous spraying JA and ET had the strongest inhibitory effect on oviposition and the greatest repellent to F.occidentalis among all three treatments.Additionally,when compared to the control,the mixture of JA and ET exhibited a strong repellent effect on thrips after 6,12 and 24hours.2 Effects of simultaneous spraying JA and ET on the defense of faba bean plantAfter simultaneous spraying JA and ET on faba bean plant,the activities of defense enzyme varied at different time periods.The activities of lipoxygenase（LOX）in faba bean plants were significantly higher than that of the control at 24 h and 72 h,which was 1.45 times and 1.44 times of the control,respectively.The activity of allene oxide synthase（AOS）decreased significantly at 24 hours,while it increased significantly at24 h and 72 h.The activity of polyphenol oxidase（PPO）was significantly higher than that of the control at 24 h and 48 h,which was 136.92%and 136.86%of the control,respectively,but there was no significant difference at 72 h.The activity of 1-aminocyclopropane-1-carboxylic acid synthase（ACS）decreased significantly at 24hours,increased at 72 hours,and showed no difference at 48 hours.The activity of trypsin inhibitor（TI）was significantly higher than that of the control only at 72 h,which was 1.35 times of that of the control,and there was no significant change at 24 h and48 h compared with the control.After simultaneous spraying JA and ET on faba bean plant,the expression of JA/ET pathway genes also significantly changed.Compared with the control at the same time,the expression of LOX1 in faba bean plants increased significantly at 24 h,which was 1.58 times of that of the control,and decreased significantly at 48 h,and there was no significant difference at 72 h.ACO2 was significantly up-regulated only at 48 h,and there was no difference with control at both 24 h and 48 h.ACS2 was significantly down-regulated at 24 h and 48 h.It was significantly up-regulated at 72 h,which was 135.50%of the control.The expression level of AP2/ERF in faba bean plants was not significantly changed at 24 h compared with the control,and the expression levels significantly increased at 48 h and 72 h,which increased by 7.64 times and 2.26times,respectively.The faba bean metabolomics showed that 11 significantly different metabolites were consistently detected.Among them,8 were up-regulated and 3 were down-regulated,with lipid substances being the most abundant.3 Effects of the defense response of faba bean plant induced by JA and ET on the life table parameters of F.occidentalisCompared to F.occidentalis feeding faba bean plants sprayed with water,thrips feeding plant treated with a mixed of JA and ET significantly prolonged the development of egg（3.04 d）,first instar larva（2.23 d）,immatural stage（14.91 d）,pre-oviposition period（3.37 d）,and the total pre-oviposition period（18.56 d）.,The induced response inhibited the oviposition per female（10.08 d）and shortened the male adult longevity（9.29 d）.The intrinsic rate of increase（r=0.05）,finite rate of increase（λ=1.05）,and net reproductive rate（R₀=3.3）of F.occidentalis were significantly decreased,while the mean generation time（T=23.77）was significantly prolonged.However,the gross reproductive rate（GRR=9.2）did not change significantly compared to the control（GRR=10.76）.4 Effects of the defense response of faba bean plant induced by JA and ET on activities of the detoxification enzyme and expression levels of detoxification enzyme gene in F.occidentalisThe activities of multifunctional oxidase（MFO）,carboxylesterase（Car E）,and glutathione-S-transferases（GSTs）were significantly different at 6 h,24 h,and 48 h after F.occidentalis fed on plant than those treated with a mixed of JA and ET.The MFO activity did not change significantly at 6 h and 48 h,but was significantly lower than that of the control at 24 h after F.occidentalis fed on the treated faba bean plants.The activities of Car E and GSTs were significantly higher than those of the control at three time points.The activities of both Car E and GSTs were the highest at 72 h,which was 2.3 times and 1.15 times of that of the control,respectively.The expression levels of P450 gene,Car E gene and GSTs gene in F.occidentalis also changed significantly after feeding on faba bean plants treated with JA and ET.Compared with the control,the expression levels of CYP4-3 in thrips was significantly up-regulated at 6 h,while it was significantly down-regulated at 24 h,and did not change significantly at 48 h.Compared with the control,the expression of CYP4-5 in F.occidentalis significantly decreased at 6 h,and significantly increased by 2.62 times and 3.78 times at 24 h and 48 h after feeding on the mixed treatment of JA and ET.The expression of CYP6-2 in thrips increased significantly at 6 h and 24 h,and decreased significantly at 48 h.The expression levels of CYP6-3 in thrips were significantly higher than that of the control at 6 h after feeding the mixture of jasmonic acid and ethylene.There was no significant difference between the 24 h and the control,and it decreased significantly at 48 h.There was no significant change in the expression of CYP6k1 in the thrips fed with the mixture of JA and ET compared with the control at different times.After mixed treatment of JA and ET,the Car E gene CL4503.Conting2of thrips increased significantly at 6 h and 48 h compared with the control,and there was no difference at 24 h.The expression of GSTs gene Fo GSTd1 in thrips fed with mixed treatment of JA and ET was not significantly different from that of the control at6 h,but significantly increased at 24 h and 48 h.The Fo GSTs1 in thrips was activated when fed the plant sprayed by the mixed treatment of JA and ET compared with the control,which was 1.56 times,1.51 times and 1.36 times of the control at 6 h,24 h and48 h,respectively.The expression of GSTs1 in thrips increased by 151.42%at 6 h,and decreased at 24 h and 48 h.Overall,the results demonstrated that the mixed treatment of JA and ET could enhance the defense response of faba bean plants,which could affect the oviposition and feeding selectivity of F.occidentalis,and inhibited the development and reproduction of thrips.Moreover,F.occidentalis could adapt to the defense response induced by the mixed treatment of JA and ET by changing its own detoxification metabolism.