Study On The Defense Effect Of Pepper Against Green Peach Aphid Regulated By Jasmonic Acid And Salicylic Acid Elicitor

Pepper is the second largest vegetable variety planted in China and the largest in Hainan Province.Myzus persicae is one of the most harmful organisms in pepper production.It can not only slow down or even stop the growth of pepper plants,but also spread a variety of viruses,leading to the occurrence and prevalence of viral diseases,resulting in a serious reduction in pepper production.Effectively stimulating crop defense responses and improving crop defense against pests and diseases is one of the important ways to control the pepper peach aphid.Studies have shown that jasmonic acid(JAs)and salicylic acid(SAs)are the two most commonly studied elicitors that activate plant immune responses and improve the defense ability of crops against pests and diseases.However,up to now,it is unclear how effective these two types of elicitors are in regulating the defense response of pepper to peach aphids.Therefore,this study focused on resistant and susceptible pepper varieties and peach aphids.By analyzing the effects of external application of methyl jasmonate(MeJA)and methyl salicylate(MeSA)on the development and reproduction of peach aphids,we identified the dose and time effects of two types of elicitors on the defense of resistant and susceptible pepper varieties against peach aphid stress.On this basis,we analyzed the effects of two substances on the antioxidant enzymes,detoxification enzymes The effects of digestive enzyme activity and effector factor expression,as well as the differences in gene expression,synthetase activity,and secondary metabolite content of JA and SA synthesis pathways between aphid resistant and susceptible pepper varieties,were studied to preliminarily clarify the physiological,biochemical,and molecular mechanisms of the two substances in improving the defense response of pepper to peach aphid.The main research results are as follows:Application of MeJA or MeSA can significantly inhibit the development,reproduction,and population growth of the peach aphid,and the appropriate concentrations of MeJA and MeSA were determined to be 0.2 m M and 0.1 m M,respectively.Compared with the control,the development and reproduction of the peach aphid were significantly inhibited after feeding on resistant and susceptible pepper varieties treated with different concentrations of MeJA(0.008 m M,0.04 m M,0.2 m M,1 m M,and 5 m M)or MeSA(0.004 m M,0.02 m M,0.1 m M,0.5 m M,and 2.5 m M),with a significant decrease in egg production and time,a significant prolongation of development duration and egg duration,an intrinsic growth power,and a weekly growth rate The net growth rate also showed a significant downward trend,and the inhibitory effect of applying MeJA or MeSA on the development and reproduction of peach aphids in resistant pepper varieties was significantly better than that in susceptible pepper varieties.Since there were no significant differences in the effects of 0.2,1.00,and 5.0m M of MeJA,as well as 0.1,0.5,and 2.5 m M of MeSA on the development and reproduction of the peach aphid,and they were significantly superior to 0.008 m M and0.04 m M(MeJA),and 0.004 m M and 0.02 m M(MeSA),respectively,it was determined that 0.2 m M and 0.1 m M were the optimal concentrations of MeJA and MeSA,respectively.Exogenous application of MeJA or MeSA significantly affected the gene expression of effector factors and the activities of protective enzymes,detoxification enzymes,and digestive enzymes of the peach aphid,reducing the feeding adaptability of the peach aphid.Moreover,the application effect of MeJA or MeSA on the resistant pepper varieties was better than that of the susceptible pepper varieties,and the sustained effect period for reducing the feeding adaptability of the peach aphid reached8 days.Compared with the control,the gene expression levels of the effect factors MP10 and MP42 of peach aphids fed on resistant and susceptible pepper varieties with 0.2m M MeJA or 0.1 m M MeSA showed a significant increase during the same feeding time,and the increase in aphid resistant varieties was significantly greater than that of susceptible varieties;The expression of the effect factor MPC002 was significantly reduced,but there was no significant difference in the expression after feeding on resistant and susceptible aphid varieties.The results of enzyme activity analysis showed that the activities of protective enzymes such as superoxide dismutase(SOD),catalase(CAT),detoxification enzymes such as acetylcholinesterase(Ach E),carboxylesterase(Car E),glutathione S-transferase(GST),cytochrome P450 enzyme(CYP),and digestive enzymes such as amylase(AMY)were significantly increased compared to the control,and the increase in the activity of resistant varieties was significantly higher than that of susceptible varieties.After applying two elicitors,MeJA or MeSA,the effective period for reducing the feeding adaptability of the peach aphid reached 12 days.Exogenous application of MeJA or MeSA significantly affected the expression of JA and SA synthesis genes,the activity of synthetases,and the content of endogenous JA and SA in both resistant and susceptible capsicum varieties.Moreover,the induction effect of resistant capsicum varieties was better than that of susceptible capsicum varieties,and the induction effect lasted for 10 days.Compared with the control,after applying 0.2 m M MeJA,the expression levels of AOC,AOS,and OPR3,the key genes of JA synthesis pathway,were significantly increased in pepper regardless of whether the pepper was inoculated with peach aphids or not,but there was no significant difference between resistant and susceptible pepper varieties;The expression levels of DAD1 and LOX in aphid resistant pepper varieties were significantly lower than those in susceptible pepper varieties;Analysis of JA synthetase activity showed that the enzyme activities of AOC,AOS,OPR,DAD,and LOX were significantly increased,while only the enzyme activities of DAD and LOX showed an opposite trend to the level of gene expression,and there was no significant difference in all synthetase activities between aphid resistant and susceptible pepper varieties.After applying 0.1m MMeSA,the expression levels of SA synthesis genes EDS5,ICS1,and PAL1 in pepper were significantly higher than those before spraying,regardless of whether the pepper was inoculated with peach aphids or not.The expression levels of PAL1 in resistant pepper varieties were significantly higher than those in susceptible pepper varieties,while the expression levels of EDS5,ICS1 were not significantly different between resistant and susceptible pepper varieties;Analysis of the activities of SA synthase ICS and PAL showed that the enzyme activity in both resistant and susceptible pepper varieties was significantly increased,consistent with the trend of gene expression changes,and the enzyme activity in resistant pepper varieties was significantly higher than that in susceptible pepper varieties.External application of 0.2m M MeJA and 0.1 m M MeSA increased the content of endogenous JA and SA,respectively,and the content of these two endogenous hormones in resistant pepper varieties was significantly higher than that in susceptible pepper varieties.The induction effect of the two elicitors applied externally on the defense signal pathway of JA and SA in resistant pepper varieties was significantly better than that of susceptible pepper varieties,and the induction effect lasted for 12 days.Exogenous application of MeJA or MeSA significantly increased the content of total phenols and flavonoids in both resistant and susceptible capsicum varieties,and the induction effect of resistant capsicum varieties was better than that of susceptible capsicum varieties,with the induction effect lasting for 8 days.Compared with the control,after applying 0.2 m M MeJA or 0.1 m M MeSA,the content of total phenols and flavonoids in the secondary metabolites related to insect defense in the leaves significantly increased compared to before spraying,and the content in the resistant pepper varieties was significantly higher than that in the susceptible pepper varieties.After spraying MeJA for 1 d,2 d,4 d,8 d,10 d,and 12 d,the total phenol content in the resistant pepper varieties was 1.48-fold,1.43-fold,1.32-fold,0.98-fold,1.23-fold,1.31-fold,1.27-fold,1.39-fold,and 1.14-fold,1.06-fold,1.33-fold,1.24-fold,respectively,of the susceptible pepper varieties without or with peach aphid inoculation;After spraying MeSA for 1 d,2 d,4 d,8 d,10 d,and 12 d,the flavonoid content in the resistant pepper varieties was 1.69-fold,1.27-fold,1.22-fold,1.12-fold,1.26-fold,1.20-fold,and 1.10-fold,1.11-fold,1.22-fold,1.39-fold,1.26 fold,and 1.20-fold,respectively,of the susceptible pepper varieties.The effect of applying two elicitors to induce the increase of flavonoids and total phenols content in aphid resistant pepper varieties was significantly better than that in aphid susceptible pepper varieties,and the induction effect lasted for 12 days.