Effect of Methyl Jasmonate on the Thrips Resistance and Physiological Characteristics of Alfalfa
In order to investigate the effect of exogenous methyl jasmonate(MeJA)on the thrips resis-tance of alfalfa,Medicago sativa cv.Caoyuan No.4 was continuous sprayed with distilled water(CK),0.01 mmol/L,0.10 mmol/L,1.00 mmol/L MeJA and 1.00 mmol/L jasmonic acid synthesis inhibitor(DIECA)for 3 days,respectively,and then thrips(Odontothrips loti)was inoculated.The number of thrips was measured after 0 d(no inoculation),7 d and 14 d inoculation,and the changes of relevant physi-ological characteristics(activities of oxidative defense enzymes,contents of secondary metabolites,soluble protein and soluble sugar)of alfalfa leaves under different treatments were performed.The results showed that compared with the CK group,low concentrations of MeJA(0.01 mmol/L and 0.10 mmol/L)signifi-cantly reduced the thrips density on the 7th and 14th day(P<0.05),while treatment with 1.00 mmol/L significantly reduced the thrips density after 14 days thrips feeding,while the DIECA treatment had no sig-nificant effect on the thrips density.Exogenous 0.10 mmol/L MeJA treatment significantly enhanced the activities of peroxidase(POD),phenylalanine ammoniase(PAL),polyphenol oxidase(PPO),lipoxygen-ase(LOX),as well as the contents of tannins and flavonoids in alfalfa leaves without inoculation with thrips(P<0.05).After 7 days of inoculation with thrips,the PPO and LOX activities of alfalfa leaves treated with exogenous MeJA were significantly higher than those of CK,while the SOD and PAL activi-ties and flavonoids content were significantly lower than those of CK(P<0.05).Exogenous DIECA treat-ment significantly enhanced the activity of SOD and soluble protein content(P<0.05),while the activity of POD and PPO,as well as the content of tannins and flavonoids,were significantly lower than those of CK(P<0.05).After 14 days of inoculation with thrips,the activities of POD,glutathione peroxidase(GPX),LOX and the content of tannin in leaves treated with exogenous MeJA were significantly higher than those in CK,while the contents of flavonoids,soluble sugar and soluble protein were significantly lower than CK(P<0.05).In addition,the activities of glutathione reductase(GR)and PAL,as well as the contents of flavonoids,total phenols,soluble protein and soluble sugar,were significantly lower in the exogenous DIECA treatment than those in CK treatment(P<0.05).These results indicated that exog-enous MeJA could enhance the resistance of alfalfa to thrips by regulating its physiological defense response.
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