Physiological And Biochemical Responses Of Alternanthera Philoxeroides To Stresses Associated With Agasicles Hygrophila Feeding

In the process of co-evolution between plants and phytophagous insects,plants have gradually formed consummate defense measures to resist their natural enemies feeding.Alternanthera philoxeroides is an invasive weed,which distributes widely and seriously harm.Agasicles hygrophila,a host specific flea beetle,is widely used in biological control of A.philoxeroides.In this paper,the volatiles,the changes of defense enzymes and the content of abscisic acid in the leaves of A.philoxeroides were researched in order to explore the defense mechanisms of A.philoxeroides.The result showed that the activities of defense enzymes in A.philoxeroides leaves were not in the same after treated by leaf cutting and the flea beetle feeding about 24 hours.The activities of defense enzyme were closely related to the treatment time and treatment methods.By using dynamic headspace collection,the volatile matters of A.philoxeroides were collected and analysised,which had been fed by different instars of A.hygrophila.The results showed that the relationship between the quantity and content of volatile matters collected from the weed fed by different development stages of A.hygrophila were positive correlation.The number of volatile matters collected from the weed which fed by 1st instar larvae,3rd instar larvae,and adults were 45 species,16 species and 6 species.In the control group of A.philoxeroides,we captured 8 species.The content of ABA in the weed leaves after continued feeding 24 hours by 1st instar larvae,3rd instar larvae and adult of A.hygrophila was determined.The result showed that the ABA content in A.philoxeroides leaves by the flea beetle was higher than the control group.ABA content in the weed leaves fed by 1st instar larvae and 3rd instar larvae was significantly higher than the control group.In conclusion,mechanical damage and insect feeding could induce the increase of defensive enzymes activity in A.philoxeroides leaves.A.philoxeroide fed by A.hygrophila could change the species of volatile substances to response the damage and the content of ABA in leaves was increased.So,responding to mechanical injury and A.hygrophila feeding stress,A.philoxeroide can produce a series of defense response,but the other defense mechanisms,such as the nutrient content in leaves,the changes of secondary metabolites etc.,and the relationship among defense functions remain to be further studied.