| Tristeza caused by citrus tristeza virus(CTV),is an important citrus virus disease.CTV can be transmitted by aphids in semipersistent manner,in addition to graft.The brown citrus aphid(Toxoptera citricida,Kirkaldy)has been recognized as one of the most effective insect vector of CTV.The wide distribution of CTV virulent strains and brown citrus aphid in China,seriously threatens the production of orange and pomelo varieties.In the tripartite interaction of plant-virus-vector,not only can the virus directly affect the insects by remaining in the insects' body,but also by triggering the stress response of host plants,thereby affecting the insect to some extent.Both manners will affect the ecological adaptability of insect.The tripartite interaction is rather complex,specific and is closely related to the way of transmission by vector.The systematic study on these relationships will contribute to the development of new strategy for management of plant virus disease.and further provide novel ideas for the control of insect pests and breed insect resistant plants.In this study,the interaction of brown citrus aphid-citrus sinensis-CTV was investigated.By using technology of electrical penetration graph,chromatograph-mass spectrometer-computer and RT-q PCR,we compared the biological characteristic of brown citrus aphid on infected plants,such as development,host selection,feeding behavior,etc.Also,we analysized the effect of CTV-infection and/or brown citrus aphid-infestation on host plants,including the content and composition of free amino acids,sugars content,defensive enzyme activity and concentration of salicylic acid(SA),jasmonic acid(JA)and ethylene(ET).Besides,we evaluation the brown citrus aphid's host selection,population growth and feeding behavior on SA or JA treated plants,in a bid to provide a theoretical basis for the tripartite interaction.Main results are as follows:1.The developmental period of brown citrus aphid had been prolonged 23 %,5 %,3 % on CT14,CT16-2,CTLijian infected plants,respectively.The duration of third and forth instar nymphs of brown citrus aphid were for 2.38 ± 0.43 d,1.92 ± 0.19 d on CT14 isolate,which was significantly longer than that on the healthy plants for 1.29 ± 0.26 d and 1.50 ± 0.01 d.Brown citrus aphid's population growth was significantly inhibited when feeding on CTV infected plants.The population size reached to 106.47 ± 17.27,124.33 ± 11.78,155.60 ± 8.90 from 6 adults when feeding on CT14,CT16-2 and CTLijian plants,respectively,which is significantly lower than that on healthy plants,for 175.69 ± 11.32.2.The host selection of brown citrus aphid was compared on healthy and infected plants.Within 2 h,CTV-infected plants attract more aphids;over time,this attractiveness was decreased,aphids rapidly emigrated from infected plants to healthy plants.There were no significant differences in aphid rates among the treatments after 5 h.3.CTV infection significantly changed brown citrus aphid's probing behavior.It became shorter and more frequently on infected plants before the phloem probing.The total duration of E of brown citrus aphid on CT14,CT16-2 and CTLijian isolate plant was for 260.35 ± 29.55 min,224.95 ± 24.96 min,213.91 ± 24.08 min,respectively,which were obviously longer than that on healthy plant for 132.69 ± 23.60 min.Hence,the probability of virus acquisition and transmission would be enhanced when brown citrus aphid fed on CTV-infected plants.4.CTV-infected plants excreted comparatively a lower proportion of free amino acids,especially for essential amino acids.Meanwhile,a higher or unchanged level of sugars was showed in infected plants,thus resulting in the higher ratio of simple carbohydrates to amino acids.While the quality did not change significantly following aphids infestation.Besides,relative to uninfested plants,CTV-infection and/or brown citrus aphid-infestation significantly altered defensive enzyme activity of catalase(CAT),superoxide dismutase(SOD),phenylalanine ammonia-lyase(PAL)and polyphenol oxidase(PPO).In the case of peroxidase(POD),it's only relative to aphids infestation,which indicating that thenutritional composition may play an important role in feeding behavior and population growth of brown citrus aphid.5.We quantified the SA,JA and ET in plant that were infested with CTV infection and/or aphids infestation.SA content was significantly higher in plants infested with CT14 or CT16-2,while the ET content was significantly decreased and the JA content was little decreased,but not significantly.6.BGL2,PR1(the regulation gene of SA-pathway)and PAL(SA-biosynthesis genes)were significantly up-regulated in CT14,CT16-2 and CTLijian isolate,while LOX2(the upstream gene of JA-pathway)and MYC2(the downstream gene of JA)were down-regulated in infection plants.Besides,JA suppressor gene,JAZ were up-regulated in the three CTV isolates,though the JA-biosynthesis gene,FAD3 did not change significantly.The key metabolism genes of ET,ACO,ACS,ETR,EBF were down-regulated in three CTV isolates.7.Exogenously applied plant defense signals SA and JA on citrus sinensis had significant effects on performance of brown citrus aphid.The population size reached to 78.89 ± 7.69 and 96.72 ± 10.03 from 6 adults on SA/JA-treated plants,respectively,which was significantly lower than that of mock plants for 175 ± 15.31.Aphids preferred to control plants when compared with SA or JA-treated plants.We also found that aphid's probing behavior as well as duration time of E wave became more frequently and longer on SA-treated plants.The effect of exogenous SA-treatment on brown citrus aphid's growth was consistent with the indirect effect induced by CTV infection,indicating that the increase content of SA in infected plants may be one of the important factors for aphids population growth. |
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