Studies On The Transmission Characteristics Of Tomato Chlorosis Virus By Bemisia Tabaci Q And Transcriptomic Analysis

The whitefly Bemisia tabaci is an important invasive agricultural pest in China.It chiefly inflicts damage by direct feeding,secreting honeydew that triggers sooty mold and transmitting plant viruses.In recent years,Tomato chlorosis virus(ToCV),which is transmitted by B.tabaci,has become an important new virus in tomato production.It has been outbreak in the tomato planting areas in China,causing serious economic losses.In this study,we systematically investigated the relationships between the population of B.tabaci and occurrence of ToCV in the field,studied the effects of different infection modes of ToCV and Tomato yellow leaf curl virus(TYLCV)and insecticides on the transmission of ToCV by B.tabaci,and utilized RNA-Seq technology to analyze genes differentially expressed of B.tabaci after infected by ToCV.Results provided scientific basis for effective control and prevention of virus diseases and B.tabaci.The main results are as follows:1.Through systematic field surveys,it was found that ToCV could be effectively transmitted by B.tabaci,and incidence rate of ToCV increased with the increase of the population of B.tabaci.Co-infections of ToCV and TYLCV occurred widely in different resistant TYLCV varieties of tomato,and co-infection rates of some varieties were 90%.Besides,two viruses were detected in B.tabaci collected from 5 vegetable producing areas in Shandong Province,and the virus carrying rate increased year by year.2.Co-infection of ToCV and TYLCV significantly increased the transmission efficiency of B.tabaci to ToCV.Compared with single infection,the virus acquisition efficiency of B.tabaci had increased by 45%,and the transmission rate had increased by 12% under co-infection.Co-infection had increased the accumulation of ToCV in tomato.The peak period of ToCV increment occurred at 14 d after inoculation in the single infection mode,and the peak period of ToCV increment occurred at 21 d after inoculation under co-infection mode.Studies showed that ToCV and TYLCV might have antagonistic effects in the early stage of mixed infection,and synergistic effect in the late stage.3.Virulence test showed that the sensitivity of ToCV-infected B.tabaci to thiamethoxam and spirotetramat decreased significantly.The sublethal effect of insecticide had no significant effect on virus acquisition efficiency of B.tabaci(P > 0.05),but it significantly increased the transmission efficiency of B.tabaci to ToCV(P < 0.05).ToCV-free B.tabaci preferred to settle on ToCV-infected tomato plants,while ToCV-infected B.tabaci preferred to settle on ToCV-free tomato plants.After being treated with insecticides,ToCV-free B.tabaci still preferred ToCV-infected tomato plants,while ToCV-infected B.tabaci showed different choices.After sublethal concentration of spirotetramat,ToCV-infected B.tabaci preferred tomato plants infected by ToCV.After being treated with thiamethoxam,ToCV-infected B.tabaci preferred to choose healthy tomato plants.Therefore,simultaneous presence of insecticides and viral factors would increase the risk of virus transmission in the field.4.RNA-Seq technology was used to obtain transcriptome sequencing datas of B.tabaci fed on ToCV-infected tomato after 6,12,24 and 48 h.DEG analysis showed that a large number of genes were differentially expressed at 4 feeding time points,and the 24 h feeding time points was the peak of gene differentially regulated.Further analysis was obtained that the differentially expressed genes were mainly related to signal transduction,receptors,lysosomes and apoptosis.GO analysis revealed that ToCV caused abnormal expression of a large number of genes in B.tabaci,resulting in a series of functional changes.The function in the early stage of infection is mainly concentrated in signal transduction,transmembrane transport,autophagy and enzyme activity.In the late stage of infection,The function was mainly concentrated in ribosome formation,transmembrane transport,redox and so on.KEGG analysis showed that ToCV induced the significant enrichment of metabolism,signal transduction,transport and catabolism pathway,lysosome pathway in B.tabaci.