A Preliminary Study Of Citrus Tristeza Virus Acquisition And Transmission By Diaphorina Citri

Citrus tristeza virus(CTV)is one of the most important viruses of citrus trees,which is primarily reported as a graft transmissible virus and also vectored by several aphids.Citrus tristeza caused by CTV is preverent in the field.Some CTV-positive plants show stem pitting,seedling yellows and quick decline after being affected.The Asian citrus psyllid is the important pests of agricultural production,which can transmits Huanglongbing.In the present study,samples from different citrus varieties and some phloem-sap sucking insects from several orchards of different provinces were collected and the presence of CTV within them were detected with RT-PCR.This paper first proposed that psyllid can transmit CTV to healthy plants.After confirming that psyllids were CTV-positive,orange jasmine(Murraya paniculata(L.)Jack),‘Shatangju’ mandarin plants,‘Eureka’ lemon(C.Limon(L.)Burm.F.)seedlings,and pomelo plants were further used to study the CTV acquisition,persistence and transmission by D.citri.The result were as follows:1.CTV orchard surveys: CTV was commonly occurred in citrus orchards and some sap-sucking insects in the field.The insidence of CTV-positive citrus trees in six orchards were 20 %-100 %.For the presence of CTV in the sap-sucking citrus psyllids,cochineals,or mealybugs were 92 % to 100 %.However,the whiteflies were found CTV-negative.2.D.citri can acquire CTV from CTV-positive ‘Shatangju’ mandarin plants.Acquisition of CTV by D.citri was highest(85 %).3.Percentages of CTV-bearing adults and CTV titers within them did not differ significantly among the 0,5 and 15-day assessments after the adults were transferred to CTV-negative ‘Shatangju’ mandarin and persist the CTV for at least 15 days.RT-PCR indicated that 72 % and 65 % of D.citri remained CTV-bearing after 5 and 15 days.In contrast,percentages of CTV-bearing adults and estimated CTV titers within them,after the adults were placed on CTV-negative orange jasmine plants decreased significantly 5 and 15 days after the acquisition access period.4.Transmission of CTV by D.citri to mandarin,lemon,and pummelo plants.The percentage of CTV-positive plants were screened using 9 ‘Shatangju’ mandarin plants,6‘Eureka’ lemon plants,3 ‘Miyu’ Pummelo and 3 ‘Shatian’ pomelo respectively,after 5days of exposure to groups of 10 CTV-bearing D.citri.After 120 days Inoculation Access Period(IAP),66.67 %,83.33 %,100 % and 100 % of the ‘Shatangju’ mandarin,‘Eureka’ lemon,‘Miyu’ pummelo,and ‘Shatian’ pomelo plants were CTV-positive respectively.5.CTV transmission by grafting the CTV-positive scions and D.citri.120-day after graft inoculation,100 % of the lemon plants were CTV-positive.Comparatively,transmission of CTV by D.citri was somewhat slower or less efficient,with 66.67 % plants were CTV-positive.In summary,this study demonstrated that Citrus tristeza disease is widely distributed in the field.The Asian citrus psyllid can acquire CTV with a relatively high efficiency and is capable of transmitting the virus to healthy ‘Shatangju’ mandarin and ‘Eureka’ lemon trees,‘Miyu’ pummelo,and ‘Shatian’ pomelo plants but not to orange jasmine trees.Therefore,this study establishes that D.citri can transmit CTV as well as CLas.This finding could be important in citrus crop management.Possible interactions between the two pathogens inside the vector insect and host are also interesting matters pending investigation.