Preliminary Study On The Distribution Of Citrus Tristeza Virus In Toxoptera Citricida

Tristeza caused by Citrus tristeza virus (CTV) is an economically important citrus disease, which is spread mainly by aphids and grafting. Various isolates of CTV and the most efficient vector brown citrus aphid (Toxoptera citricida Kirkaldy) are widely distributed in China. In the past years, some superior cultivars of pummelo, sweet orange and mandarin hybrid have been developed to some extent in China, as the result, stem-pitting tristeza problem on pummelos and some susceptible cultivars of sweet oranges become serious since mid-1990s'. So far, according to the experience obtained in developed countries, mild strain cross protection (MSCP) has been proved to be the most effective way to control this problem where severe CTV isolates and brown citrus aphids co-exist. However T. citricida has recently spread to Caribbean, Central America and Florida, breaking down cross protection in grapefruits and sweet oranges.So far, very little is known on the mechanisms of the specific CTV-aphid interaction. Previous studies showed that citrus variety, CTV isolate and environment could influence the aphid transmissibility. And now people found that CTV isolates were detected in single T. citricida with frequency of 63.3%-91.1% and 71.1%-91.1% by RT-Nested-PCR and Real-Time RT-PCR, respectively. And more copies of CTV-targets were detected in single viruliferous T. citricida individuals that acquired high transmissibility CTV isolates. In this study,6 CTV isolates were segregated by the single aphid transmission, and RT-Nested-PCR was used to detect CTV isolates in the single T. citricida, and the stylet, head or abdomen of T. citricida. Furthermore, fluorescence antibody labelling was used to locate CTV in T. citricida. The following results have been achieved:The single aphid transmission rate of 6 different CTV isolates ranged from 0% to 47.5%.The average transmission rate of severe and mild CTV isolates was 21.25% and 12.92%, respectively, but this difference was not statistically significant.After 24 h acquisition access period,4 CTV isolates were detected in single T. citricida with frequency of 72.65%～90% by RT-Nested-PCR.No significant difference was found between the precentage of viruliferous tissues of T. citricida that acquired CT77 or CT30. Furthermore the positive rate of CTV is highest in the stylet, following is head and abdomen.CTV was uneven distributed in the stylet of T. citricida by fluorescence antibody labelling. And CTV could be detected in the middle of stylet and the stylet tip.