Preliminary molecular characterization of some Citrus tristeza Closterovirus isolates infecting Croatian citrus

Citrus tristeza Closterovirus (CTV) is widespread in major citrus-growing regions of the world often causing destructive diseases. Citrus samples were taken from orchards in the Croatian coastal region. CTV was detected in two symptomless field trees of Satsuma mandarins and one diseased lemon tree. Double-stranded RNA was isolated from the field trees and the dsRNA patterns were compared in polyacrylamide gels. The same dsRNA extracts were used as templates in RT-PCR experiments amplifying the CTV coat protein sequence. Amplicons were subjected to SSCP and RFLP analyses. The results indicate greater similarity between CTV isolates from Satsuma mandarins than between these two and the lemon isolate.

Prospects of classical cross protection technique against Citrus tristeza closterovirus in Pakistan: A review

In Pakistan citrus groves in general are facing a serious problem of decline that is attributed to different causes. The major cause, however, is the prevalence of citrus virus and virus-like diseases; Citrus tristeza virus (CTV) is of utmost concern. Although CTV has been identified and characterized on the basis of serological and physical properties, no information is available on the strains of CTV in Pakistan. The identification of CTV strains will be helpful in developing strategies to control the decline of citrus trees to a great extent. Many citrus growing countries have successfully used the technique of cross protection to minimize the drastic effect of severe CTV strains. By pre-immunization of the citrus tree with mild strains, the decline can be controlled to increase the life span of the citrus tree. In this study we focus on the possibility of establishing a cross protection technique in Pakistan against the CTV strains.  

080 Genetic Transformation of Grapefruit (Citrus paradisi) and Sweet Orange (C. sinensis) With the Coat Protein Gene of CTV

Citrus Tristeza Closterovirus (CTV) induces mild and/or severe symptoms on Citrus species. It may cause death of trees if the rootstock-scion combination is susceptible. It has been found in other plant/virus combinations that transformation with partial or complete viral genes (e.g., coat protein genes) can confer resistance to the resulting transgenic plants. We previously reported A. tumefaciens mediated transformation and production of two sour orange (C. aurantium L.) plants expressing the coat protein gene of CTV, which was the first report of production of transgenic Citrus using a viral gene. However, in order to properly evaluate resistance, it is necessary to obtain as many transgenic Citrus plants from single transformation events as possible. Therefore, we are currently transforming grapefruit (Citrus paradisi) `Marsh' and `Star Ruby' and sweet orange (C. sinensis) `Valencia' with CTV coat protein genes. These species are susceptible to CTV and more amenable to transformation than sour orange. Epicotyl segments of etiolated seedlings were inoculated with A. tumefaciens strain EHA101 harboring binary plasmid pGA482GG containing the coat protein gene of mild Florida CTV strain T30 (CP-T30) or severe Florida strain T36 (CP-T36). Putatively transformed shoots were regenerated on selection medium containing kanamycin. Regenerated shoots were evaluated with GUS assays; those shoots positively identified by GUS were then evaluated with PCR. We have currently identified 17 `Marsh' grapefruit, 20 `Star Ruby' grapefruit, and seven sweet orange putatively transformed plants.