Booster immunization with a partially purified citrus tristeza virus (CTV) preparation after priming with recombinant CTV coat protein enhances the binding capacity of capture antibodies by ELISA

Serological Detection of Citrus tristeza virus with Antibodies Developed to the Recombinant Coat Protein

Antibodies specific for the recombinant coat protein (rCP) of the p25 gene of Citrus tristeza virus (CTV) were developed in goats and rabbits and further evaluated as a complete kit for the detection of the virus using healthy and CTV-infected tissue. The combination of goat T1 used as primary (coating) and rabbit C3 as intermediate (detecting) rCP antibodies reacted efficiently, with optical density at 405 nm (OD₄₀₅) values between 0.250 and 2.000 with samples from an international collection of diverse CTV isolates. The CTV isolates tested cause a broad spectrum of disease syndromes in different citrus hosts. The OD₄₀₅ values for healthy tissue were less than 0.100. Likewise, the combination of goat T1 and rabbit C3 rCP antibodies gave consistent results for CTV-positive and -negative sample discrimination when directly compared with the Central California Tristeza Eradication Agency (CCTEA) antibodies used for large-scale CTV detection and a commercially available CTV serological detection kit. The combination of goat T1 and rabbit C3 rCP antibodies showed its suitability for large-scale indexing with samples collected in commercial groves as part of the CCTEA's regular monitoring program. The evaluation included 41,195 samples from 301 commercial groves from districts 1, 2, and 3. In total, 26 trees (0.063%) were found to be CTV positive using the T1/C3 rCP antibody combination. Results of this research provide evidence that rCP antibodies can be efficiently used for both capturing and detecting CTV antigens in double-antibody sandwich indirect enzyme-linked immunosorbent assay.

D-RNA molecules associated with subisolates of the VT strain of citrus tristeza virus which induce different seedling-yellows reactions

Citrus tristeza virus (CTV) strains were previously catalogued as seedling-yellows (SY) and non-SY (nSY) types, according to their yellowing and stunting effects on indicator seedlings. Among subisolates of the VT strain, which were selected from chronically infected Alemow plants, there was a correlation between the presence of 2.4-, 2.7- and 4.5-kb D-RNAs, and SY and nSY reactions, respectively. Similarly, plants infected with Mor-T subisolates, which cause SY, contained D-RNAs of 2.6 to 2.8 kb, while nSY subisolates from recovered sour orange tissue contained a major D-RNA of 5.1 kb. Plants harboring the 2.7-kb D-RNA were protected against challenge inoculation with a subisolate harboring the 4.5-kb D-RNA. This study suggests that the nSY reaction results either from the absence of SY gene(s) in the genomes of certain CTV strains or through the suppression of the effects of SY gene(s) by D-RNAs with 5' parts larger than 4000nt.