Biological and molecular characterization of Uruguayan citrus tristeza virus field isolates

Citrus tristeza virus (CTV) is the causal agent of the most important viral disease of citrus. Symptoms that may affect the productive potential of citrus plants are observed in Uruguayan orchards even though resistant rootstocks are used. CTV is fully eliminated in propagative materials by the National Sanitation and Certification Program, but since the virus and its vector are widespread in the country, the risk of infection in the field persists. In this situation, using mild CTV strains in a cross-protection program would be a useful alternative to attempt to increase yield and quality of the local citrus industry. To this aim, this study assessed the biological and molecular characteristics of 32 local CTV isolates. Bioassays were conducted in a greenhouse with controlled conditions. Each isolate was graft-inoculated on Mexican lime, sweet orange, sour orange and Duncan grapefruit indicator plants. Symptoms and their intensity were evaluated. Molecular characterization was carried out by RT-PCR amplification, using primers for the p25, p20 and p23 genes. PCR products were sequenced, nucleotide sequences were aligned with international reference strains and phylogenetic trees were constructed. Results of the biological and molecular analysis showed the prevalence of severe CTV isolates with a high genetic variability. Two out of 32 characterized isolates were selected as mild CTV isolates to be tested as candidates for future cross-protection experiments. The survey showed a complex scenario for the management of CTV in Uruguay.