Epitope Diversity of Citrus Tristeza Virus Isolates in Spain

Abstract

Fifty-nine Spanish citrus tristeza virus (CTV) isolates from the IVIA collection were tested against nine CTV-specific monoclonal antibodies (MCAs) by double antibody sandwich indirect ELISA (ELISA-DASI). Six different epitopes were detected, and seven distinct serogroups were defined by their reaction pattern with the different MCAs. Five of the MCAs recognized all Spanish CTV sources tested. Changes in epitope composition, observed in someisolates after aphid transmission or after propagation in certain hosts and graft transmission, indicated that some field isolates are mixtures of strains. The analysis of 1,613 CTV-infected trees collected from areas with variable CTV incidence showed that up to 18% of the samples from trees in heavily infested areas (>80% incidence) reacted with all MCAs, whereas all samples from areas with less than 2% CTV incidence failed to react with some MCAs. This suggests that mixtures of strains are more abundant in areas where CTV has been established for a long time. The analysis of 3,231 CTV-infected trees by ELISA-DAS with MCAs 3DF1,3CA5, and MC13 showed that only 8.7% reacted with MCl3, whereas 99.6 %reacted with 3DF1 and 100% with 3CA5. A mixture of 3DF1 and 3CA5 detected all isolates. Under Spanish conditions, the reaction with MC13 was not correlated with the decline of trees on sour orange in the field. However, all known severe strains reacted with MC13 and 10E3 antibodies.