| Sumario: | In Colombia the occurrence of CTV infected trees showing decline and stem pitting was reported since 1940; and later reports indicated the presence of Toxoptera citricida (Kirkaldi) an efficient vector of severe strains of the virus. This paper describes results from a 3-year study whose objective was to build a collection of CTV isolates from different regions of Colombia, characterize it by serological and biological procedures, and to identify mild virus isolates for testing in cross protection studies. 139 field isolates were collected from citrus orchards in eight department (Valle del Cauca, Quindlo, Risaralda, Cundinamarca, Tolima, Atlántico, Meta and Magdalena). The samples were analyzed with the polyclonal antiserum IgG CTV and the specific monoclonal antibody MCA13, to determine the presence of virus particles and the virulence profile of the strains. In order to determine the biological severity of these field isolates, they were grafted onto virus-free Mexican lime seedlings which were grown inside an aphid- proof screenhouse, and evaluated for CTV symptoms (including vein- clearing, vein corking, epinasty and stem pitting). Over 95% of the samples from all the regions were infected by the virus. When analyzed with the MCA13 monoclonal antibody, all samples from six out of the eight sates reacted positive, approximately 24% of the isolates from Quindio and Risaralda were negative for this severe strain- specific antibody. Only three isolates out of 130 failed to induce severe CTV symptoms on Mexican lime and gave negative reaction with the MCA13 monoclonal antibody. These isolates may be potential donors of mild strains which could be useful in cross protection studies.
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