Serological characterisation of citrus tristeza virus isolates from Israel

Seven monoclonal antibodies (MAbs) showing homologous reactions with the VT strain of citrus tristeza virus (CTV) were tested against 21 CTV strains or isolates, representing the range of biological diversity and the geographical distribution of CTV in Israel. All the CTV strains gave positive reactions in ELISA with polyclonal antibodies and with one MAb (#25#2). Two MAbs; #13#21 and #3/7 reacted with 19 and 12 out of the 21 CTV strains, respectively. Seventeen CTV strains, including all those previously assigned by sequencing their coat protein gene (CPG) to the CPG-VT group (Mawassi, Gafny & Bar-Joseph, 1993), reacted with five or more MAbs. Four CTV strains of minor epidemiological importance, including two members of the CPG-MT group, did not react with five or more of the MAbs. These results indicated the existence of two serogroups of Israeli CTV strains that can be differentiated by MAbs and which closely correlate with and extend the previous CPG grouping. The extensive biological variation within each CPG group confirms recent analyses suggesting that the CTV pathogenic traits are not necessarily associated with a sequence or antigenic variation of the CTV-CPG.