SEROLOGICAL DIFFERENTIATION OF THE CITRUS TRISTEZA VIRUS ISOLATES CAUSING STEM FITTING IN SWEET ORANGE

Citrus tristeza virus (CTV) complex comprises a number of isolates or strains producing several economically important disease syndromes in commercial Citrus sop. The stem pitting syndrome is the most important , and causes substantial losses in many citrus-producing regions of th e world. In an attempt to develop a serological tool to rapidly differ entiate stem pitting isolates of CTV, we evaluated many combinations o f trapping and detecting antibodies in an indirect double-antibody san dwich (I-DAS) enzyme-linked immunosorbent assay (ELISA). Two combinati ons of trapping and detecting antibodies were found suitable for diffe rentiating stem pitting isolates in extracts of infected sweet orange plants. One used a polyclonal serum raised against bacterially express ed CTV coat protein (CP) for trapping and a conformational monoclonal antibody 3E10 for detection, and the other used two polyclonal antiser a generated against bacterially expressed CTV CP. Seventy-six CTV isol ates from 20 countries, including 35 that cause stem pitting in sweet orange plants, were analyzed in I-DAS-ELISA using different combinatio ns of polyclonal and monoclonal antibodies for trapping and as interme diate detecting antibodies. The ELISA format developed produces a stro ng positive signal for CTV isolates that cause stem pitting in sweet o range plants and a negative ELISA signal for CTV isolates that do not cause stem pitting. When combined with data on a universal ELISA forma t, i.e., reacting with a broad range of CTV isolates, these selective ELISA formats allowed reliable serological differentiation of CTV isol ates that caused stem pitting in infected sweet orange plants.