Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/12/1998
Publication Date: N/A
Interpretive Summary: Numerous isolates of citrus tristeza virus (CTV) have been described. Some are quite mild and do not cause economic injury. Others are very severe and cause a decline in trees grown on sour orange root stocks or stem pitting in sensitive scions irrespective of the rootstock used. It is often important to be able to distinguish mild from harmful isolates, but this has been difficult except by lengthy tests with citrus indicator plants. A serological test has been developed previously that can distinguish mild isolates of CTV from those that cause decline and stem pitting in sweet orange and grapefruit, however, it does not distinguish between decline and stem pitting. This paper describes a serological test that allows rapid identification of CTV isolates that have the potential to induce stem pitting in sweet orange. The discrimination of orange stem pitting isolates of CTV is based on use of specific antibodies in the plate coating step of the ELISA test. This procedure has practical applications for certification and eradication programs, and will also benefit several areas of CTV research.
Technical Abstract: Citrus tristeza virus (CTV) complex produces several economically important diseases. Stem pitting causes substantial losses in many citrus-producing regions of the world. A serological tool to rapidly differentiate stem pitting isolates of CTV was found by evaluating many combinations of trapping and detecting antibodies in an indirect double-antibody sandwich (I-DAS) enzyme-linked immunosorbent assay (ELISA). Two combinations of trapping and detecting antibodies were found suitable for differentiating stem pitting isolates in extracts of infected sweet orange plants. One used a polyclonal serum raised against bacterially expressed CTV coat protein (CP) for trapping and a conformational monoclonal antibody 3E10 for detection, and the other used two polyclonal antisera generated against bacterially expressed CTV CP. Seventy six CTV isolates from 20 countries were analyzed in I-DAS-ELISA using the two different antibody combinations. The 35 isolates associated with stem pitting produced a strong positive signal for CTV isolates. A negative ELISA signal was obtained for those CTV isolates which do not cause stem pitting. Combined use of a universal ELISA format, i.e. one reacting with a broad range of CTV isolates, and a selective ELISA format allowed reliable serological differentiation of CTV isolates which cause stem pitting in sweet orange.