Characterization of isolates of Citrus tristeza virus by sequential analyses of enzyme immunoassays and capillary electrophoresis-single-strand conformation polymorphisms.

Citrus tristeza virus (CTV) is the causal agent of tristeza disease, which is one of the most devastating diseases of citrus crops worldwide. This paper describes a method for the rapid detection and genotyping of naturally spreading CTV isolates. This method uses ELISA or dot-blot immunological tests to detect trees infected with CTV. The reaction wells or membrane spots for which there is a positive reaction are sequentially treated by (i) washing and elution of viral RNA from the trapped samples, (ii) one-step synthesis of cDNA and PCR and (iii) automated fluorescence-based capillary electrophoresis single-strand conformation polymorphism (CE-SSCP) analysis of amplification products. Comparative CE-SSCP results are presented for CTV RNA extracted directly from infected leaves and ELISA plates or from membranes. In the analyses of all of these RNA samples, the p18, p27 and p23 CTV genes were targeted for amplification. Specific profiles of forward and reverse strands were obtained from a group of eight CTV isolates collected in Sicily, each with distinct biological characteristics, which were analyzed using the conventional two-step procedure (immunological detection followed by CE-SSCP molecular characterization after RNA isolation) or in a continuous process of ELISA/CE-SSCP or dot-blot/CE-SSCP starting from infected plant material. The combined method is simple, highly sensitive and reproducible, thus allowing the processing of numerous field samples for a variety of epidemiological needs. The sequential processing of an ELISA or dot-blot/ELISA followed by CE-SSCP is expected to allow the rapid detection of recent CTV infections along with the simultaneous characterization of the genetic diversity and structure of the population of newly invading CTV.