Plum pox potyvirus (PPV) isolates may be divided into four groups separated by serological, molecular, and epidemiological differences. Monoclonal antibodies specific for the two major groups of isolates, represented by the D and M serotypes of the virus, have been obtained. Polymerase chain reaction (PCR)-based assays allowing the direct detection and differentiation of PPV isolates have also been developed. We now report on a large-scale comparison of these two typing approaches. The results obtained show an overall excellent correlation between the results obtained in indirect double-antibody sandwich enzyme-linked immunosorbent assay using PPV-D- and PPV-M-specific monoclonal antibodies and those derived from either specific PCR assays or restriction fragment length polymorphism analysis of PCR fragments. Without exception, all isolates reacting positively with the PPV-M-specific monoclonal antibody were found to belong to the M serotype using the PCR-based assays, while 51 out of 53 isolates recognized by the D-specific monoclonal antibodies belonged to the D serotype according to the PCR typing results. However, failure to react with a specific monoclonal antibody did not prove as effective a predictor of the serotype of the isolate analyzed. In a few cases, the results obtained with the various techniques diverged, indicating low level variability of the epitopes recognized by the serotype-specific monoclonal antibodies. Isolates belonging to the two minor groups of PPV (El Amar and Cherry) also gave divergent results, indicating that the current typing assays are not suited for the analysis of such isolates.
We have developed an immunocapture‐PCR (IC‐PCR) detection technique for plum pox potyvirus (PPV) which is both simple and highly sensitive. This single‐day assay can detect about 2000 virus particles (200 fg of virus) diluted in 100 μl of crude plant sap, which is equivalent to a sensitivity about 2000 times better than that of a standard ELISA assay. RFLP analysis and sequencing of the amplified cDNA fragment indicate that three groups of strains with limited intra‐group variability can be discriminated. Two of these groups correspond to the previously described D and M serotypes of PPV. The third group contains, so far, only the El Amar Egyptian isolate. Strains belonging to the D or M serotypes can easily be discriminated by Rsal polymorphism in the amplified cDNA fragment. Synthetic oligonucleotides allowing specific amplification of PPV strains belonging either to the D or to the M serotypes have also be designed.
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