Inter-laboratory evaluation of a duplex RT-PCR method using crude extracts for the simultaneous detection of Prune dwarf virus and Prunus necrotic ringspot virus

The operational capacity of a duplex RT-PCR method for simultaneous detection of PDV and PNRSV has been established by nune European laboratories. A total of 576 samples from Prunus trees with known sanitary status, corresponding to 32 samples in two repetitions for each laboratory, were analysed. The level of sensitivity achieved by the method was 98.3% for PDV and 90.4% for PNRSV. The unilateral 95% confidence intervals were calculated for all these values. Cohen’s Kappa coefficient of repeatability and reproducibility of the technique indicated a strong agreement between data. Likelihood ratios were 7.50 (positive) and 0.02 (negative) for PDV. Foer PNRSV the positive likelihood ratio was 15.00 while the negative likelihhod ratio was 0.11. in addition post-test probabilities of infections were calculated to manage the risk associated with the routine use of this method. This allows an accurate test result interpretation to facilitate the integration of this new technique into a certification scheme.