81 Validation of Plant Virus Detection A.R. van Schadewijk 1 , E.T.M. Meekes 2 , M. Verbeek 3 and J.Th.J. Verhoeven 4 1 Dutch Flower Bulb Inspection Service, P.O. Box 300, 2160 AH Lisse, The Netherlands 2 Naktuinbouw, P.O. Box 40, 2370 AA Roelofarendsveen, The Netherlands 3 Plant Research International, P.O. Box 69, 6700 AB Wageningen, The Netherlands 4 Plant Protection Service, P.O. Box 9102, 6700 HC Wageningen, The Netherlands Keywords: accreditation, performance characteristics, ELISA, PCR Abstract Validation of test methods is required for laboratories seeking ISO 17025 accreditation. Recently developed manuals help choosing relevant performance characteristics to be studied for qualitative tests common in plant virus detection. For routine testing in certification schemes additional information on the plant material is important to determine the scope of the accredited application. For application of virus tests for diagnostic purposes the determination of certain performance charac- teristics is highly recommended. Furthermore, in case of detection of quarantine organisms a confirmation by an alternative test is indispensable. INTRODUCTION Testing for plant viruses includes making decisions. Stocks are classified, candidate plants are selected and ship loads of plants may be destroyed based on test results. Tests are performed to the best of our knowledge but this is not always enough. Using test kits and protocols from established suppliers does not release us from the responsibility to check the quality of the assays. Validation is the key word for many laboratories seeking accreditation or extending the number of tests under the present accreditation. However, also for laboratories without accreditation validation becomes common practice. Validation means proving that the method is fit for the purpose we have in mind. Plant Research International (PRI), assisted by a panel of Dutch plant pathologists, published a manual for validation of plant pathogen tests (Van der Vlugt et al., 2006; see also ISO/IEC 17025). This manual describes performance characteristics that are important for qualitative assays and includes examples on how to obtain data. However, once aspects like detection limit, trueness, selectivity, specificity, repeatability, reproducibility, robustness etc. are determined, we realize that a report describing these facts is not complete without technical information. Plants are a difficult matrix for virus detection and occasionally evoke peculiar interactions with plant pathogens or components of the diagnostic assay. The successful detection of viruses in plants depends on season, distribution in plants, storage conditions and geographical distribution with possible false negatives. The plant material itself may cause false positives. Antibodies may fail to detect all serotypes and primers may not cover the whole range of strains. Information on these processes and characteristics is needed before we can define the test protocol, the quality of the assay, and its boundaries, in terms of season, type of plant material to be sampled etc. VALIDATION OF TEST METHODS Validation is defined as the process of checking if a test method is suited for its intended purpose. Before starting a process of validation it is necessary to determine:  The purpose of the test, test method and matrix.  Whether the test is quantitative or qualitative.  Which performance characteristics need to be determined. Proc. XII th IS on Virus Diseases of Ornamental Plants Eds.: A.F.L.M. Derks et al. Acta Hort. 901, ISHS 2011