Globally at least 114 virus species are known to be transmitted by whiteflies (family Aleyrodidae). Bemisia tabaci (Bt) transmits 111 of these species while Trialeurodes vaporariorum and T. abutilonia each transmit three species. B. tabaci and T. vaporariorum are present in some areas of the European–Mediterranean region. Of the whiteflytransmitted virus species, 90% belong to the genus Begomovirus (family Geminiviridae), 6% to the genus Crinivirus (family Closteroviridae), and the remaining 4% to the genera Closterovirus (family Closteroviridae), Ipomovirus (family Potyviridae) and Carlavirus (family Flexiviridae). The whitefly-transmitted viruses considered within this project can all cause severe losses to the horticultural industries in the Mediterranean basin and are of quarantine concern to countries within and external to the EU. All are included on the EPPO A2 list, and comprise: Cucurbit yellow stunting disorder virus (CYSDV), genus Crinivirus; Cucumber vein yellowing virus (CVYV), genus Ipomovirus; Tomato chlorosis virus (ToCV) and Tomato infectious chlorosis virus (TICV), genus Crinivirus; and Tomato yellow leaf curl virus (TYLCV), genus Begomovirus. TYLCV is EC listed, and ToCV, TICV, CYSDV and CVYV are on the EPPO Action list. Of the viruses pertaining to this project which have severe affects on tomato crops, Bt transmits TYLCV in a persistent manner and T. vaporariorum transmits TICV and ToCV semi-persistently. ToCV is also transmitted semi-persistently by Bt and T. abutilonia.

The emergence of the polyphagous B biotype of B. tabaci has given whitefly-transmitted viruses a mode to infect new plant species. Bt has been intercepted on traded plant material, for example in a UK interception of Bt carrying TYLCV, and the presence of Bt on traded plant material facilitates global spread of whitefly-transmitted diseases. It is vitally important to equip National Plant Health Service laboratories with appropriate validated diagnostic methods for the detection and identification of whitefly-transmitted viruses of regulatory or quarantine concern to the EU so that any outbreak or interception can be dealt with rapidly and efficiently. The main aim of this collaborative project is the validation of real-time and conventional PCR diagnostic methods for a range of whitefly-transmitted viruses of concern to Europe