RE SEARCH The new inspections 2 4 Another reason why fewer samples are now necessary is the fact that for virus testing with the former Elisa test more tubers for slowly-germinating varieties were needed. The tubers used to go into the greenhouse first for the necessary seedling assessment. Depending on the variety, sometimes 20 percent of the plants did not emerge in time - or at all. Because enough plants were needed to assess the reliability of the virus test, bigger samples were necessary. Normally, at least two hundred tubers are needed, but for the slowly-germinating varieties double that amount is necessary. The NAK department where NAK staff remove labels and empty sample bags also has less work now. From the 25,000 bags that come in during the 12 weeks after the harvest, the laboratory staff test all the samples for ring or brown rot, plus 18,000 samples for virus, and 5,000 for Erwinia. Before the switch to the new combination test, quarantine samples were processed in a separate place. In the new situation, one joint space has been fitted out, which fully complies with the European quarantine requirements. Thanks to the new analysis method, each tray with a complete sample of tubers can be provided with a sticker for testing for virus, Erwinia and brown and ring rot. 3 When the sample trays have been filled and provided with the necessary sticker or stickers, they move on to the next department. This is the area in which the NAK staff first cut the tops from the tubers to analyse for virus and Erwinia. This is the point where the working method has been drastically changed. Previously, the laboratory staff removed a ball of potato around the top eye. In the new DNA test with PCR, less potato flesh is needed than for the Elisa test. Only a thin slice cut with a potato peeler around the navel end is sufficient. Slightly thicker slices are only necessary from tubers with deep navels. In total, 50 slices in a plastic bag with a clasp are sent to the laboratory. Besides testing for virus and Erwinia, most samples also (or exclusively) need to be tested for brown or ring rot. The laboratory assistants then also remove a small cube at the navel end, which is placed in a separate transparent box with a blue lid. 18 Potato World 2014 • number 1 Pagina 17
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