RE S EARCH Post-checks step by step To produce evidence of infection with a virus that is no longer visible in the field, all seed potatoes have for many years been sent to the Dutch General Inspection Service for Agricultural Seed and Seed Potatoes (NAK) for post-checks. This is necessary because, unlike man and animal, a plant cannot recover from a virus infection. After infection, the yield and quality are negatively influenced, and this is itself reason to keep the seed free from these harmful micro-organisms. In addition to inspection in the field, the post-checks of the Dutch General Inspection Service for Agricultural Seed and Seed Potatoes (NAK) ensure that the quality of Dutch seed remains at a high level in terms of health. The organisation tests around 3 million tubers every year. This means that during the busiest season, 70,000 to 80,000 tubers are being processed every day. Since one to two hundred tubers are usually being processed per sample, this means around two to three thousand results each week. The permanent committee of the NAK determines the haulm destruction dates on the basis of aphid catches. Moreover, the committee also determines the post-check policy. Post-checks are always obligatory for the higher S and SE categories. For the E, A and C categories, exemption of postchecking is given if the foliage has been destroyed before the haulm destruction date, but this depends on the year. Post-checking is also obligatory for these categories if the foliage is going to be destroyed after the haulm destruction date, because then the tubers could be susceptible to a virus infection. The haulm destruction date is determined on the basis of the number of aphids and the presence of a virus infection in any particular year. As soon as the aphids start flying, it usually takes 10 to 14 days before virus Y, which causes the most problems, reaches the tubers. Since the nursery plants have been visually inspected, a great deal has improved with regard to the reliability of the post-checks. The long waiting period before test results are known is also a thorn in the flesh of the NAK. If a reliable and reasonably priced test were to become available, so that the NAK could check the tuber itself, the problem would be solved. But test methods that would make that possible are either far too expensive or of questionable reliability. ● Jaap Delleman 1 Staff are processing 33 million tubers in great concentration 2 Tracking and Tracing starts when the potatoes are accepted 3 Every lot is kept apart carefully 4 For the S and E categories testing is always necessary 11 Scanning to know where each lot is 10 Each topeye has its own place 12 And then into the glasshouse to grow. Urgent lots get a red label 18 Four stems in one tube 19 Turn the leaf and clean with water from the tap 12 Potatoworld 2006 Pagina 11

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