RE SEARCH Possibility of detecting Erwinia in seed potatoes increased From each lot in the new test, ten mixed samples of 20 tubers were tested by grinding the navel end of each tuber and incubating this in the PEB medium. tuber. In the study, ten sub-samples of 20 tubers in plastic bags with some moisture were placed under vacuum conditions. These are circumstances in which Erwinias flourish, but many other bacteria die off. After seven days of incubation at room temperature, the laboratory technicians collected the moisture from the plastic bags. They isolated the DNA and then carried out the test with the TaqMan assays. The researchers found considerably more infections in the samples with the whole tubers than in the samples with the navel ends. When you use the whole waste tubers instead of the navel ends of random samples, you find approx. 10 times more infections. Using the improved method reduces the risk that a lot is wrongly declared Erwinia-free. Test available for trade and cultivation The test is not directly usable in the regular inspection system of the NAK. From the 200 tubers the inspector collects, only the sliced navel end is available for the Erwinia test. The laboratory technicians use the remaining part of the tuber for testing other pathogens such brown rot, ring rot and viruses. Furthermore, it is difficult for the NAK to standardise the collection of waste tubers. The test can be used, however, by trading companies to offer the grower more certainty about the absence of Erwinia bacteria in a lot of seed. But this new test does not offer absolute certainty either, because the random sample of 200 tubers is too small for that. ● You still find ‘clean’ lots that develop diseased plants in the field. The main reason for this the number of tubers in a sample. Jan van der Wolf Potato World 2015 • number 1 21 Pagina 20
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