RE SEARCH Possibility of detecting Erwinia in seed potatoes increased Within the Erwinia Delta Plan, a method has been developed that can reveal the presence of the Erwinias, Pectobacterium, and Dickeya in seed potatoes with more certainty. The improved method uses waste tubers that are removed from the grader and a test which examines the entire tuber. T o show Erwinia in seed potatoes, the NAK (General Inspection Service for Agricultural Seed and Seed Potatoes) examines 4 mixed samples of 50 tubers from every lot. The laboratory technicians cut a slice from the navel ends of each single tuber. After grinding the navel ends, the technicians dilute the extract in a PEB medium, which boosts the growth of the Erwinias. After three days’ incubation under low-oxygen conditions, the DNA is filtered from the extracts. The following step is a test with molecular assays (TaqMan) for the presence of the various Erwinias that can cause bacterial infections. The incubation of the extracts in the growth medium in combination with the TaqMan assays already provide a sensitive test that can be used to reveal many infections. And yet, you still find ‘clean’ lots that develop diseased plants in the field. The main reason for this is the number of tubers in a sample. By testing 200 tubers, infections can only be detected in lots with a relatively high percentage of infected tubers. Testing a bigger sample is not realistic, because this will lead to a big increase in the test costs. To show Erwinia in seed potatoes, the NAK (General Inspection Service for Agricultural Seed and Seed Potatoes) examines 4 mixed samples of 50 tubers from every lot. The laboratory technicians cut a slice from the navel ends of each single tuber. Potato World 2015 • number 1 19 Pagina 18
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