RE SEARCH Bacteria project completed? regarding the entire Erwinia issue, contamination being just one of them’, was the reaction of Henk Velvis of HZPC R&D, who was one of the researchers closely involved in the project. ‘We expected that the wide range of cropping information in this section, linked to analyses in affiliated lots, would give us leads to any possible cause for initial contamination. At that stage, it seemed quite a logical thought. Accurately monitoring the entire cultivation process at farm level, including all sampling and analysing, is a gigantic task. In view of all other questions that needed answering, this was far too much for only one fulltime researcher. Erwinia cannot survive in soil (figure 01) What has been successful, though, is that a few risk factors that may play a role in initial infections have been mapped out. This was done with field trials and experiments in the greenhouse. These showed that Erwinia cannot survive in soil. It does not seem probable at this stage that potato plants can contract an Erwinia infection through Erwinia from an earlier crop, say project members. During the growing season, contamination from whatever source can infect a clean crop via damaged stems and via entire or damaged roots. It is also possible that the groundwater is instrumental in spreading bacteria over the plot. At least it is clear now what risks there are of contamination. Further research is necessary into the role of these risk factors in contamination in the field, and into the origin of the infections. Only when that is clear, can growers start taking immediate action, concludes the project group. Spreading in the soil is possible While studying contamination and the population structure of Erwinia in the past four years, a number of interesting results have been obtained. For example, that bacteria are much more contagious than was ever thought. If one latent bacterium is present in a lot of seed potatoes, contamination can start spreading, via the soil, for example. Research has shown that bacteria move about in the soil and that they can cause a spreading of the infection during the growing season via the roots of the potato plants. Moreover, it was discovered that the number of plants that is latently infected with Erwinia is much greater than the number with visible symptoms in the field. This is important information for the inspection service, and the project group wonders whether this must have consequences for the inspection of lots of seed in the future. Mother tubers a danger for contamination (photo 002) To harvest seed that includes mother tubers can be very dangerous, with regard to the spreading of Erwinia. This should not really be new for seed potato growers. Recent study by the project group has once more shown how dangerous these mother tubers can be. Mother tubers that are infected with Erwinia will continue to carry the infection, even if they are In view of the spreading of Erwinia, it can be quite dangerous to lift seed that contains mother tubers. During the growing season, infections from unclear sources can contaminate a clean crop via damaged stems and via damaged or undamaged roots. almost entirely rotted away. If these plant remains are lifted with the crop, they can become a source of puddling and easily contaminate healthy tubers. Infection or penetration in the tuber need not necessarily take place, because research has also shown that Erwinia bacteria in rotted tuber remains can survive on the skin of a tuber for at least a month, even after a drying process. So, if the tuber gets damaged at a later stage, or if it comes into contact with another damaged or rotting tuber, infection can still be passed on. Fewer mother tubers with pregermination (photo 003) It is therefore important to take precautionary measures to prevent mother tubers from ending up in the harvested product, is the opinion of the project group. For that reason, a number of possible measures are being examined. By slightly pregerminating the seed, you start the growing process before you plant the tubers. Because of that accelerated growth, any possible 18 Potato World 2010 • number 1 Pagina 17
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