6. SURVEILLANCE AND TESTING
6.1 Surveillance
6.1.1 The Ring Rot Directive requires all Member States to survey their potato production for Cms. Operations carries out this survey each year, taking samples from crops grown from non-Scottish seed, one sample from each grower in Scotland and a representative sample of additional Scottish crops. In addition, non-Scottish seed potatoes introduced into Scotland for planting may be tested for both ring rot and brown rot, based on an assessment of the risk they pose.
6.2 Sampling and testing for ring rot
6.2.1 Testing for ring rot must follow a specified test methodology as laid down in Annex I of the Ring Rot Directive. Positive confirmation of the result will take between a few days and several weeks.
6.2.2 Samples collected for testing will normally consist of 210 whole tubers, of whatever size. Official sampling will be undertaken by Operations staff, although in some cases it may be agreed that non-official samples will also be submitted for testing, to provide additional coverage.
6.2.3 Routine testing will be of 200 tubers, as required by the Directive, and the remaining 10 will be 'spares' in case of loss etc. in transit. This gives an 87% chance of detecting a 1% level of infection, assuming that the sample is representative of the total lot. Much larger samples however need to be tested to detect low levels of infection in stocks and to give a high level of assurance that ring rot is not present in a stock. Recent work in Belgium has shown that up to 20 samples of 200 tubers had to be taken and tested to detect a very low level of infection in a large stock. In an outbreak situation there may be occasions when it will be necessary to undertake more intensive sampling and testing of individual stocks, for example to screen potentially infected seed stocks or to investigate the primary source of an outbreak. Such decisions will be decided on a case by case basis by the Incident Management Team (see section 7.4).
6.2.4 The Directive requires a 3-stage testing procedure comprising an initial screening test and, if initial results are positive, further diagnostic and pathogenicity tests. The initial screening test employed is immunofluorescence (IF). In cases where positives or suspicious results are found with IF further tests including real-time and conventional polymerase chain reaction (PCR) tests are performed. If a negative result is obtained from these tests, the sample can be considered free of infection. If the IF and PCR tests are positive, an eggplant bioassay test must be carried out to confirm presence of the bacterium. The initial diagnostics tests, including IF and PCR, can take 5 days to perform, whilst final confirmation by bioassay will only be available after several weeks.