Most countries require imported potatoes, if not all plant material and soil, to be free from Potato Cyst Nematodes (PCN). For seed exports, a phytosanitary certificate issued on the basis of a pre-crop soil test is a generally accepted means of assuring PCN freedom. As PCN cannot be detected by the visual inspection of harvested tubers, standard pre-export inspection for health and quality cannot confirm the presence or absence of cysts. Cyst detection at this stage necessitates laboratory examination. Information on countries requiring pre-export consignment tests for PCN is available on the Potato Export Conditions part of the Scottish Government website.
The soil for a consignment test is collected from a representative sample of bags of tubers, by staff from the Scottish Government Agriculture and Rural Delivery Division Area Offices. The number of bags chosen is on a sliding scale, from a minimum of 5 bags at 5 tonnes, to 10 at 20 tonnes, with a further bag for each additional 10 tonnes. It is important to keep soil contamination to a minimum, although it can be difficult to reduce the amount of soil to the 'dusting' demanded by some countries. The Scottish Government operates to a maximum soil tolerance of 0.5% by weight.
At SASA, the sample is prepared for examination by using a two sieve method. Larger samples may be processed using a fluidising column, or Trudgill Tower. Detection of any cysts present is achieved by visual examination of the extracts from the sieves.
If PCN cysts are found, the lot concerned cannot be exported or treated as seed. However, further lots from the same crop can be considered for sale, providing they are cleared by further soil testing.
If necessary, consignments from ware crops can be given phytosanitary clearance by a post-harvest field test, taken exactly as the pre-crop soil test, or by a consignment test on soil riddled from harvested tubers.
Results from consignment tests are issued via the agricultural officer from the the local Area Offices who collected the sample.
If you have any technical enquiries about consignment testing for PCN, please contact Jon Pickup.