Potato Cyst Nematodes (PCN)

World-wide Distribution

Potato cyst nematodes (PCN) comprise of two very closely related species (Globodera rostochiensis, Globodera pallida) which co-evolved with the potato in South America, but have subsequently been introduced elsewhere with the production of potatoes.  Outbreaks of potato cyst nematodes have now occurred in most of the potato growing areas of the world.  Probably the only country in the world growing a large acreage of potatoes that has yet to report an outbreak of PCN is China.  Reports of PCN remain scarce from some countries with extensive potato acreages, most notably Australia, Canada, USA, India and, probably, some parts of the former USSR.  PCN continues to be a quarantine pest throughout the world. 

PCN biology - impact on potato production

Symptoms of PCN attack on potatoes reflect those of plants with an inefficient roots system i.e. poor growth, wilting during periods of water stress, early senescence and reduced tuber yield up to levels in excess of 80%.  Although most PCN development occurs within the root system, the cyst mature outside the roots and then fall into the soil at harvest, making them easily transported within soil attached to tubers, especially in natural crevices such as tuber eyes.  Only under exceptional circumstances, e.g. at very high densities, will cysts be found directly attached to potato tubers. 

PCN control

The main route by which PCN spreads is through the movement of infested material, primarily soil which may be transferred with tubers, plants, waste material or farm machinery.  The higher the population of PCN in a field, the greater the risk of spreading it to other land.  However, if potatoes are grown in soil infested with PCN, the risk of transmission with tubers from such a crop can also be reduced by minimising the quantity of soil associated with those tubers.  Therefore, the key principles of PCN control are targeted at seed potatoes: ensuring that the land on which the seed is grown has been tested and the sample has been found to be free from PCN prior to planting and that a low tolerance (1%) is set for soil associated with seed potatoes for marketing. 

In the EU, one major step forward in PCN control from the old 1969 PCN Directive to the new 2007 Directive (2007/33/EC ) relates to the definition of seed potatoes.  For the purposes of the 1969 Directive, the legislative controls on PCN related only to seed potatoes that were marketed.  The 2007 Directive defines seed potatoes as any potatoes that will be planted, recognizing that the risk of spreading PCN relates to the movement of any planting material.