Potato cyst nematodes (potato fatigue)

Potato cyst nematodes, the roundworms responsible for potato fatigue, are divided into two species: Globodera rostochiensis (Ro) and Globodera pallida (Pa). Both species consist of different groups, called pathotypes. These pathotypes differ in their ability to reproduce on resistant varieties of potato.

For G. rostochiensis, there are five different pathotypes: Ro1, Ro2, Ro3, Ro4, Ro5, of which Ro1 is the most common type and Ro4 and Ro5 the least. Within G. pallida, there is much variation between populations; however, there are not any clearly distinguishable pathotypes.

Most starch varieties possess resistance to both types, but some varieties are only resistant to one of the two species or, in the case of G. rostochiensis, not resistant against all pathotypes.

More and more consumer varieties that are resistant to both species are becoming available. When it comes to infection with G. pallida, the impact of a resistant variety depends on the population, i.e. the extent to which a resistant variety reduces the population can vary from field to field.

Note that mixed infections of different pathotypes can also occur. It is important to monitor the effect of the resistant variety by sampling.

Species determination

If an infestation is found, it is very importance to have a species identification carried out to determine whether the infestation is caused by G. rostochiensis, G. pallida, or both. This is an important first step for proper variety selection. Currently, such species determination can be performed using PCR techniques. With this technique, the species is determined on the basis of DNA. The test is very reliable, partly because a much larger number of cysts can be reliably tested in one determination.

Variety selection

To prevent damage in starch and ware potato cultivation, it is not necessarily crucial to choose varieties that reduce the nematode population by 80%, as varieties that give a greater or lesser degree of multiplication are also useful for controlling AM. The level of resistance needed to complete a cropping plan depends on the cultivation frequency and the aggressiveness of the nematode population present; the lower the frequency of cultivation, the higher the level of resistance. It is estimated that within a 1 in 4 rotation, a relative susceptibility (RH) of 25% or lower is sufficient to prevent damage without soil fumigation. For a 1 in 3 rotation, this is an RH of 15%, and for a 1 in 2 rotation an RH of 10%. At 1 in 5, it is 37%.

Symptoms in the field (potato):

• General slowed growth or regularly formed drop spot
• Drop spot, usually oval in shape
• Small plants in the middle of the spot, larger plants towards the outside
• Crop closes later or not at all
• Different flowering stages

Recognition on the root (potato):

• From mid-June, white globules start to become visible on the roots of susceptible varieties
• The species can be recognized by the discoloration of the cyst
• Cysts of Globodera pallida discolor from white to brown
• Globodera rostochiensis cysts change color from white to yellow to brown
• Note: With resistant varieties, very few cysts can be found on the roots. This does not mean that damage has not occurred.

Source: Actieplan Aaltjesbeheersing. Het Actieplan is een initiatief van het voormalige Productschap Akkerbouw en LTO Nederland.