Causative agent and transmission
Several species of root-knot nematode of the genus Meloïdogyne can cause damage to potatoes (reduced yield, external deformation, internal necroses).
Some species of Meloïdogyne are very common in hot climates, from the Mediterranean basin to the tropics: M. arenaria, M. javanica and M. incognita.
Other species are more adapted to Mediterranean and temperate conditions : M. hapla, M. chitwoodi, M. fallax.
Nematodes are transmitted by potato tubers, with or without symptoms, and by all root plants (tomato, lettuce, etc.). They are extremely polyphagous and develop on many crops (beetroot, carrot, cereals, rye, rapeseed, etc.) and weeds (nightshades, etc.). Furthermore, M. chitwoodi and M. fallax develop on graminaceous plants. Therefore, they are very difficult to eradicate.
Description of symptoms
(clic on photos to enlarge)
• On plants: dwarfism.
• On roots: warts.
• On tubers: warts or smooth swellings on the tubers, sometimes resembling common scab blisters.
Inside the tubers, small gelatinous or translucid whitish masses can be seen under the skin which correspond to the nematode females and their adhering masses of eggs.
The symptoms can evolve afterwards into internal reddish blemishes.
The species can only be identified in the laboratory.
M. chitwoodi and M. fallax are classified as quarantine parasites.
Control is difficult due to the very extensive range of associated hosts:
- Choosing healthy seed potatoes and controlling those brought in from affected areas;
- Early planting, because the disease develops particularly well under hot conditions (late autumn);
- Nematicidal treatment in the event of substantial infestation;
- A total cleanout with fallow rotation for one to two years, or using a cereal crop in the case of M. arenaria, M. javanica or M. incognita;
- No variety of potato is resistant to them. But other plants are resistant to M. arenaria, M. javanica and M. incognita (tomatoes with the M genus) and can be used successfully in crop rotation.