Causal agent(s) and transmission
Several types of wet rot can be found on potato tubers. They are caused by various Oomycetes, belonging to the family Pythiaceae, such as Phytophthora erythroseptica, responsible for pink rot disease.
This pathogen can survive in the soil for several years as thick-walled oospores and has a wide host range on which it is often the cause of the damping-off of seedlings.
On potato plants, it penetrates the tubers through the wounds and via stolons, eyes and open lenticels.
Though pink rot can be very damaging to potato crops, his occurrence in continental Europe is fairly uncommon. Nevertheless, due to elevated optimal growth temperatures (above 20°C), there is a small risk of the disease occurring in southern European countries.
Symptoms on tubers
Tuber rot often begins at the heel-end, with brown spots on the surface (photo 1); in the flesh, the affected areas are separated from the healthy ones by a blackish border.
The flesh tissues become elastic but remain dense, unlike rot symptoms due to bacterial contamination. When the tuber is cut, the flesh turns red on exposure to air, then black within one hour (photo 2).
The development of this pathogen is favoured by high soil humidity and moderate to elevated temperatures.
P. erythroseptica grows during warm period but has a lower optimal temperature compared to Pythium spp.
Monoculture or intensive potato production, added to favourable environmental conditions and the presence of primary sources, may increase the severity of the disease.
- Use healthy seed potato tubers (cultivar resistance is not yet available).
- Maintain a lengthy crop rotation and make sure fields are properly drained to avoid water excess in soils.
- Keep harvest damage to a minimum.
- Ensure good skin set prior to harvest and avoid harvesting during hot and humid periods. Dry the tubers quickly and thoroughly after harvesting and prior to storage.
- Ensure good ventilation during storage to prevent condensation.