Plant-parasitic nematodes: new waste management solutions
Nematodes are parasitic worms, some species of which cause major crop losses. To prevent their spread, it is important to disinfect organic waste – plants, soil and sludge – and water that have been in contact with these pests before discarding or reusing them. Scientists from ANSES's Plant Health Laboratory have assessed the effectiveness of various disinfection methods enabling this waste to be recovered and reused as part of the circular economy.
The potato cyst nematodes Globodera pallida and Globodera rostochiensis are responsible for the loss of around 9% of the world's potato crops. These pests, for which control measures are mandatory, are very difficult to eradicate: the eggs, protected in cysts, can survive for several years in soil. If a plot of land becomes contaminated, it will be necessary to wait until the larvae are no longer viable before potatoes can be planted again.
Plant waste, soil, sludge and water can spread these worms after being in contact with them. These materials should therefore be thoroughly disinfected before they are discarded. This obligation mainly concerns the food processing industry, which must dispose of produce deemed unfit for consumption, soil waste, and washing water; it also applies to laboratories that study or are in charge of detecting these nematodes.
A reduced environmental impact
As part of a research project, scientists from the Nematology Unit of ANSES’s Plant Health Laboratory, in collaboration with the French Federation of Seed Potato Producers (FN3PT), conducted experiments to test the effectiveness of various methods of disinfecting washing water and other waste contaminated by these organisms. The aim was to find alternatives to the processes usually used, as some of these are not entirely effective or can negatively affect the environment. The results of their work were published in the scientific Journal of Environmental Management this past December.
Their experiments showed, for example, that heat treatment can be carried out below the 80°C usually used for these organisms, provided that it is applied for longer periods of time. Treatment at 60°C for three minutes or at 50°C for half an hour can kill the nematodes while requiring less energy. The effectiveness of this method was successfully tested not only on the genus Globodera, but also on two other species of plant-parasitic nematodes, i.e. the root-knot nematodes Meloidogyne chitwoodi and Meloidogyne fallax.
Effectively treating waste while reusing it via the circular economy
ANSES's scientists also experimented with organic matter recovery processes, such as composting, anaerobic digestion and reed-bed systems, that can be used in the circular economy. Previously, their effectiveness in eliminating cyst nematodes had not been properly evaluated. “Composting and anaerobic digestion were very effective at killing these nematodes under all the conditions we tested” affirm the study’s authors. “This result is very interesting because food manufacturers can be required to reject an entire crop when a nematode infection is detected in a commercial batch. These alternatives would enable this infected produce to be recovered for reuse”.
On the other hand, reed-bed water treatment produces highly variable results. Nematode control appears to be highly dependent on climatic factors, making this an unreliable method for eradicating these pests under the conditions tested.
The study's authors point out that before adopting any of the tested treatment methods, interested laboratories or manufacturers should ensure that nematodes and other infectious agents have been effectively eliminated from their work sites: “These methods worked in our laboratory and on our experimental sites. However, we cannot guarantee that they are effective regardless of the conditions” they explain. “Furthermore, we studied their effects on specific nematode species and our results cannot be extrapolated to all plant pathogens”. This was nevertheless a first demonstration of the effectiveness of these alternative disinfection processes targeting pests known to be highly resistant.
Regulated nematodes
Globodera pallida, Globodera rostochiensis, Meloidogyne chitwoodi and Meloidogyne fallax are quarantine pests: efforts to control their spread are mandatory and they are covered by a national surveillance plan. Moreover, anyone wishing to import or export a plant must prove that it is free of these nematodes. The Nematology Unit of ANSES's Plant Health Laboratory is the reference laboratory for France and the European Union for plant-parasitic nematodes. As such, it guarantees the reliability of the analyses carried out to detect them.