Plant-parasitic nematodes on the rise:

TO get a clear picture of the proliferation of novel nematode species and populations and to find appropriate and sustainable solutions to these problems, Wageningen University & Research (WUR) in the Netherlands is launching a major research and innovation project with 17 European partners called NEM-EMERGE. 

Climate change and genetic selection have brought root-knot nematodes further north in Europe and made cyst nematodes more difficult to control. These emerging parasites pose a huge threat to potato crops. 

The WUR project has been accepted as a Horizon Europe Project, resulting in 7 million euros in funding. 

Researcher Hans Helder said: "They drain energy from the plant, causing a plant condition referred to as  'fatigue'. As a result, the crop barely grows and is severely weakened, leading to crop loss and hence economic damage. 

"Annually, root-knot nematodes alone cause yield losses of several billion euros. Next to crop rotation and resistant varieties, growers currently use broad-spectrum chemicals to control these nematodes which have unwanted negative side-effects on  nature and the environment."

Both root-knot nematodes and cyst nematodes are on the rise. According to Helder, climate change is a major cause of this. "Our winters are becoming milder. As a result, ‘tropical’ root-knot nematodes are moving further north. Whereas they used to be found only in North Africa and southern Europe, in recent years they have also been observed in central France and halfway across the Balkans. 

"In addition, climate change is affecting soil temperatures. At temperatures of 28 degrees or higher, some important resistance genes of crops no longer work. This line of defence that protects plants against parasites is thereby lost. Besides climate change, genetic selection is another driver that plays a role in the emergence of nematodes. Frequent use of a limited number of resistant crop varieties resulted in the rise of nematodes that are less sensitive to these resistance genes." 
Mapping the scope of the problem
Hans said the team is going to investigate the current distribution  of root-knot nematodes to find exactly where are they currently occur. 
"From southern Turkey and Spain to northern Germany, we are going to take soil samples about every two to three hundred kilometres to investigate the presence of plant-parasitic nematodes. Based on the resulting picture, modellers can predict where we can expect them in five or 15 years.’ 

His colleague Aska Goverse aims to tackle the instability of resistance genes in plants under higher temperatures in one of the other work packages. 

"We have been working on the molecular mechanisms that underly the (mis)functioning of resistance genes for several years," said Aska. "We have a pretty good view of the factors determining their function for some diseases, but not yet for these plant-parasitic nematodes. 

The researchers will work on solutions in close cooperation with end-users. As the use of pesticides is increasingly restricted within the EU, farmers seek alternative methods. 

Aska said: "Growers require knowledge and practical tools to make a transition towards sustainable agriculture. The EU is steering towards integrated crop management, but what tools are needed to reach that goal? How can we, for instance, boost the soil’s disease-suppressive potential? At the same time, researchers want to know the demands and the conditions for innovation from an end-user’s perspective. The ultimate goal is to develop solutions that can be put into practice."

There is no single silver bullet solution, Hans warned. "We cannot afford to focus exclusively on, for example, new resistant varieties because it is only a matter of time before a new population of nematodes emerges that can break this resistance. We must really focus on a wide range of measures, from plant resistances to more hygienic working practices to the stimulation of natural enemies." 

He emphasised the importance of collaboration between research groups. "It is already there, but only sparingly. The breadth of the consortium, from growers to universities, gives this project an extra dimension. We hope that this project can be the oil that will greatly boost cooperation between European research centres." 

NEM-EMERGE is a collaboration between 18 European partners. These include knowledge institutions from Spain, France, Scotland, Turkey and Slovenia, among others, as well as organisations and companies specialising in biological control, plant health and breeding. Besides the official project partners, NEM-EMERGE also involves local stakeholders.

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