Potatoes with built-in immunity could end toxic fungicide spraying

But as the chemicals disappear, a bigger question looms: what will take their place?

Potatoes are the world’s third-most consumed food crop – after rice and wheat – and a cornerstone of food security across the world. But they are also the most heavily sprayed. In the fight against PFAS-contaminated water, no other crop represents the pesticide dilemma more clearly.

“Nowhere is the challenge more urgent than in potatoes. Late blight – the same disease that caused the Irish potato famine – still forces farmers in Europe to spray their fields up to 15 times each season,” explains Erik Andreasson, Professor of Plant Protection Biology at the Swedish University of Agricultural Sciences, Lomma, Sweden.

No other crop is treated more intensely in northern Europe.

From blight threat to genetic defence

Ask any potato farmer what keeps them up at night, and the answer is nearly always the same: late blight. Caused by Phytophthora infestans – the same rapidly spreading pathogen behind the Irish potato famine – it still gets farmers to spray fungicides as many as 10 to 15 times per season. Sometimes twice a week.

And despite all that effort, late blight can still break through.

This drove a research team in Sweden to try a different approach. More than a decade ago, they began engineering potatoes to fight late blight themselves – by borrowing immune genes from wild potato relatives and inserting them into familiar varieties such as King Edward.

“We do not rely on spraying anymore. The plant’s own immune system takes over,” Andreasson adds.

With PFAS concerns rising and pesticide bans gaining momentum, the timing of their results could not be more relevant. But understanding why potatoes are now at the centre of the fight for sustainable farming requires examining the genetics.

Why traditional breeding does not work

Breeding better potatoes is notoriously difficult. Unlike barley, potatoes carry four sets of chromosomes organised in a special way – making their genetics unpredictable and messy.

“You need 50 traits – taste, texture and yield – and crossing them usually ruins something,” says Andreasson.

Combining resistance genes through traditional methods rarely works. In tetraploid potatoes, gains in one trait often come with losses elsewhere. Further, potatoes are easy to regenerate from single cells.

“That led us to try genetic tools – to do what traditional breeding cannot.”

From wild weeds to immune potatoes

Even when breeders manage to introduce resistance, it rarely lasts. The pathogen evolves – and late blight comes roaring back.

That shift led Andreasson’s team to wild potato relatives – especially Solanum americanum, a tough little plant.

“It is close to a Nordic weed most people ignore,” Andreasson says. “But it carries immunity we just cannot get through conventional breeding.”

To test its potential, two of its immune genes – Rpi-amr1 and Rpi-amr3 – were transferred into a major commercial potato cultivar. The researchers also transformed King Edward, a major classic Swedish variety still used on dinner tables today, with a combination of three immune receptors (resistance genes).

“We used Agrobacterium – nature’s own standard method,” Andreasson explains. “And the King Edward potato is still what most Swedes eat.”

Potatoes, it turns out, are unusually cooperative. They respond well to genetic transformation and can easily regenerate from just a few cells.

“Biotech works,” he says. “In potatoes, it is actually easier than in many other crops.”

Field trials put resistance to the test

The real test came outdoors. The researchers planted the modified King Edward and other potatoes side by side with conventional lines and resistant varieties such as Bionica and Sarpo Mira – without spraying a drop of fungicide.

“We wanted to see what happens under real disease pressure,” says Andreasson.

When late blight swept across the fields in southern Sweden, the difference was immediate.

“The regular plants got hammered. The ones with the resistance genes stayed green.”

Using a simple scale from 1 to 9 to rate disease symptoms, the stacked lines consistently scored 8 and 9 – even when blight pressure peaked.

“We saw just a few tiny lesions,” he recalls. “They held up incredibly well, all lines.” Nevertheless, these were small trials, so larger areas of cultivation at several places and with different pathogen populations are recommended for the future.

Crucially, the best results came when several genes were used together.

“The combination of Rpi-amr1 and Rpi-amr3 gave the strongest protection. That pairing worked better than either on its own.”

Building immunity that lasts

Encouraged by these results, the team is now testing a four-gene stack – including new, barely explored resistance genes – to stay ahead of evolving pathogens.

“We drew up a plan years ago to rotate immune genes every five years,” Andreasson says. “Now we are finally testing that strategy in the field.”

Tools such as CRISPR are accelerating the work. They let researchers fine-tune mutations and remove unwanted laboratory elements from earlier methods. Also, the position of an insertion can be determined.

“CRISPR lets us clean up the process – no antibiotic resistance markers, no leftover DNA,” Andreasson explains. “It is faster, more precise and it works.”

It will also work better together with legislation, and in the Nordic countries, the potato is a model system for this development. The goal is to build flexible gene batteries – resistance combinations that can lie dormant and activate only when pathogens attack.

“With the new biotech tools, we can have a chance to keep up with the evolution of the pathogen, and even in the future make the potato a non-host to late blight: no late blight symptoms at all, such as wheat.”

This vision is based on the fact that most plants are fully resistant to most pathogens.

“These genes do not misfire,” he says. “They just sit there and wait. When the pathogen appears – bam!”

Better than today’s resistant varieties

To see how their modified potatoes stacked up, the researchers compared them with Bionica and Sarpo Mira – two varieties known for their natural blight resistance but no longer major cultivars because of other suboptimal traits.

The new lines performed just as well – or even better – especially under real, uncontrolled field conditions.

“We also tested Bionica and Sarpo Mira,” says Erik Andreasson. “But the new ones actually did better in some years – especially when the blight pressure was high.”

For the team, this was more than a good result. It was proof of concept – not just for these two genes but for the bigger idea: that stacking multiple resistance genes can build more durable and reliable plant immunity – even in a complex pathogen population.

“Crucially, the protection has lasted. These Solanum americanum genes have now been through multiple years of field trials – and they are still holding up. This is not just an experiment anymore,” Andreasson says. “It is a proven strategy. These genes have even been bred and sold commercially.”

“The blight comes every year. You cannot afford to lose a season – that is why we need something that lasts.”

Stacking genes makes resistance more durable

After years of research, the results are clear: stacking resistance genes from Solanum americanum offers a reliable path to long-lasting protection against late blight in potatoes.

Unlike older resistance genes – which often failed after a season or two – these new ones have held up through multiple years of real-world field trials.

“The old genes were too specific,” says Erik Andreasson. “They worked for a while, and then the pathogen adapted. But these new ones – especially from Solanum americanum – seem broader. We do not fully understand why, but they are clearly better.”

The key insight is simple: when you stack genes, you create layers of defence. If one fails, the others step in.

“We are stacking genes because one on its own will not manage,” Andreasson explains. “If the pathogen breaks through one, the others can still hold the line.”

And this is not theory. The durability is backed by years of trials under real field conditions – with no spraying and full infection pressure from potato-growing areas.

“This is not just a greenhouse result,” he says. “It is based on real disease pressure in real fields. That gives us confidence.”

Rules still block disease-resistant crops

The science and potatoes are ready – but the policy is not. Despite years of safe use and clear benefits, genetically modified potatoes are still banned in most of Europe.

“Legislation is now the main obstacle,” says Erik Andreasson. “It is not the science – it is the rules.”

The irony stings: spraying crops 15 times is legal – but inserting a resistance gene from a wild crop relative is not.

“You can spray a field 15 times,” says Andreasson. “But add one gene, among 20,000 others, that lies in wait – and that is the bigger risk?”

And while some claim that traditional breeding could achieve the same thing, researchers say that this is not realistic – at least not for potatoes.

“It is a myth,” Andreasson explains. “You might do it in wheat or barley. But in potatoes, it is too complex. Currently, you cannot just cross your way to this kind of resistance and keep the other desirable traits.”

In fact, the idea of rotating resistance genes – switching them out every few years to stay ahead of the pathogen – has been around.

“But the science moved forward, and the legislation stayed behind.”

Editing genes to bypass old rules

There are signs of progress. Denmark is discussing special gene rotation zones, and researchers are developing a new method: editing the potato’s own DNA to add resistance – without introducing genes from other species.

“We are working on ways to edit these genes directly into the potatoes people already grow,” says Erik Andreasson. “No foreign DNA. That could finally make this usable in Europe, and right now Denmark is serving as the Presidency of the European Union.”

For the team, the trials focus on more than data. They are a way to keep the conversation and knowledge alive.

“One reason we keep doing this in Sweden is to make sure it does not disappear,” Andreasson says. “If we stop the trials, the whole thing goes invisible in the European Union. And that is worse.”

Pesticide bans require real alternatives

The researchers are watching Europe’s pesticide debate with growing urgency.

“Everyone is talking about banning fungicides – and that is a good thing if they are dangerous,” says Erik Andreasson. “But we also need to make room for the alternatives. Otherwise, farmers are stuck.”

Many researchers say that maintaining food security without alternatives to pesticides will be difficult if not impossible.

And these alternatives are not new. Durable genetic solutions have been technically feasible for years.

“In 2009, I sketched out a plan to rotate resistance genes every five years,” Andreasson says. “But the policy never caught up. So we are still stuck with varieties with no long-term resistance.”

The irony is hard to ignore: the European Union wants to phase out toxic spraying and yet blocks the nature-based solutions and tools that could replace it.

“If we are serious about phasing out fungicides – and we should be – then we also have to enable the solutions,” he says. “Otherwise, we might need to import the produce from countries that do not have these rules.”

Smarter potatoes, safer future

With pesticide bans accelerating – and the health risks of PFAS-contaminated water making headlines across Europe – the need for safe, lasting alternatives has never been clearer.

The researchers behind the Swedish potato trials are not claiming that biotech is a silver bullet. But they do think that it is one of the most powerful tools we have – especially for crops such as potatoes, in which traditional breeding falls short.

“We are not saying that biotech is the only answer,” says Andreasson. “But if we do not use it where it works, we are missing the point, and as the Danish Council on Ethics has pointed out, failing to use these new biotechnical tools is unethical.”

Genetically edited, disease-resistant potatoes will not eliminate the need for good farming practices. But they could dramatically reduce dependence on chemical spraying – and help to secure food production in a changing climate.

And while the European Union debates the rules, the blight is not waiting. “The disease keeps coming,” Andreasson says. “Year after year. What we have built is not just a trial – it is a strategy. And it works.”

As countries phase out chemical spraying, these smarter potatoes might not just be a scientific milestone – they could be a sign of what sustainable farming looks like in the years to come.