A new study reports the synthesis of a targeted peptide that attacks Phytophthora infestans (P. infestans) – the pathogen responsible for late blight – in potatoes and tomatoes, without harming other plants. The research was led by scientists at KTH Royal Institute of Technology in Stockholm, in collaboration with partners in Italy, India and Australia.
Nearly 200 years after P. infestans triggered the catastrophe known as the Irish Potato Famine, the pathogen remains one of the world’s most destructive crop diseases. During the 19th century crisis, Ireland lost around a quarter of its population to starvation and emigration.
Today, late blight continues to cost farmers billions of dollars annually and threatens staple crops worldwide. While modern disease management has prevented famine on a comparable scale, researchers warn that climate change is increasing the risk of outbreaks by creating warmer, wetter conditions that favour rapid disease spread.
“Regions that once saw late blight only sporadically – from cool highlands to temperate fringes – are now experiencing longer and more intense infection windows as seasons become warmer and wetter,” said Vaibhav Srivastava, a glycoscience researcher at KTH.
“At the same time, more aggressive and diverse P. infestans populations are exploiting these new niches, challenging spray calendars and resistance strategies that were designed for yesterday’s climate,” he added.
Targeting a long‑overlooked vulnerability
The researchers’ approach exploits the unusual biology of P. infestans. Although often referred to as a “water mould”, the pathogen belongs to a group called oomycetes, which are more closely related to algae such as kelp than to fungi.
Unlike fungi, oomycete cell walls are largely composed of cellulose and other complex sugars, with little or no chitin – leading many scientists to question whether targeting chitin production would be effective.
The study challenges that assumption by showing that an enzyme known as PiChs does in fact produce specific chitin fragments essential to the pathogen’s growth and ability to infect plants. Blocking this enzyme, researchers found, significantly weakens the pathogen.
The newly developed peptide, known as CS5, was designed to bind precisely to this enzyme.
“CS5 is engineered to match and bind to this singular enzyme,” Srivastava said.
Promising lab results
In laboratory tests, CS5 successfully blocked PiChs activity, slowing or stopping the growth of P. infestans. Treated potato samples showed no signs of infection, while untreated samples developed characteristic late blight symptoms within days.
Importantly, the researchers say the peptide is highly specific, targeting an enzyme that does not exist in humans or plants.
“We’ve shown that this pathogen depends on a specific internal process to grow – and that a specially designed peptide can switch it off,” Srivastava said. “This gives us a completely new way to fight late blight.”
He added that the approach could work alongside existing disease‑management strategies and help reduce reliance on chemical fungicides.
“It has the potential to slow the development of resistance while allowing farmers to depend less on broad‑spectrum sprays,” he said.
Towards greener crop protection
The researchers say CS5 and related compounds could form the basis of a new generation of environmentally friendly crop‑protection tools, either used alone or in combination with other targeted treatments.
Such approaches could help farmers protect yields while cutting the environmental impact associated with conventional fungicides. The findings may also open the door to peptide‑based controls for other economically damaging oomycete pathogens.
The work was carried out through an international collaboration involving the University of Milan, Flinders University, and the Indraprastha Institute of Information Technology.
