The infamous pathogen Phytophthora infestans caused famine in Ireland and other parts of Western Europe in the 19th century and continues to pose a major threat to our food production worldwide.
For a long time it was a mystery how this microscopic organism and other Phytophthora’s mechanically make their way through the outer protective layer on the leaves of agricultural crops. Plant pathologists, cell biologists and physicists from Wageningen University & Research have now found the answer to this question in a unique collaboration. Their discovery offers starting points for making the control of Phytophthora more effective, more efficient and more sustainable in the long term. The research is published in Nature Microbiology.
Plants are continuously threatened by all kinds of pathogens. A number of these attackers, with the difficult name Phytophthora (literally: plant destroyer), annually cause enormous damage to all kinds of crops such as potatoes, tomatoes, aubergines, cocoa, peppers, soy, and palms, but also in forests and nature reserves. Phytophthora therefore not only poses a major threat to our food security, but is also an enormous economic cost item that causes approximately 6-7 billion euros in annual damage in potato cultivation alone.
Fighting Phytophthora is and remains difficult, partly because the pathogen and its target are involved in a continuous arms race. In order to become less dependent on chemical crop protection, much is being invested in developing resistant crops through plant breeding and more attention is being paid to new forms of mixed cultivation.
Utilizing insights mechanics
Now another possibility presents itself; preventing Phytophthora from gaining access to a plant at all. Plants are equipped with a protective layer that targets burglars such as Phytophthora to ward off. Yet this microscopic pathogen (less than one-tenth the thickness of a human hair) manages to break through this layer and initiate the disease process in plants. Despite decades of research, it was not yet known how they mechanically break through that layer.
To solve this problem, plant pathologists and cell biologists from WUR joined forces with physicists from WUR. They specialize in mechanics, a branch of physics that deals with the equilibrium and movement of objects under the influence of the forces acting on them. Building on their collective knowledge and the joint development of new research tools, the riddle could finally be solved.
Sharp knife
“We have discovered that Phytophthora can use clever tricks to sharpen its tubular infection structure and then cut through the surface of the plant like a sharp knife. With this strategy, Phytophthora can infect its host without brute force and with minimal energy consumption. This is the first time that this mechanism has been brought to light and a truly fundamental discovery,” says Joris Sprakel , professor of Physical Chemistry and Soft Matter.
More effective and durable protection
Professor of Phytopathology Francine Govers sees plenty of starting points for making the control of Phytophthora more effective, efficient and sustainable in the long run, without the usual suspects of chemistry and plant breeding being involved. “The laws of mechanics tell us that Phytophthora cannot penetrate the plant without first attaching itself strongly to the surface of the leaf.” To test this idea, as the first proof of feasibility, the researchers sprayed the leaves of potato plants with a non-toxic and cheap substance that removes the adhesive power of the leaves. This allowed the rate of infection to be reduced by about 65%. In an optimized test on artificial surfaces, the effect even approached 100%.
Quick tests
In addition to the fundamental breakthrough and new tools for looking at the control of these types of plant diseases from a new perspective, the research has also yielded new methodologies, a kind of rapid tests, with which the effect of pesticides can be investigated in a fast, accurate and cheap way. This too could make an important contribution in the ongoing fight against plant diseases.
Govers: “Thanks to the involvement of Joris Sprakel and his team, including PhD student Jochem Bronkhorst , we now know that there are a number of fundamental physical principles that could potentially give a new turn to the arms race between pathogens and plants. All in all, this research is a really good example of how collaborations beyond disciplinary boundaries can lead to new breakthroughs.”
