Professor sees opportunities in fight against potato blight

For nearly a hundred years, the Wageningen Laboratory of Phytopathology has been working on Phytophthora infestans, the cause of the dreaded late blight disease. In the past, the focus was primarily on the mode of action of fungicides and fungicide resistance. In recent decades, emphasis has increasingly shifted to molecular research on the pathogen itself. Which genes are involved? What proteins play a role in infection? And how can infection and invasion be disrupted?

Molecular Phytopathology

This approach took off around the time Francine Govers joined as an assistant professor in the early 1990s. She was perfectly suited for the role. "I combined plant pathology with molecular biology, particularly the interaction between plants and microbes at the molecular level. This field of research was just emerging—an exciting time with lots of new insights."

The right person, at the right time, in the right place. In 2008, she was appointed professor, and on 27 September of this year, she delivered her farewell lecture. "In all those thirty years, I was the only female staff member in the Laboratory of Phytopathology. At international conferences, I always met many female colleagues, while here in Plant Sciences there were only a few female (associate) professors until about ten years ago. Fortunately, I see this changing, but I don’t think we’re anywhere near full equality yet. The ‘because she’s a woman’-argument, unfortunately, still exists, so there’s still a lot to be done in terms of diversity and equality."

Arms Race

A significant part of her working life at Wageningen University & Research has revolved around Phytophthora. There is an ongoing arms race between science, industry, and farmers on one side, and Phytophthorainfestans on the other. And you can certainly not say at this point that potato late blight is losing the race. In fact, this year, the problems are particularly severe likely due to the rise of resistance against two classes of fungicides.

And this continues: breeders develop new varieties that are more resistant, and the pathogen manages to escape that resistance. The same goes for new crop protection agents: they work well for a while, and then Phytophthora adapts.

To break out of this constant cycle, Govers drew inspiration from medical science. "Just like with human pathogens, you must know the enemy inside out to find its weaknesses. I’ve always thought of Phytophthora as a kind of 'friend' whose secrets I wanted to uncover so we can expose its vulnerabilities."

Phytophthora is not a fungus

Phytophthora looks like a fungus, but it is not a fungus. It’s an oomycete with many unique characteristics and highly suitable for infecting plants. But at the same time, according to Govers, these characteristics also provide opportunities for innovative control methods.

“Phytophthora has receptors in its cell membrane that are similar to those in humans. These receptors act as antennas for signals outside the cell, such as hormones or volatiles, and ensure that the response inside the cell is activated. Thirty percent of human medicines target such receptors. This offers opportunities for tackling oomycetes. They have many of these receptors that are unique and not found in other organisms."

"If you can intervene in signal perception, for example by blocking these unique receptors, you’d have a highly specific control agent without harmful side effects for plants, humans, insects, or beneficial microbes—safe for nature and the environment," she says. However, so far, it has been challenging to get market parties interested in this approach due to the large investments required.

Another interesting feature of Phytophthora are its zoospores. They thrive in moist conditions and can swim rapidly. "They can keep going for hours. They can sense and smell substances, for example, those secreted by the potato plant. They also attract each other and collaborate when invading the plant. We can now film them with a high-speed camera at many frames per second, allowing us to better understand their behavior. This is something quite recent."

According to Govers, this opens up many new possibilities. "You could lure the zoospores away with certain substances or somehow impair their swimming ability."

Microscopic powerhouse

The moment of plant invasion is crucial. Although the pathogen is microscopically small, invasion involves enormous forces. Phytophthora can develop pressures of up to 28 bar. By comparison, the air pressure in a car tire is around 2.5 bar. "Without that pressure, the pathogen cannot invade. So, you need to understand how that pressure is built. For some fungi, this is already known, and the development of a compound that can prevent this pressure buildup is ongoing. With Phytophthora we’re not that far yet, but there are opportunities," Govers explains.

Once inside the plant, the oomycete secretes hundreds of proteins, collectively called effectors, which have specific effects on plant cells. They often disrupt basic processes that keep the plant cell in balance but also the production of defense compounds that the plant uses to protect itself. "A breakthrough was the discovery that these effectors all have a small, common segment: RXLR, consisting of just four amino acids and acting as a postcode. It ensures that the effector is taken up into the plant cell. This might offer clues for a broad resistance against late blight."

Varying Varieties

But even without such broad resistance, the increased knowledge already allows for a more refined approach. A resistance protein from the potato plant recognizes the matching RXLR effector from Phytophthora and only then becomes active. "You can go out into the field each year to see which Phytophthora isolates are present and which RXLR effectors they secrete. Then you can take measures accordingly—for example, by growing specific varieties with resistance genes whose proteins recognize the effectors present. That means growing one variety one year and another the next," she explains. "But it will require faster breeding to get new resistant varieties onto the market more quickly. Think of potatoes that can be sown instead of planted and the use of new genetic techniques."

Looking back, Govers is proud of the great strides in knowledge she and her team, in collaboration with international researchers, have made. "Now the challenge is to translate all the developed insights into practical solutions so that more sustainable potato cultivation can indeed become a reality."

Want to know more? Watch here the farewell speech of Francine Govers.