Pathogens can be seen in real time in lettuce leaves for the first time

With a growing world population of over 8 billion people, producing enough food is a challenge. The Netherlands is the second largest food exporter in the world and grows all kinds of crops very efficiently. However, plant diseases such as downy mildew are a common problem that can seriously damage the farmer’s harvest. Delft scientists have developed a method for the first time to monitor plant disease in real time, without killing the plant. The knowledge gained helps to grow new sustainable crops with higher yields and less use of pesticides. The investigation is now underway Nature Communication.

Sustainable crops

Farmers who grow lettuce prefer lettuce that is resistant to all kinds of diseases. This also applies to downy mildew, a common plant disease that causes yellow or brown spots on the top of leaves. Scientists from Delft looked at powdery mildew diseases in lettuce, a plant species in which you usually only see such a disease in the final stages. “There are varieties of lettuce that are weakly resistant to downy mildew, but just like with the coronavirus, the disease continues to evolve into new variants that can still outlast the resistant plants. to catch This forces scientists and breeders to breed new sustainable crops in a race with growing diseases,” explained physicist Jos de Wit, who worked with the Utrecht biologists for his PhD research.

Real-time management

In order to grow crops such as lettuce that are more resistant to diseases, researchers from TU Delft and Utrecht University have developed a method that allows you to create an image of common plant diseases. For the first time, this is possible without killing the plant and much faster than with a conventional microscope. “Until now, researchers had to kill a plant for each step in the process, stain it and then look at it under the microscope,” says Jeroen Kalkman, associate professor of physics imaging. “Now we can use a new imaging technique to monitor in real time how disease develops in a living plant.”

Higher yield

Plant scientists often do not know how disease progresses in the plant and what makes a particular crop insensitive to a pathogen. The instrument provides insight into this, which helps to breed crops with a wider resistance against various diseases. “These crops require less pesticides, are more resistant to severe weather conditions and therefore produce higher yields. In this way, more people on earth – in the end – will be able to be fed,” says Kalkman.

Mapping plant diseases

“The method we used is called dynamic optical coherence tomography (dOCT),” says De Wit. “You emit light and measure the time it takes for the light to to reflect, a type of ultrasound scanning with light instead of sound. This way you can take about 50 to 100 pictures of an infected lettuce leaf within a second and a half. We can clearly identify plant diseases with dOCT because the pathogens move more than the plant cells. By giving colors to areas with more movement, we can create a strong difference between the pathogen and the plant. Without dOCT you can’t see the disease but at a much later stage.”

Useful tool

In addition to lettuce, the scientists have shown that their instrument also works for other crops, such as radish and pepper with parasitic roundworms. However, further research is needed to make the technology an easy-to-use tool for biologists with no technical knowledge. Kalkman: “I would like to continue this research to bridge the gap between technology and biology.”