"Detected early, danger averted" - this successful concept in plant protection could be used in the future with sophisticated technology: Researchers have developed a patch for leaves equipped with sensors that can show the subtle signs of infections with pathogens or stress in plants at an early stage. In tests, the patch prototype was able to detect a virus infection in tomatoes based on the pattern of data collected - more than a week before visible symptoms of the disease appear, the scientists report.
When leaves are curling and shoots are hanging, it is often too late: the diseased or damaged plants can then often no longer be saved and the pathogen has often spread unnoticed in the stock. This is annoying for hobby gardeners - for farmers, however, certain fungi and viruses or yield losses due to unfavorable growth conditions can threaten their existence. Early action is therefore key: "The earlier farmers recognize infections, the better they are able to contain the spread of the disease and protect their crops," says senior author Qingshan Wei from North Carolina State University in Raleigh. Likewise: "The faster farmers can identify abiotic stress factors, such as salt-contaminated irrigation water, the better they are able to cope with the corresponding challenges and improve crop yields," says the researcher.
Early diagnoses are required
However, the techniques for diagnosing plant problems are not exactly fixed so far: After sending in a sample, it can often take a long time before the test result is available. However, it may be too late by then. Wei and his team have therefore been developing technologies for the early detection of problematic plant conditions for several years. Their concept is mainly based on "sniffing out" signs: They explain that plants emit certain patterns of volatile organic compounds (VOCs) when they are infested with pathogens or are otherwise under stress. In order to develop a technical "nose" for these substances, the researchers coated sensors with various chemical ligands that react to the presence of certain VOCs.
"The new patches contain additional sensors that allow them to monitor temperature, ambient humidity, and the amount of moisture 'exhaled' by plants through their leaves," says co-author Yong Zhu of North Carolina State University. The patches are only 30 millimeters long and are made of a flexible material that contains the sensors and electrodes made of silver nanowires. So far, they have been connected to a data acquisition device via a cable. The patches are attached to the underside of the leaves because they have a higher density of stomata. These are the pores through which plants “breathe”: They exchange gases with the surrounding air and also release VOCs from the plant.
Promising test results
The researchers tested the new patches on tomato plants in greenhouses and experimented with patches containing different combinations of sensors. The tomato plants were infected with various pathogens, including the tomato bronze spot virus, which can cause significant damage to crops. The plants were also exposed to a range of abiotic stresses, such as overwatering, drought, lack of light and high salt concentrations in the water. The scientists then processed the data that the patches provided in these experiments using a form of artificial intelligence: machine learning helped determine which combinations of sensors are most effective for detecting the respective plant problems.
As the team reports, the potential of the concept for automatic early detection of abiotic and, above all, biotic threats was clearly evident: "Our results for detecting the challenges tested were consistently promising," says Wei. “For example, we found that with a combination of three sensors, we were able to detect tomato bronze spot virus four days after the plants were first infected. This is a significant advantage, as tomatoes usually only show noticeable symptoms of the disease after 10 to 14 days,” explains the scientist.
The researchers say they are now just two steps away from a practical system. First of all, they want to make the patch wireless - it should be able to supply itself with electricity and transmit its data wirelessly. Second, they need to test the patches outside of greenhouses in the field to ensure they work in real-world conditions. "We are currently looking for partners from industry and agriculture to help us develop and test this technology," says Zhu. He and his colleagues are convinced of the potential: "This could be a significant advance, helping farmers to prevent small problems from becoming big ones, and thus helping us all to tackle food security challenges in a meaningful way." , according to the scientist.
Source: North Carolina State University, professional article: Science Advances, doi: 10.1126/sciadv.ade2232