Researchers at North Carolina State University have developed an electronic patch that can be applied to the underside of a leaf to monitor it for the first signs of viral or fungal infections or for other stresses, such as salinity or drought.
Test results showed the patch could detect a viral infection more than a week before growers could see the first signs of a disease.
“This is important because the earlier growers can identify plant diseases or fungal infections, the better able they will be to limit the spread of the disease and preserve their crop,” said Qingshan Wei, assistant professor in chemical and biomolecular engineering.
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“In addition, the more quickly growers can identify abiotic stresses, such as irrigation water contaminated by saltwater intrusion, the better able they will be to address relevant challenges and improve crop yield.”
The technology detects disease by monitoring volatile organic compounds, or VOCs, emitted by plants. Plants release different combinations of these compounds depending on different circumstances. The sensors can alert growers to problems by responding to specific compounds in the moisture exhaled by the leaves.
The patches are about the size of a postage stamp. They consist of a flexible material containing the sensors and silver nanowire-based electrodes. Future research will be to make the patches as small and light as possible.
“Size and weight were two priorities and were the initial critical requirements when formatting the patch to be put on the leaf,” said Wei. “We don’t want to bend the leaf or create additional stress. We have to make all the materials as tight as possible. The electrodes are made from nano materials, extremely small and low density.”
Wei’s team tested the patches on greenhouse tomato plants. The patches were secured using double-sided tape on the underside of tomato leaves where there is a higher density of stomata, the pores that let the plant breathe and exchange gases with the environment.
The test plants were infected with three pathogens — tomato spotted wilt virus (TSWV), early blight (a fungal infection), and late blight (an oomycete). They were also exposed to overwatering, drought, lack of light and high saltwater concentrations. The researchers then experimented with different combinations of sensors.
“In the current patch, we only included four different VOC channels,” said Wei. “In each channel there are different chemical ligands (neutral molecules)to detect the actual activity. In the future, we want to have 10, 20 or even 30 channels to detect a broader range of plant VOCs.”
The team confirmed which combination of sensors worked most effectively to identify either a disease or an abiotic stress.
“Ultimately, we are trying to make it as straightforward as possible,” Wei said. “But growers will have to have some kind of user interface in order to save data.”
That may be information as straightforward as a plant being healthy or diseased. If infected, the farmer would need to know the kind of infection for them to take measures.
The next research stage is to make the patches wireless and test them on crops in the field. In real-world conditions, a new challenge includes the security of the sensors on the leaves when exposed to wind or rain.
Local farmers have already shown interest in the basic concept of the research, Wei said.
“They would just like to test the idea. It would be very interesting for them to grow some plants in soil and add nutrients. It would be a controlled environment for them with immediate applications. Industry has already shown interest, some in the technologies and some more interested in the information technology as a next step in commercialization. We have also talked to manufacturing to scale up production of the sensor device.”
Cost control is likely to be a major issue.
“For the current cost, it is quite cheap,” he said. “The patch is made of disposable polymer. Then there are the nano electronics and fabrication costs. Fine-tuning the technology will help to keep costs down.”
The unit cost for a sensor may be reasonable but the economics of using the sensors will depend on how many sensors a farmer would need and the labour cost for installation.
“The question will be how many sensors you will need for the size of farm,” he said. “We don’t have a good answer for that right now, but it is one of our major goals. However, for the new application, we don’t need a sensor for each plant, but we will be getting more information on this in the upcoming trials.”
A changing climate poses opportunities for the spread of new pathogens that would trigger a different host plant response. It will be important for more VOCs to be added to the patch so they can respond to many threats.
“The sensors can be used for many different scenarios, new stresses and high temperatures,” said Wei. “Because each stress will introduce a host plant response, the goal is to capture the message being sent by the plant so farmers can take appropriate action.”
The research was published in the journal Science Advances.
