PORTABLE TESTER COULD HELP FARMERS QUICKLY STOP THE SPREAD OF PLANT DISEASE

Farmers could soon be able to identify plant diseases in the field using a handheld device which plugs into a smartphone.
Developed by researchers at North Carolina State University, the device works by sampling the airborne volatile organic compounds (VOCs) that plants release through their leaves.
“All plants release VOCs as they ‘breathe,’ but the type and concentration of those VOCs changes when a plant is diseased,” said assistant professor Qingshan Wei, who worked on the project.
“Each disease has its own signature profile of VOCs. So, by measuring the type and concentration of VOCs being released by the plant, you can determine whether a plant is diseased and - if it is diseased - which disease it has.
“Our contribution here is the creation of a device that can be plugged into a smartphone and used to make those VOC measurements quickly in the field.”
Current disease identification techniques rely on molecular assays, which take hours to perform and have to be carried out in a lab setting. Getting a sample to the lab, where the sample may have to wait to be tested, can delay disease identification by days or weeks.
“Our technology will help farmers identify diseases more quickly, so they can limit the spread of the disease and related crop damage,” said professor Jean Ristaino. “We are now ready to scale up the technology.”
To test their crops, farmers simply need to take a leaf from the relevant plant and place it in a test tube.
The test tube is then capped for at least 15 minutes to allow the relevant VOCs to accumulate. After this incubation period, the cap is removed and the farmer uses a narrow, plastic tube to pump the VOC-laden air into a ‘reader’ device connected to a smartphone.
The air is pumped into a chamber in the reader that contains a paper strip. The paper is embedded with an array of chemical reagents that change colour when they come into contact with a specific chemical group. By evaluating the resulting colour pattern on the strip, users can determine the nature of any plant disease that may be affecting the plant.

Organic dyes

Gold nano particles

“For this technology to work, we had to develop reagents that could be embedded in the paper strips,” said researcher Zheng Li. “About half of the reagents were off-the-shelf organic dyes, but the other half were gold nanoparticles that we functionalised to respond to specific chemical groups. These functionalised nanoparticles allow us to be more precise in detecting various types of VOCs.”

“We also had to design and build the reader device, since there is nothing like it on the market,” says Wei.
In proof-of-concept testing, the researchers demonstrated the device’s ability to detect and classify 10 plant VOCs down to the parts-per-million level.

They were able to detect the late blight pathogen that caused the Irish famine two days after tomato plants were inoculated with the pathogen.

Late blight on tomato leaf

Researchers could also distinguish tomato late blight from two other important fungal pathogens that produce similar symptoms on tomato leaves. In addition, the researchers showed they could detect the pathogen Phytophthora infestans in tomato leaves with greater than 95 per cent accuracy.

“We’ve shown that the technology works,” Wei said. “There are two areas where we could make it even better. First, we would like to automate the pattern analysis using software for the smartphone, which would make it easier for farmers to make disease determinations.
“Second, we envision the development of customised reader strips that are designed to measure the VOCs associated with other diseases specific to a given crop. Different crops in different regions face different threats and we could develop paper strips that are tailored to address those specific concerns.”