Researchers developed quick diagnostic tests to detect Phytophthora infestans

By Jorge Luis Alonso G., an information consultant specializing in potatoes

A North Carolina State University team has developed quick diagnostic tests to detect plant diseases before they show symptoms in the field. In particular, they have worked on technology for identifying Phytophthora infestans, which causes late blight in potatoes and tomatoes. This article highlights how that technology works and describes the benefits for producers.

Potato was the most widely grown crop in Ireland in 1845 when late blight arrived. The disease wiped out half of the potato crop that year and about three-quarters of the crop for the next seven years. As a result, about one million people died, and a similar number had to emigrate to other latitudes.

Today late blight is still one of the most destructive diseases of tomato and potato. Globally, economic losses approach US$6 billion each year. Due to its rapid rate of spread, this disease poses a significant threat to food security around the globe.

Although some countries have implemented decision support systems and other tools to manage late blight, smallholder farmers in lower-income countries continue to use fungicides to control this disease at a high frequency. Excessive fungicide use increases production costs and creates severe risks to the environment and the farmers and families. In these areas, chemicals are almost always applied without adequate protection.

Detection Technologies

When a technician suspects a disease, he has to go to the field, get a sample, bring it into the laboratory, and wait for isolation of the microbe in culture or DNA analysis. The diagnosis can take days to weeks.

NC State University has created the Emerging Plant Disease and Global Food Security Cluster to mitigate the problem. The cluster focuses on emerging plant diseases that threaten food security, and work began with Phytophthora infestans and several other bacterial, fungal and viral diseases of tomatoes.

Specifically, the NC State team developed three in-field sensors. The first two sensors, a paper strip and a chemiresistor, detect volatile organic compounds (VOC). VOC are chemical signals emitted by the plant’s leaves when a disease stresses them. In other words, when a plant becomes infected by a pathogen or an insect pest, it releases a profile of compounds. And these compounds, the VOC, are signatures of infection. So sensors can read the volatile signature and identify the pathogen before symptoms occur.

The difference between the paper strips or chemiresistor sensors is that the latter allows continuous monitoring in real-time and remotely. “The paper strip is only good for point measurements, which requires more human intervention,” says Qingshan Wei, North Carolina State researcher and corresponding author of all three papers.

“The VOC methods (paper strip or chemiresistor) are noninvasive and so more rapid. But they may have limitations in sensitivity and specificity when compared to the conventional molecular methods”, said Dr. Wei.

The third sensor uses a micro-needle patch to isolate DNA, which is then used to identify the pathogen causing the infection. “Molecular diagnostics via the micro-needle patch are the most accurate and sensitive,” Dr. Wei concluded. “It is also more like to the current standard, the PCR* method in the laboratory.”

The selection of a particular method will depend on the urgency and accuracy of the diagnosis required.

All information is collected wirelessly from the sensors on smartphones and stored in databases to alert growers of new outbreaks. The databases can also be used by researchers to model disease spread for a more effective, rapid response.

The sensors can detect pathogens of other crops or even detect human and animal foodborne diseases, as well as insect pests.

* Polymerase Chain Reaction

Smartphone sensor ‘sniffs out’ plant infections (Qingshan Wei)

Managing Emerging Plant Diseases

Interest in these devices has heightened as people have become more aware of the science of epidemiology within the context of the current human pandemic. As noted in a recent perspectives article on the “Persistent Threat of Plant Diseases” by the National Academy of Sciences (NAS), “Humans are not the only creatures affected by a pandemic; plants can be too, and that could threaten the world’s food supply.”

This paper stresses the importance of having better tools to detect, track and stop plant disease outbreaks. Also, it makes a variety of suggestions on how to follow the transmission of plant pathogens.

The plan is to “detect these plant disease outbreak sources early and stop the spread before a full pandemic occurs,” says Jean B. Ristaino, cluster director and senior author of the PNAS paper. “Once an epidemic happens, it is hard to manage”, she said, comparing the work done so far to stop the expansion of COVID-19.

The Benefits for Producers

“In wealthier countries, such as the US and Europe, large and small producers could benefit from these technologies to verify early diagnoses of important diseases, which would allow timely and more efficacious implementation of control measures,” suggested Greg Forbes, a retired plant pathologist who had worked for 29 years at the International Potato Center. “These technologies could also be used to identify emerging pathogens that pose new threats to commercial crops and wild plant species, and thus help avoid diseases of pandemic scale”.

Forbes added “As these technologies only need smartphones and telephone networks, which have now become virtually universal, the sensors and data networks could also be used in lower-income countries where they could be of value to producers and those working in agricultural extension. Farmers in these countries generally cannot afford the sophisticated equipment needed for other types of decision support systems”.    

Final Words

All these technologies have pending patent applications.

“The commercialization of the micro-needle technology may be faster, as the system is less complicated and several big Ag companies have contacted us,” says Dr. Wei. But the wearable sensor may take a little bit more time. “Several issues need to be solved for the wearable sensor before field deployment, such as power supply, wireless data connection, etc.,” he added.

In the meantime, the Emerging Plant Disease and Global Food Security Cluster will continue working with tomato late blight in the next phase. Still, the North Carolina Plant Science Initiative (PSI) recently funded its team to test the sensor technologies to detect other plant diseases (early blight, bacterial spot, and tomato spotted wilt virus). Shortly, they hope to test the sensors on other plants, including potatoes.

If you want more information about the technology, you can request it from Dr. Qingshan Wei at qwei3@ncsu.edu.

Author: Jorge Luis Alonso G. is an information consultant specializing in the potato crop. He writes marketing materials for Ag-Tech companies. The article above was written exclusively for Potato News Today.