Just by sniffing the air, an electronic nose can tell when cucumber and capsicum pepper plants are damaged - and even diagnose the problem.
The gadget can distinguish the whiff of a plant covered with caterpillars from one plagued with mites, or just physically damaged. It could act as an early warning system in glasshouses, alerting farmers to the early signs of disease before crop yields fall.
An electric nose contains a small number of sensors that can each bind to the airborne chemicals that make up a smell. This changes the way a sensor conducts electricity, and each sensor responds to the same compounds in different ways. The combined response of the sensors can thus vary greatly with each individual smell.
Now biologists at Lancaster University, UK, have shown electronic noses can diagnose diseased or damaged plants as well. Plants naturally emit a cocktail of volatile organic compounds (VOCs) that changes subtly when they are under attack.
Nigel Paul knew that some insect predators can use those signals to detect pests that make a good meal. He wondered whether an electric nose could discriminate between VOC cocktails too.
His team grew cucumbers, capsicum peppers and tomatoes in a glasshouse for five weeks, before placing hungry tobacco hornworm caterpillars or spider mites on their leaves. Some plants were instead physically damaged using a hole punch.
A Bloodhound electronic nose, supplied by Scensive Technologies in Normanton, UK, was used to analyse the air stream flowing over each group of plants.
Results showed that the electronic nose could distinguish the healthy aromas from each of the three species of plant. More impressively, it could distinguish whether a plant had been attacked by a hole punch, caterpillar, or mite.
"The instrument we used was an 'untuned system' - it hadn't been modified to be especially sensitive to particular volatiles," Paul told New Scientist. "That's what makes our results so encouraging, that even this very basic system worked well."
The team also used gas chromatography-mass spectroscopy to identify exactly which chemicals were released by the plants. The results will be used to fine-tune the nose and get even better diagnoses in future.
The exact sensitivity of the nose has not yet been measured. "But the nose did pick up what must have been very dilute signals in a fast air flow," Paul says, and improvements in electronic nose design over the two years since the study began could make the device even more sensitive.
"We have been looking at the same problem," says Julian Gardner at the University of Warwick, UK. "The possibility of detecting plant volatiles using electronic noses is quite feasible. It is an exciting area of study and offers great possibilities in helping the plant industry."
Paul says that a number of electronic noses could be dotted around a glasshouse, checking the air for the early signs of pest attack. Portable electronic noses - about the size of a four-pack of beer - could be used to precisely locate infected plants.
Journal reference: Environmental Science and Technology (DOI: 10.1021/es801738s)
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