Dog noses are said to save the oranges

A beagle looks into a citrus tree. (Image: Gavin Poole)

Is this orange tree infected? Dogs can obviously smell that: Researchers have shown the potential of detection dogs in the fight against a devastating disease of citrus fruits. The four-legged plant protectors can identify affected plants by their smell at an early stage of infection, so that they can be removed from the stand to prevent spreading.

The fine nose of man’s best friend is legendary: Dogs have always tracked prey down on humans or made their owners aware of other smelling cues. The sensitivity of the animal smell system can still not surpass modern technology. For example, dogs still sniff trace substances or drugs hidden at airports. Even in medical diagnostics, the sniffers are used: Dogs have already been successfully trained to sniff out hidden infections or cancer in humans.

Against this background, the researchers led by Timothy Gottwald from the US Department of Agriculture in Fort Pierce have explored the potential of detection dogs in the diagnosis of herbal diseases. The focus was on a particularly insidious bacterial disease that is currently becoming a threat in the cultivation of citrus fruits. The so-called Citrus Greening or Huanglongbing is caused by the bacterium Candidatus Liberibacter asiaticus. The problem is that you don’t see an infection in the plants for a long time and the pathogen can spread unnoticed in the stand. But at some point all oranges, lemons and co shrivel – they become inedible and the trees eventually die. In this way, the disease devastates entire plantations and endangers billion-dollar orange cultivation, particularly in Florida and Brazil. In some regions, production has already dropped 70 percent.

The only chance: early detection of hidden infections

The only way to prevent the spread of the disease is to remove infected trees from the stands as quickly as possible so that they cannot infect healthy plants. Thus, an effective and at the same time less expensive method for early diagnosis is required. However, modern laboratory methods struggle with the timely detection of the disease, say the scientists. That is why Gottwald and his colleagues have now investigated the extent to which dogs are able to recognize the infection by the smell at an early stage. They missed 19 dogs a training, as it is used in the training of explosives detection dogs. The animals learn to report when they perceive a certain odorant. Then they will be rewarded.

As the researchers report, their experimental animals were actually able to develop a fine nose for citrus disease: “It turned out that these dogs were able to identify infected orange trees with the pathogen within two weeks after inoculation after training,” says Gottwald , The successful sniffing rate is an impressive 99 percent, the scientists report. As tests on other plant species infected with the pathogen showed, the animals apparently react to an odorant that the bacteria themselves produce and not to substances in the infected plants. The dogs were also able to distinguish the citrus greening pathogen from a variety of other bacterial, viral and fungal diseases, the studies showed.

Detectors beat laboratory detection methods

The researchers also clarify that the performance of the current laboratory method for detecting the disease is significantly lower than the success of the sniffers. The DNA-based detection methods were only able to detect three percent of the diseases two months after the experimental infection with the pathogen. 17 months after infection, the laboratory tests were able to identify 20 out of 30 diseased trees. This shows that the dog’s nose is clearly ahead. In addition, the genetic detection procedures require considerable time, financial and human resources. In contrast, you only need to walk through the plantation with the sniffer dogs in the animal diagnostic procedure.

“When we carried out epidemiological simulations, it became clear that detection by dogs in combination with the removal of the infected trees from the citrus industry over a period of ten years can again enable economic sustainability,” says Gottwald. Again, the dogs could prove to be best friends of humans – in this case, best friends of the citrus farmers.

Source: US Department of Agriculture – Agricultural Research Service, Technical article: PNAS, doi: 10.1073 / pnas.1914296117

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