Trained Dogs Are the Most Efficient Way to
Hunt Citrus Industry's Biggest Threat
By Kim Kaplan
February 3, 2020
February 3, 2020
FORT PIERCE,
Florida, Feb. 3, 2020—Dogs specially trained by
Agriculture Research Service (ARS)
scientists have proven to be the most efficient way to detect
huanglongbing—also known as citrus greening—according to a paper just published
in the Proceedings of the National Academy of Sciences.
Currently, the only solid
hope of curtailing the spread of citrus greening is to eliminate trees with the
disease as quickly as possible to prevent further spread. Early detection of
the citrus greening pathogen is crucial because trees can be infected and act
as a source to spread the disease months or years before showing symptoms that
are detectable by the naked eye.
ARS plant epidemiologist Timothy R.
Gottwald with the U.S.
Horticultural Research Laboratory in Fort Pierce, Florida,
discovered that dogs can be trained to sniff out the presence of Candidatus Liberibacter asiaticus, the
bacteria that causes citrus greening, with greater than 99 percent
accuracy.
"We found that, once
trained, these dogs were able to identify infected trees within two weeks of
the trees being inoculated," Gottwald said. "The dogs also were able
to distinguish the citrus greening pathogen from a variety of other citrus
bacterial, viral, fungal, and spiroplasma pathogens, including closely related
Liberibacter species.
During testing, the citrus
greening detector dogs had total of 4 to 15 false negatives and false positives
on 950 to 1,000 trees per dog. Occasionally, the dogs alerted on clean trees
that were in the same spot where an inoculated tree had been placed in previous
tests due to residual scent.
In contrast, the only
currently USDA-approved method for confirming the presence of the citrus
greening pathogen—a DNA-based assay called a polymerase chain reaction (PCR)
test detected less than 3 percent of infections at 2 months, 16 of 30
inoculated trees at 16 months, and 20 out of 30 in 17 months.
PCR tests also require
considerable time, financial and human resources for sampling, processing and
laboratory work. They are very expensive to use as a general surveillance tool.
The training is similar to
that of explosives sniffing dogs, in which the dogs are taught to recognize a
particular odor and to sit down next to the source once found. The dogs are
rewarded with play time with a toy. However training is more extensive
and specific because the dogs are trained to detect a bacteria infecting a plant,
and the two cannot be separated.
So far, Gottwald's program
has trained 19 dogs obtained from European breeders of detection canines
because of their keen abilities and drive. (Watch a video)
"When we ran
epidemiological models, we found canine detection combined with infected tree
removal would allow the citrus industry to remain economically sustainable over
a 10-year period, compared to using molecular assays or visual inspection
combined with tree removal, which failed to suppress the spread of
infection," Gottwald explained.
Citrus green sniffing dogs
have been deployed for 9 months in California and northern Florida.
In the past decade,
huanglongbing has caused more than 70 percent decline in the production of
oranges for juice and the fresh fruit market in Florida and threatens other
states, making it the largest economic threat to the $3.35 billion U.S. citrus
industry. It was first found in the United States in 2005, citrus greening has
spread to Florida, Texas, California, Georgia, and Louisiana.
