By Sharon Omahen
University of Georgia
Using DNA technology, University of Georgia scientists are
working to develop a quicker, easier way to detect pathogens on
plant seeds.
“We started this project in light of our nation’s concern over
biosecurity in agriculture,” said Ron Walcott, a plant
pathologist with the UGA College of Agricultural and
Environmental Sciences.
“Our goal is to develop a system that can detect pathogens in
seeds,” Walcott said, “whether they were put there intentionally
or unintentionally during the seed production process.”
Funded by USDA grant
Iowa State and Clemson scientists will work with Walcott on the
four-year project. The U.S. Department of Agriculture National
Research Initiative’s Animal and Plant Biosecurity Program will
fund it with a $900,000 grant.
“Seeds for our country’s food crops are produced around the world
in various countries, including Thailand and China,” Walcott
said. “Then they’re shipped and sold in the United States. Hard
labor is still heavily involved (in seed production), so there
are always risks of introducing exotic pests.”
The current methods used to screen seeds for fungi, bacteria and
viruses can take weeks. The researchers’ goal is to develop a
quicker, more accurate and precise testing method.
New method will be quick, effective
“As an example, one of the currently employed tests requires that
seeds be planted and grown out to determine if a pathogen is
present,” Walcott said. “This is time-consuming. And
unfortunately, this test is expensive to conduct. And there’s a
risk of failure, depending on the level of seed infestation.”
With current methods, he said, it could take weeks to develop a
technique to detect a new pathogen suspected to be intentionally
introduced into the nation’s seed supply.
“If it were a case of bioterrorism, we’d need to know as soon as
possible,” he said. “We have a lot of techniques available now,
but the methods are neither effective nor reliable.”
Scientists now use up to five tests to detect different
pathogens, he said. A goal of this project is to develop one test
that would be used to detect all seed pathogens.
Uses DNA and RNA technology
The new detection method will rely on both DNA and RNA to find
out whether pathogens are present.
“Plants have DNA just like we do, but some viruses have only
RNA,” Walcott said. “The plan is to use a technique called
magnetic capture hybridization to capture and detect the presence
of pathogen DNA/RNA in a seed sample.”
DNA and RNA are the molecules that encode an organism’s
physiological characteristics. These codes include sequences
unique to the organism.
“By relying on specific DNA or RNA sequences, highly specific and
sensitive detection assays can be developed,” Walcott said. “As
such, this approach is highly applicable for the detection of low
levels of pathogens in seeds.”
To apply this technique, scientists crush a sample of seeds and
mix crude nucleic acids from the seed extract with magnetic,
polystyrene beads.
Just like fishing
The beads are coated with single-stranded DNA, which hybridizes
or binds specifically to the pathogen’s DNA. The scientists
recover the beads with a magnet, then amplify the DNA by
polymerase chain reaction.
“It’s like fishing, but we use mirror-image DNA instead of night
crawlers as bait,” Walcott said. “This method is highly sensitive
and efficient and can work for a wide range of seeds and
pathogens. Most important, the turnaround time is just a day.”
As a starting point, the research team is focusing on two
watermelon diseases that Georgia growers fight: bacterial fruit
blotch and gummy stem blight. The next phase will include
detecting diseases of tomato, onion, wheat, corn and soybean.
“Once we have the system going, we will have the capability to
detect more seedborne pathogens,” Walcott said. “If a new one
that’s not in our database is introduced by terrorists or Mother
Nature, it will just take a couple of days to add it to the
system.”
