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Plant Protection Today - This USDA Lab Detects the Invisible

This USDA Lab Detects the Invisible
October 28, 2021

Protecting American Agriculture at the Molecular Level

PPCDL scientist Tanisha Robinson-McKenzie conducts confirmatory diagnostics of imported solanaceous (tomato & pepper) seeds.

By April Dawson

This month Plant Protection Today continues its Science and Technology (S&T) laboratory article series by spotlighting the Plant Pathogen Confirmatory Diagnostics Laboratory (PPCDL), formerly known as the Beltsville Lab, located in Laurel, MD.

Every day our scientists and technical professionals apply their expertise to safeguarding agriculture and facilitating safe trade. “Timely, accurate diagnostics is critical in detecting plant pests early and responding rapidly,” said PPCDL Lab Director, Mark Nakhla. “That helps us contain, suppress, and—when warranted—eradicate exotic pests to safeguard U.S. agriculture and natural resources. It also means saving the livelihoods of our farmers by keeping foreign export markets open to our agricultural products and protecting our natural environment.”

As its name suggests, the S&T PPCDL works with plant pathogens such as bacteria, fungi, oomycetes, viruses, and viroids. These microorganisms are not easily identifiable by the naked eye or light microscope, thus requiring sophisticated molecular tests that detect unique parts (fingerprints) of the genomes or proteins of these organisms.

As Nakhla often says, “We protect American agriculture at the molecular level.” The lab fulfills its mission by providing timely and accurate diagnostics to multiple programs and initiatives of the U.S. Department of Agriculture’s Plant Protection and Quarantine (PPQ). Its experts develop new diagnostics tools (methods) released in a form of specific documents called Work Instructions (WI) for regulated pathogens. They also produce Proficiency Tests (PT) panels for annual certification of plant health diagnostic laboratories under the National Plant Protection Laboratory Accreditation Program (NPPLAP). All of this is accomplished under a quality management system to secure the highest possible confidence in diagnostic results. In fact, the lab has earned ISO17025:2017 accreditation and is the only Federal plant pathogen diagnostic lab that holds it.

PPCDL routinely conducts federal confirmatory diagnostics for around 12 different pathogens on citrus, vegetables, stone fruit, nursery plants, and seeds. Most of the time, the lab tests pre-screened samples from planned surveys or activities. But sometimes, the diagnostics involve plant health emergencies, including recent ones such as Ralstonia (read the Plant Protection Today story).

Diagnostic results are the key in confirming the presence of a plant pathogen. Then PPQ can take the regulatory actions necessary to prevent the introduction of the pathogen on plant material imported into the United States or begin surveying to determine how widespread the plant pathogen may be. When overseas vendors sent unsolicited seeds to internet shoppers all around the country, PPCDL utilized a very powerful new technology called High Throughput Sequencing (HTS) to find whether any potential harmful pathogens were present in these samples.

“The PPCDL is instrumental in maintaining a network of more than 30 diagnostic labs from PPQ, the National Plant Diagnostic Network, State departments of agriculture, and third-party labs to provide diagnostic capacity for PPQ,” says S&T Associate Deputy Administrator Wendy Jin.  “The laboratory provides annual trainings, diagnostic protocols, and reaction controls for testing of thousands of samples collected each year for various PPQ programs.”

[Photo: A PPCDL scientist conducts a real-time High Throughput Sequencing analysis on a portable, third-generation sequencer.]

A PPCDL scientist loads plant test samples into a freeze-dryer to produce Proficiency Tests panels, which PPQ uses as part of a lab accreditation process.

To increase stakeholder confidence in the diagnostic results and ensure quality of diagnostic testing, the PPCDL supports the NPPLAP accreditation and certification process. The lab produces more than 100 PT panels every year. These panels are used to evaluate technical competency and certify diagnosticians from diagnostic laboratories for conducting testing for Huanglongbing, Phytophthora ramorum, and plum pox virus.

In the last decade, thanks to the scientific expertise and technical capacity of their scientists, the PPCDL has completed confirmatory diagnostic tests for thousands of samples, produced over 150 Work Instructions (protocols), and trained and provided PT panels to hundreds of diagnosticians across the country. The key to the lab’s success lies in dedicated staff who are committed to applying the best science in support of PPQ’s mission.

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