Team to Make Plant Disease Diagnosis Faster, Easier and More Accurate
November 29, 2001
When it comes to fighting crop
diseases, field surveillance also has its place on the front lines of farming.
That's why Agricultural Research Service
scientists and Cepheid, a
Sunnyvale, Calif., company, are collaborating on tests of portable, DNA-based
devices that will identify plant disease organisms in less than 60 minutes
versus days or weeks by traditional methods.
Rather than await results from diagnostic labs using such methods, for
example, Extension Service agents could make on-site, "real-time"
recommendations on how best to curtail a crop disease outbreak before it
spreads further. Another foreseeable use is checking perishable plant materials
at ports of entry for exotic plant disease organisms that could imperil
domestic crops, notes Norm Schaad, with ARS'
Exotic Diseases-Weed Science
Research Unit, Frederick, Md.
Along with ARS lab associates Reid Frederick and Vern Damsteegt, Schaad is
collaborating with Cepheid under a cooperative research and development
agreement (CRADA) with ARS. Cepheid's portable
Smart Cycler unit, which connects to
a laptop computer, uses polymerase chain reaction (PCR) to replicate a target
pathogen's DNA--its unique genetic fingerprint.
The ARS scientists are using their expertise in bacterial, fungal, and viral
genetics to design primers and probes targeting specific DNA sequences of
several major plant pathogens. The primers main job is to bind with a
pathogens DNA--if present in a leaf sample, for example--and prepare it
for PCR amplification on the testing unit. The amplified DNA also binds with
the probe, emitting a flourescent signal at the end of each PCR amplification
cycle thats measured and displayed on the computer.
For bacteria, users need only immerse infected tissue specimens in water for
20 minutes before placing a microliter sample of it into one of the unit's 16
reaction chambers--no DNA extraction is necessary.
The ARS scientists will share data from lab and field tests of the Smart
Cycler using ARS primer/probes for Pierces disease, citrus canker,
watermelon fruit blotch, bacterial wilt, brown rot of potato, potato ring rot,
Karnal bunt, soybean rust, plum pox and other diseases. Under the CRADA,
Cepheid has first rights to commercialization of primers and probes for these
ARS is the U.S. Department of
Agriculture's main scientific research agency.