Researchers Get Closer to Early Detection
Of HLB-Infected Citrus Trees
By Patrick Cavanaugh,
Using Volatile Organic Compound
sniffers with a suitcase-size gas chromatograph, and magnetic resonance
spectroscopy as well as DNA
sequencing of known huanglongbing (HLB)-infected citrus trees, scientists are
getting closer to a very early diagnosis that could help with early detection
and possible cures of the disease.
It’s all happening while
quarantines expand in the Central San Joaquin Valley after the HLB vector, the
Asian Citrus Psyllid (ACP), has been found on sticky traps or live in
trees. None of the collected ACPs have tested
positive for HLB. Still, the only known tree that has been positively infected
with HLB was a lone tree in a neighborhood in Hacienda Heights, near Los
Angeles, in March 2012.
“We are just verifying how
accurate these early detection techniques are, and it is being done by
scientists at UC Davis and UC Riverside,” noted Beth Grafton Cardwell, director of Lindcove Research and Education
Center, and research entomologist at UC Riverside.
The Citrus Research Board
focusing on a pre-systematic detection platform is funding all the work. The
tested plant tissue is from the infamous Hacienda Heights tree, the only known
tree in California ever to be infected with HLB. That tree was eventually
destroyed, but not USDA researchers took many samples.
Scientists are collecting
material from trees and testing with different antibodies and small RNA to determine
if these early detection systems really do work,” Mary Lou Pole, Vice President Science and Technology Citrus
Research Board, based in Visalia. “We have found some samples to be suspect-positive,
but the only way to confirm this is through the USDA’s PCR test, and of course
it comes up negative. And of course that’s the whole point of early diagnostics,
and that’s to pick it up before the PCR test.”
Some homeowners have actually
taken out about five trees, in total, after they were suspect with the early
diagnostics due to early Volatile Organic Compound (VOC) detection.
“The PCR test can only be
positive if it tests tissue where the bacteria is, which could be hit or miss,
so we are hoping to find a way to early-detect an infected tree with other methods,”
“Some other diagnostics
include host plant response proteins, which are secreted by bacteria that move
systemically throughout the tree,” Pole explained. “So, instead of looking for
the bacteria, we are looking for a signature of molecules associated with the
bacteria that is moving through the plant.”
“We are getting close to
finding a good way to detect early, and information should be coming in near
future,” said Carolyn Slupsky, UC
Davis Food Science Technology Associate Professor and Nutritionist. “We want to
know the metabolic pathways, the changes in the plant, before the plant starts
to yellow,” she said.
“Plants are always producing
metabolites, and an HLB infected tree will give off a certain pattern of
metabolites that can be detected by chemical analysis using magnetic resonance
spectroscopy,” Slupsky said.
“We are also working on
understanding when the pathogen infects the tree. Ultimately, we want to find a
way to kill the bacterial pathogen that causes HLB,” Slupsky said.
Diagnostic tools are being
developed that should help in the early detection.
Cristina Davis, professor in the UC Davis Department of Mechanical and
Aerospace Engineering, and Abhaya
Dandekar, professor in the UC Davis Department of Plant Sciences,
collected samples of VOCs emitted from HLB-infected trees in Florida every
month for a year in order to “train” the mobile sensor to recognize the “smell”
“The idea is to
extract a group of compounds that create the signature for the presence of
HLB,” Dandekar said. A software program develops an algorithm that lets the
machine know it is detecting HLB. Davis is working with Applied Nanotech, Inc.,
in Texas to commercialize this artificial nose.
Labels: ACP, Beth Grafton Cardwell, Carolyn Slupsky, Citrus Research Board, Cristina Davis, Early HLB Detection Sought, Mary Lou Pole, Researchers Get Closer to Early Detection of HLB-Infected Citrus Trees, VOC