Test Detects Insect Carriers of Citrus Greening
By Marcia Wood
October 23, 2009
With their pleasing flavor, cheerful
color, and health-imparting dose of vitamin C, it's not surprising that oranges
are one of America's Top 10 favorite fruits. But some of the nation's citrus
groves are threatened by a microbe that causes citrus greening disease, and by
a tiny insect that carries this microbe.
To help protect citrus, Agricultural
Research Service (ARS) plant pathologists
F. Lee and
L. Manjunath developed a test that reveals whether tiny insects called
Asian citrus psyllids are in fact carrying Candidatus Liberibacter
asiaticus, one of three microbial species thought to cause the disease.
Developed over the past several years and reported in a 2008 article in the
the test is being used today by plant health officials in the United States and
Assaying psyllids may provide a way to detect citrus greening disease up to
two years before symptoms become apparent in afflicted plants, according to the
scientists. They're based at the ARS
Clonal Germplasm Repository for Citrus and Dates in Riverside, Calif.
First detected in the United Statesin Floridain 2005, citrus
greening or citrus Huanglongbing disease (HLB) has already infected millions of
citrus trees in that state, and has also shown up in Georgia, Louisiana and
Though not the first to detect HLB in Asian citrus psyllids, the assay
apparently still is one of the newest of its kind to be based on what's known
as "real-time qPCR" (short for "quantitative polymerase chain
reaction") technology. The test is comparatively quick and relatively
inexpensive, and can be performed by technicians working in any of the labs
across the country that already handle PCR assays.
The scientists have used the assay to test more than 10,000 psyllids,
Diaphorina citri, collected from orchards, backyards, retail nurseries
and other venues in Florida where citrus plants are grown or sold.
The assay is one of the many accomplishments from ARS research laboratories
nationwide that strengthen international food securitya top priority of
the U.S. Department of Agriculture.
more about the research in the October 2009 issue of Agricultural
ARS is USDA'S principal intramural scientific research agency.