New research on the microbial
cause of Pierce's disease should enable grape growers to protect vineyards and
produce top-quality grapes, such as this ARS-developed seedless variety, Autumn
Royal. Click the image for additional information about
Examining the Many Faces of
December 18, 2003
Thousands of southern California grapevines were wiped out
several years ago by a devastating affliction known as Pierce's disease. The
disease is the work of a microbe called Xylella fastidiosa (pronounced
ZYE-lell-uh FAS-tid-ee-oh-suh). Harmless to humans, X. fastidiosa is
carried from one grapevine to the next by insects such as the glassy-winged
But it's not just grapevines that are beleaguered by X.
fastidiosa and sharpshooters. The microbe occurs in many forms, or strains,
that sicken other plants, including almond, citrus, peach, plum and
Service experts at the agency's San
Joaquin Valley Agricultural Sciences Center at Parlier, Calif., are sorting
out who's who in the world of Xylella. They're doing that by comparing
the microbes' genetic material, or DNA.
Molecular biologist Jianchi Chen is developing a DNA-based test
that would determine which strain of Xylella--if any--certain plants are
harboring or specific insect pests are carrying.
Results of the DNA test could give growers of vulnerable plants
a valuable heads-up. In addition, the assay would give agricultural inspectors
a fast, accurate way to make sure that shipments of plants for commercial
orchards or backyard gardens are free of Xylella. Currently, plants
sometimes have to be monitored for weeks or even months to be certain they're
Chen and his colleagues in the ARS Exotic and Invasive Diseases
and Pests Research Unit at Parlier--plant physiologists Hong Lin and Fred Ryan
and entomologists Elaine Backus and Russell Groves--are each pursuing unique
investigations of Xylella, the sharpshooters that spread it, and the
diseases it causes.
ARS is the U.S. Department of
Agriculture's chief scientific research agency.