By Sharon Durham
The pale potato cyst nematode (Globodera pallida) has been positively
identified by Agricultural Research Service (ARS) scientists and cooperators
in soil at a potato processing plant in eastern Idaho. This is the first
time this pest ? now of great concern in Europe ? has been found in the
United States.
The source of the infected soil at the processing plant was later
traced to a few potato fields in Idaho, according to the researchers with
ARS and the University of Idaho.

The ARS research team in Beltsville, Md., that performed the
identification included molecular biologist Andrea Skantar in the Molecular
Plant Pathology Laboratory; and microbiologist Zafar Handoo, plant
pathologist Lynn Carta, and research leader David Chitwood in the Nematology
Laboratory.

Handoo led the morphological identification, using microscopic
examination and measurement of anatomical features that are distinct for
cysts and immature juveniles of G. pallida. Skantar led the molecular
analysis, comparing DNA from the nematode specimens with known reference
material.

Existing molecular tests are very good at distinguishing G. pallida
from golden nematode (G. rostochiensis), due to previous research in Europe
where both species are found. However, scientists cannot readily use
anatomical differences to distinguish G. pallida from another close relative
called the tobacco cyst nematode (G. tabacum), a nematode already in the
United States. Reliable molecular tests to identify G. tabacum have not been
widely validated, largely because tobacco cyst nematode is not widespread in
Europe, where much of the prior research has been done.

Skantar developed a new diagnostic test that may become useful in the
future, as the national survey is conducted to determine the extent of the
potential spread of the pale potato cyst nematode. In the new assay,
specific PCR primers recognize minor differences in the DNA sequences of
each nematode species, resulting in a clear, positive test result when G.
tabacum is present.

Fields in the United States may include both G. pallida and G.
tabacum, so it is important to be able to tell these species apart. The new
test represents a proactive step aimed at preventing diagnostic confusion as
future identifications become necessary.

ARS is the U.S. Department of Agriculture's chief scientific research
agency.


[www.ars.usda.gov]