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Globodera pallida cysts
Globodera pallidacysts. Cysts are the egg-engorged bodies of dead female nematodes. Eventually, the cysts dislodge from a plant root and the eggs hatch. Image courtesy Zafar Handoo,ARS.

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ARS Scientists, Cooperators Identify Potato Pest

By Sharon Durham
June 27, 2007

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.