Potato Cyst Nematode - Diagnostic Services

Diagnostic Facts
Diagnostic Services
Michigan State University
MSU-DS26
www.pestid.msu.edu November 2008
Potato Cyst Nematodes:
Serious Threats to Michigan’s Potatoes
Fred Warner
Diagnostic Services
Introduction
Potato cyst nematodes are considered the most economically important nematode pests of potato and are
the subject of strict regulations and quarantines in many countries. Fortunately, these nematodes have not
yet been detected in Michigan. However, any detection will have undesirable short and possible long term
impacts on our state’s potato
production, especially export of
seed. To minimize the spread of
these nematodes, potato fields,
particularly seed potato fields,
should be sampled on a routine
basis.
The cultivated potato, Solanum
tuberosum spp. tuberosum, is host
to approximately 70 species of
plant-parasitic nematodes. One
species in particular, Pratylenchus
penetrans, a root-lesion nematode,
impacts potato production in
Michigan due to its role as a
pathogen and predisposition
agent to the fungus, Verticillium
dahliae. Many potato growers
in Michigan routinely collect
Field infected with Potato Cyst Nematode.
samples the fall before potatoes
are grown to assess population
densities of P. penetrans and
V. dahliae. Diagnostic Services at MSU receives between 500-1000 samples annually for nematode analyses
and Verticillium assays. This volume represents approximately 40% of Michigan’s annual 45,000-50,000 acres
of potatoes.
History
For many years, only one
species of potato cyst nematode
was recognized, Heterodera
rostochiensis. However, H.
rostochiensis was later separated
into two species, H. pallida with
white or cream-colored females,
the pale potato cyst nematode
(wPCN) and H. rostochiensis with
golden females, the golden potato
cyst or golden nematode (PCN).
White cysts on infected roots. Each cyst contains 200-500 eggs.
Eventually, these nematodes were
given the genus name Globodera.
Globodera sp. have round cysts
whereas, Heterodera sp. produce lemon-shaped cysts. Michigan is home to at least 6 species of Heterodera but
no Globodera.
It is generally accepted potato cyst nematodes originated in the South American Andes where they coevolved
with their preferred host, the potato. They are found in many temperate regions of the world infesting
approximately 65 countries. In the United States, golden nematode (PCN) was detected on Long Island, NY
in 1941 and in 1967 in Steuben County, NY. The first detection of the pale potato cyst nematode (wPCN) in
the U.S. occurred in 2006 when this pathogen was found in soil collected from a packing shed in Idaho. The
detection ignited a national voluntary survey, initiated in 2007, of all potato producing states in the U.S. In
addition to the recent detection(s) in Idaho, PCN was found in Quebec and Alberta Provinces, Canada, in 2006
and 2007 respectively. PCN and wPCN had previously been reported from Newfoundland in 1962 and PCN on
Vancouver Island in 1965.
Biology and Life Cycle
Potato cyst nematodes overwinter as eggs within cysts in the soil. In the
spring, second-stage juveniles (J2s) hatch from the eggs, exit the cysts
and enter hosts just behind the root tips. These young nematodes move
toward the vascular tissue and ultimately establish feeding sites. Soon
after they initiate feeding, they begin to swell and become sedentary.
If large feeding sites are successfully established, the nematodes will
eventually mature into females. If the feeding sites are smaller, males
result. Females become large enough to rupture through the epidermis of
roots and are exposed to the soil. At this time, if potato plants are gently
dug from the soil, so feeder roots remain intact, females can be seen with
the naked eye. They are white to yellow in color and about the size of the
head of a straight pin. Males mate with the females, the result being the production of 200-500 eggs retained
inside the females’ bodies. Roughly, 40 days are required to go from egg to adult but this is dependent upon soil
temperature. In the absence of a host, roughly 33% of the eggs hatch every year with some remaining viable up
to 20 years. In the presence of a host, 60-80% of the eggs hatch.
Eggs within cysts can persist for long periods in the soil and they withstand desiccation very well. Cysts can
persist and survive on the surfaces of tubers as well as equipment. It is speculated the initial infestation on Long
Island resulted from cysts adhering to military equipment employed during World War I and subsequently used
in potato production.
Host Range
Potato, tomato and eggplant are the only commercially grown crops parasitized by PCN. Potato is favored.
Many weeds in the genus Solanum and four wild species of Lycopersicon support some reproduction of PCN.
Plants in 6 or 7 other genera are also regarded as hosts; all these are weeds or ornamentals.
Comparison of healthy potato plant (on left) and infected plant (on right).
Diagnosis and Sampling
Neither species of potato cyst nematode have been detected in Michigan at this time. Therefore, it is unlikely
potato or tomato crops will exhibit symptoms of parasitism by these pathogens. If either species is accidently
introduced into a potato field, it is likely no symptoms will be visible for 6-8 potato crops. However, once
symptoms occur, significant crop losses will ensue. Many species of cyst nematodes reduce yields prior to the
production of any above-ground visible symptoms.
To export seed potatoes to Canada or other countries, sites must be certified free from both species of potato
cyst and other plant-parasitic nematodes as specified by USDA-APHIS-PPQ. This agency has released Potato
Cyst Nematode National Survey and Diagnostic Cyst Sample Forwarding Protocols that must be followed in
order to declare field sites free from PCN and wPCN. These sampling protocols are very intensive. For instance,
every acre of a seed potato field must be sampled in accordance with these protocols. Each sample will be
comprised of at least 100 subsamples (soil cores). The entire soil sample must be processed for nematodes. If
the sample is free from nematodes of regulatory significance, a phytocertificate can then be issued for export. Plant-parasitic nematodes are much easier to manage if infestations are detected early. Commercial potato
growers, especially those who have recently purchased seed from Alberta, should sample their fields for PCN.
PCN can survive on the surfaces of tubers and seed is the principal source of dissemination into other fields.
Conclusion
Steps should be taken to avoid potato cyst nematodes for as long as possible. Quarantine programs implemented
after the detections in NY have been quite successful but further spread of these nematodes appears imminent.
Early detection is critical to reduce their spread and impact. For this reason, all Michigan potato growers are
urged to sample for PCN and wPCN on a regular basis. In some situations, it will be mandated for regulatory
purposes.
If you have questions or concerns regarding potato cyst or any other plant-parasitic nematodes, feel free to call
Fred Warner (517-432-1333), Angela Tenney (517-353-8563) or Dr. George W. Bird (517-353-3890) at MSU.
Crushed cyst containing eggs and J2s.
Golden Nematode - adult females and cysts.
Photo courtesy Canadian Food Inspection Agency
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