Spudman April 2023 - 9

Pictured is a micrograph of a stained
second stage juvenile of Globodera
pallida, but Globodera rostochiensis
cysts look similar to the naked eye.
Photo: Dandurand program at University
of Idaho
Cyst nematode trapped in a dying Solanum sisymbriifolium root cell. Photo: Dandurand
program at University of Idaho
nematodes are worrisome even though,
so far, they are much less widespread
than RKNs. The RKNs targeted for
research include the Columbia RKN,
Meloidogyne chitwoodi, and the
Northern RKN, M. hapla.
Creating new potato varieties by
genetic modification shows promise.
One project alters potato plants to
silence a particular nematode gene.
With the gene disabled, the worm
cannot parasitize the potato plant
effectively. Another genetic modification
induces the potato plant to make
toxins that poison the nematodes.
Boosting existing potato immune
responses may also increase nematode
resistance in potato. Apart from directly
modifying the potato, scientists test
natural substances that elicit plant
defenses. The latter may prove more
acceptable to consumers who are wary
of eating genetically modified food. So
far, all the above methods have shown
some success in reducing nematode
infections in potato plants.
The third prong of PAPAS research
is to develop one or more new
nematicides based on toxins produced
by Solanum sisymbriifolium, known
as litchi tomato, sticky nightshade, red
buffalo-bur and other common names.
In the same genus as potatoes, it is
currently used as a trap crop.
The way the trap crop
works is that the plants
produce chemicals that
induce the nematodes
to hatch, but the plants
also produce other
chemicals that inhibit
the worms.
The way the trap crop works is that
the plants produce chemicals that
induce the nematodes to hatch, but the
plants also produce other chemicals
that inhibit the worms. The nematodes
cannot reproduce and complete their
life cycle. If planted a season ahead of
potatoes, litchi tomato can reduce the
population of PCN's in the following
potato crop by up to 97%. Litchi tomato
does not provide an economic return to
the grower, though. Thus, the current
research is to purify and identify the
nematode-inhibiting chemicals, which
can lead to producing those chemicals
synthetically for commercial use.
In the meantime, potato growers
can take several steps to minimize
nematode damage. The first is to plant
certified seed, so as to not introduce
new nematodes to the farm. The
second is to monitor fields for patches
of plants showing stunting and
chlorosis, which may be symptoms
of nematode damage to plant roots.
Soil samples from those patches
should be sent to a lab for nematode
identification. Depending on the
state, the Cooperative Extension may
assist with soil sampling, such as
information, sampling boxes, transport
of the sample to the lab, diagnostics
and subsidized cost.
If the tests show the presence of
nematodes, the grower can apply a
nematicide. Next year, he or she can
choose to plant a resistant variety if
available, grow an antagonistic crop
or precede the potato crop with litchi
tomato as a trap crop. Finally, the
grower should be careful not to move
soil from field to field. As Dandurand
notes, " Any equipment entering a PCNinfested
field is power washed and then
sanitized before entering a different
field. " Boots should be cleaned as well.
TYPES OF NEMATODES
The nematodes afflicting potato
plants fall into four groups. Different
species prevail in different regions.
The first group is the potato cyst
nematodes, which are currently limited
in the U.S. to specific sites in Idaho and
New York. The cysts are visible to the
naked eye on the outside of the plant
roots as individual bumps, colored as
their names suggest: whitish for the
pale cyst nematode and gold for the
golden nematode. Resistant potato
Spudman.com 9
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Spudman April 2023

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