April 2019 - 37

complete resistance to the species
and pathotypes of Globodera that
are present, as well as to those which
could be introduced. Resistant sources
are limited, but the Globodera spp.
threat to the potato industry would be
greatly
reduced
if
varieties existed with
resistance to all three
cyst nematodes,
G.
pallida,
Over the years,
efforts to incorporate
a
(H1)
resistance
into
gene
potatoes
has produced many
G. rostochiensis
resistant varieties.
This gene is very effective for nematode
races
Globodera pallida cyst full of eggs.
Pyramiding
or stacking
resistant
genes from more than one source can
increase the level of resistance in an
additive or synergistic fashion.
Resistant potato populations
have been developed that combine
different
sources
of resistance (those
QTLs
earlier).
G.
rostochiensis and G.
ellingtonae.
mentioned
Varieties
from these crosses,
with
pyramided
genes for G. pallida
and G. rostochiensis
resistance, can be
used as a sustainable
method to reduce
and help eliminate
nematodes
in
infested soil. Some
(pathotypes) Ro1 and Ro4. A
resistance scale ranks a potato variety
from 1 (no resistance) to 9 (high
resistance). Using this scale, many
resistant varieties with the H1 gene come
in at a 9. This is major gene resistance
and it is inherited in a simple, dominant
fashion.
Fortunately,
our GLOBAL
group has determined that any potato
variety that has the H1 gene also has high
resistance to G. ellingtonae.
Success in controlling G. rostochiensis
races Ro1 and Ro4 has been achieved
using varieties carrying the H1 gene.
However, use of these varieties has,
over time, revealed that some G.
rostochiensis populations contain
another race, Ro2, that is not controlled
by this gene. Ro2 has become an issue in
New York and some European countries
where H1 resistance is frequently used.
Resistance to G. pallida has been
found in a few sources, including
Solanum vernei, a wild potato species,
and S. tuberosum subsp. andigena,
a cultivated Andean sub-species.
Resistance from these sources has been
transferred into a few commercial
varieties. However, the resistance
is not based on major genes, but on
contributions
from multiple
genes,
each of relatively small effect. These
genes are also known as minor genes
or Quantitative Trait Loci (QTLs).
Resistance against G. pallida is not
as effective as resistance the H1 gene
confers against G. rostochiensis.
varieties developed may be resistant to
G. pallida and not G. rostochiensis or
vice versa.
LIMITING PCN SPREAD
Regulatory measures in New York have
limited the spread of G. rostochiensis;
and the nematode remains contained.
Use of resistant varieties, introduced in
the 1980s, greatly benefited growers in
New York so they could return to potato
production with regulatory oversight.
Extensive sampling of Idaho fields since
2006 has shown that the G. pallida
infestation is limited. The quarantine
measures taken have allowed the U.S.
and Idaho to regain important foreign
markets that initially closed because
of the nematode. Eradication efforts
for G. pallida in Idaho are ongoing
with the goal to return fields to normal
production. These efforts include
fumigation, extensive sampling and a
core set of parameters to be met before
a field is released for potato production.
The
goal to
develop resistant
varieties will ultimately help in
eradication of PCN. More time and
resources are needed to develop
varieties with high resistance to G.
pallida and G. rostochiensis (Ro1 and
Ro2) as well as G. ellingtonae. The
GLOBAL group has made progress in
achieving broad resistance to potato
cyst nematodes with our efforts
being a component of an integrated
approach for the management of these
destructive pests of potato.
Spudman * April 2019
37
April 2019

Table of Contents for the Digital Edition of April 2019
