Agriculture Reference
In-Depth Information
or maintain PPN numbers under the economic
threshold level. Losses induced by nematodes de-
pend on the nematode species, the type of dam-
age induced, and the final destination of the
potato crop (seed, fresh market, or processing).
Plant parasitic nematodes also may contribute to
disease complexes that result in synergistic inter-
actions with other pests or pathogens, including
the loss of resistance to other diseases, as found
with
Globodera
-
Verticillium dahliae
and
Pratylen-
chus
-
V. dahliae
(Back
et al
., 2002),
Meloidogyne
spp. and fungus (
Verticillium
,
Fusarium
, and
Rhizoctonia
spp.), or bacteria (
Ralstonia solan-
acearum
and
Erwinia
spp.) in warm regions (Bro-
die
et al
., 1993). Potato viruses transmitted by
stubby-root nematodes are also a major concern
in some potato growing areas. The impact of
these interactions with other pathogens is re-
lated to nematode numbers and the infective
capacity of the nematode during the crop cycle;
thus, a primary goal is controlling nematode
population levels in the field. In the UK, £9 mil-
lion is spent annually on nematicides to control
PCNs (DEFRA, 2004), and in the USA, US$20
million is spent in Washington State to control
M. chitwoodi
and
M. hapla
(Santo, 1994). Crop-
ping history, nematode soil analysis (identifica-
tion and quantification), experience with local
soils, and crop benefit are all important factors
to consider in making nematode management
decisions. Reliable identification based on an in-
tegrative view of classical and molecular tech-
niques is decisive in planning strategies, as are
crop rotation or the use of resistant cultivars.
potato cyst, stem and root-lesion nematodes and
other endoparasites or semi-endoparasites can
be introduced into the field by seed potatoes;
therefore, the use of certified potato seed is es-
sential to avoid new introductions. Special
attention is required to identify symptomless seed
potatoes that are infected with
M. javanica
and/
or
M. chitwoodi
or
M. hapla
in the cooler areas of
production because of the shorter growing sea-
sons (Santo, 1994). Also, viruses such as TRV
can be spread by symptomless potato clones, and
different virus-nematode vector combinations
show specific interactions with cultivars (Xeno-
phontos
et al
., 1998). For this reason, sensitive
techniques like RT-PCR are the most appropriate
test in seed certification against TRV.
Agronomical measurements
Crop rotation
Crop rotation can be useful, depending on the
nematode species concerned. For the major
PPNs of potato (
Globodera
spp. and
Meloidogyne
spp.), this strategy is less effective, and long
rotation periods must be used due to the long
survival of dormant eggs within the cysts of
G. pallida
and
G. rostochiensis
, or because of the
wide host ranges for
Meloidogyne
spp. The aver-
age decline rates for PCNs are approximately
20-
30% per year in UK conditions (Clayton
et al
.,
2008), and a
7-
year rotation between potato
crops is a typical recommendation (EPPO,
http://
bodera_pallida/HETDSP_ds.pdf
)
. However, the
rate of decline is different for each of the PCN
species, with
G. pallida
decline rates being par-
ticularly prolonged. Decline is also affected by
the susceptibility/tolerance of the variety, and
by environmental factors such as soil type
(Hockland, 2010). Crop rotation can be com-
bined with nematicide application and/or the
use of resistant potato varieties in order to main-
tain the population at manageable levels over a
shorter rotation period. Amendments such as
poultry litter compost (in the case of
P. penetrans
)
are also reported to increase the efficacy of these
measures (Everts
et al
., 2006). However, com-
mercially attractive cultivars with full resistance
are not always available, as in the case of
G. pallida
,
and both crop rotation and granular nematicides
Management strategies
Prevention of spread
Prevention of spread is one the most important
strategies for PPN management, because once a
field is infested, complete nematode eradication
is difficult to achieve and may incur significant
short- and long-term costs. Nematodes move
short distances in the soil, so spread from in-
fested to non-infested areas is associated mainly
with human activities such as the movement of
contaminated soil attached to farm equipment,
boots, and the hooves of animals, infected plant
material including farm-saved seed, and in re-
used irrigation water (Santo, 1994). Root-knot,
