Agriculture Reference
In-Depth Information
and wheat (Eastwood et al., 1994; Williams et al.,
1994, 2006; Kretschmer et al., 1997; Barr et al.,
1998; Paull et al., 1998; Eagles et al., 2001; Ogbon-
naya et al., 2001a,b; Martin et al., 2004; Barloy et
al., 2007). Some of these markers have been used
in marker-assisted selection and for pyramiding
genes for resistance.
Practices other than crop rotation and planting
resistant cultivars are less effi cient; however,
components of these strategies could still form
part of an integrated pest management approach
to nematode control. Other cultural methods
(Nicol and Rivoal 2007) include manipulating the
sowing time to minimize the impact of the major
hatching period, as when winter wheat is planted
during autumn in cool, temperate regions where
the major hatch occurs during spring.
Heterodera
avenae
populations can also be reduced by plant-
ing a susceptible host as a trap crop prior to the
major hatching period, thereby encouraging a
maximum hatching effi ciency by a plant stand
that is then killed before new cysts are developed.
The greatest crop loss occurs when nutrients or
water become limiting for maximum plant growth
potential at any point during the growing season.
Crop damage is therefore minimized by supply-
ing optimal plant nutrition (Color Plate 16) and,
where possible, supplemental water during inter-
vals of drought.
Biological control products are not commer-
cially available, but
H. avenae
populations in some
locations are maintained below an economic
threshold by fungal and bacterial parasites of eggs
and juveniles (Kerry 1987; Kerry and Crump
1998; Ismail et al., 2001).
A low rate of nematicide application can provide
effective and economical control of cereal cyst
nematode in wheat (Brown 1987). However,
current environmental concerns associated with
these chemicals eliminate them as a viable alterna-
tive for use by farmers. They will, however, con-
tinue to be an important research tool for studying
yield loss and population dynamics.
Once introduced into a region or country it
is very diffi cult to minimize the spread of cyst
nematodes. They are effi ciently disseminated
by all means of soil movement, including
minute amounts of soil that contaminate equip-
ment, by animals and plant products, and by
soil that is moved by water and wind. Rapid
dissemination together with increased reporting
of
H. avenae
is especially well illustrated in
China, where this nematode was fi rst reported
in 1987 and is now reported in at least eight
provinces (Nicol and Rivoal 2007; Peng et al.,
2007). Likewise,
H. avenae
was fi rst reported
in the western US in 1974 and is now reported
in at least seven states (Smiley et al., 1994,
2005c).
ROOT-LESION NEMATODE
At least eight species in the genus
Pratylenchus
are
parasitic to wheat (De Waele and Elsen 2002;
Nicol 2002; Nicol et al., 2003; McDonald and
Nicol 2005; Castillo and Vovlas 2007). Four
species (
P. crenatus
,
P. neglectus
,
P. penetrans
, and
P. thornei
) occur throughout the world in temper-
ate cereal-producing regions.
Pratylenchus neglectus
and
P. thornei
are the
species most often associated with yield loss in
wheat and are emphasized in this chapter. One or
both species occur in Australia, Europe, the
Indian Subcontinent, the Mediterranean Basin,
the Middle East, West Asia, North Africa, and
North America (Nicol and Rivoal 2007).
Prat-
ylenchus thornei
is considered the most economi-
cally important species on wheat and has reduced
yields as much as 85% in Australia, 37% in
Mexico, 70% in Israel, and 50% in the US (Arm-
strong et al., 1993; Nicol and Ortiz-Monasterio
2004; Smiley et al., 2005a).
Pratylenchus neglectus
also causes losses up to 37% in the US (Smiley
et al., 2005b).
Symptoms and epidemiology
Pratylenchus
species are migratory root endopara-
sites capable of multiplying in a wide range of
monocot and dicot host species (Loof 1978;
Vanstone and Russ 2001a,b; Vanstone et al.,
2008). They live freely in soil and may become
entirely embedded in root tissue but never lose
