Agriculture Reference
In-Depth Information
Chapter 8
Nematodes Which Challenge Global
Wheat Production
Richard W. Smiley and Julie M. Nicol
SUMMARY
ylenchus
species, may occur within
individual fi elds.
(4) Field sanitation is important because these
nematodes multiply on many weed species
and volunteer cereals. Cereal cyst nematode
can be controlled by rotating wheat with a
noncereal, a resistant cultivar, or weed-free
fallow. Root-lesion nematode is best
managed by rotating resistant and tolerant
wheat cultivars with other poor hosts.
(5) Resistance and tolerance are genetically
independent, and cultivars resistant or tol-
erant to one species are not necessarily
resistant or tolerant to another species.
Root-lesion nematode resistance is quanti-
tative and cereal cyst nematode is con-
trolled by single-gene resistance. Molecular
markers have been developed to identify
genes and quantitative trait loci for resis-
tance in seedlings.
(6) Molecular tests to identify and quantify
nematodes in commercial soil testing labo-
ratories will allow more effective surveys
of populations. Greater collaboration is
needed between research institutions,
organizations, and countries.
(1) Effects of cereal cyst (
Heterodera
) and root-
lesion (
Pratylenchus
) nematodes on wheat
are diffi cult to identify and control. Symp-
toms are nonspecifi c and easily confused
with stress from nutrient defi ciency,
drought, or disease.
(2) Multiple species of
Heterodera
and
Prat-
ylenchus
are capable of damaging wheat.
Identifi cation of species is diffi cult and
procedures based on comparative mor-
phology can be unreliable. Identifi cation of
species is now assisted by molecular tools.
(3)
Heterodera
species discussed in this chapter
reproduce only on hosts within the Poaceae,
and individual species are highly heteroge-
neous for virulence to specifi c host geno-
types. Many pathotypes occur within
H.
avenae
, and the same is anticipated for
H.
fi lipjevi
and
H. latipons
. No pathotypic
variation within either
P. neglectus
or
P.
thornei
has been reported on wheat, but
both species multiply in a wide range of
monocot and dicot hosts. Mixtures of
Het-
erodera
species or pathotypes, and
Prat-
INTRODUCTION
2 mm long. They puncture cells and damage plants
mechanically and chemically, reducing plant vigor,
inducing lesions, rots, deformations, galls, or root
knots, and predisposing plants to infection by root-
infecting fungi. World crop production is thought
to be reduced 10% by damage from plant-parasitic
nematodes (Whitehead 1997).
Plant-parasitic nematodes are tiny but complex
animals (unsegmented roundworms) anatomically
differentiated for feeding, digestion, locomotion,
and reproduction (Barker et al., 1998). Most species
are transparent, vermiform (eel-shaped), and 0.5-
