Figure 1. Soybean field
with symptoms of infection by soybean cyst nematode, Heterodera
glycines. Note poor stand and stunting of soybean plants.
(Printed with permission of Dr. Lorin R. Krusberg, Department
of Botany, University of Maryland, College Park, MD).
Figure 2. Segment of
soybean root infected with soybean cyst nematode. Signs of infection
are brown-white females or cysts with egg masses that are attached
to root surfaces.
Figure 3. Histological
section of soybean root showing intracortical penetration by an
infective juvenile of soybean cyst nematode at 1 day after inoculation.
Figure 4. Longitudinal
section of soybean root showing a third-stage juvenile of soybean
cyst nematode at its feeding site and a syncytium. The syncytium,
which functions as a food reservoir, has dense cytoplasm and multiple
nuclei that result from dissolution of cell walls.
Figure 5. Extensive syncytium
induced by a third-stage juvenile of soybean cyst nematode at
10 days after inoculation. Note cell wall fragments dispersed
Figure 6. Cross section
of soybean root resistant to soybean cyst nematode, showing restricted
development of nematodes and associated syncytia at 5 days after
Figure 7. Cross section
of root from a susceptible soybean cultivar, showing extensive
sectors of xylem and phloem tissues replaced by syncytia with
dense cytoplasm. At 21 days after inoculation, a nematode at this
site (not shown) would be an adult female producing eggs that
are either embedded in a gelatinous matrix secreted by the nematode
or held within the cyst body for long-term survival and subsequent
dispersal (see fig 2.)
Figure 8. Cross section
of susceptible soybean cultivar at 40 days after inoculation,
showing sectors of root occupied by syncytia. Some syncytia have
been replaced by parenchymatous tissue.
Figure 9. Cross section
of resistant soybean cultivar at 31 days after inoculation, showing
minimal damage to vascular system. Necrotic area indicates former
site of syncytium induced by nematode.
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