Male: Rarely
reported. Length = 0.97-1.29 mm; width = 30 µm. Body
robust, vermiform. Lip region set off from neck,
rounded, with 6 annules.
Stylet well-developed with knobs slightly backward
sloping.
Esophageal
glands less well-developed than in
infective second-stage juvenile.
Excretory
pore posterior to esophago-intestinal valve.
The is hemizonid
6 to 14 annules in from of the excretory
pore (Norton 1967).
Testis single; spicule
curved, blades with truncated
or oblique lips, not appearing bidentate. Gubernaculum
simple, proximity arcuate. According to Norton (1967),
the spicules appear to be bidentate.
Second-stage Juvenile: Head offset,
with 4 annules, head skeleton heavily sclerotized.
Stylet robust, anterior surfaces of knobs concave.
Dorsal gland duct opening 5-9 µm posterior to spear
knobs. Esophageal
glands, particularly the subventrals,
well-developed, extending ventrally or ventro-laterally
well posterior to esophago-intestinal valve.
Tail conoid, tapering uniformly to a finely rounded
terminus. Posterior half of tail hyaline. Phasmids
small,
usually obscure, located near middle of tail.
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White
Females: Length = 520-650 µm; width = 320-340 µm. Found on
roots. Lemon-shaped with prominent neck and vulval cone (posterior
protuberance). Median
esophageal bulb rounded, with distinct valve.
Ovaries paired, greatly extended and nearly filling
the body cavity of the adult female.
Vulval cone covered with a gelatinous matrix
containing as many as 200 eggs (Thorne, 1961).
Surface of female and newly-formed cysts typically
encrusted with a material termed "subcrystalline
layer." Transitional stage between white female and
brown cyst distinctly yellow. The yellow color varies
with the strain of the host plant, being constant in
females developing on any one host strain (Norton, 1967).
Cyst: Brown to dark brown containing
a few to several hundred eggs, eventually becoming
detached from the roots to lie in the soil where the
protected eggs may remain viable for several years.
Identification of species of Heterodera is
based largely on the cone top structures, including
fenestra (thin-walled areas around the gonopore of the
cyst), vulval slit length, underbridge and
bullae (see Mulvey, 1972).
H. trifolii can be separated from H.
trifolii by its heavier and more strongly
pigmented underbridge, with bifurcate ends, its greater
fenestral length, and shorter vulva-anus distance.
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