Heterodera trifolii
Contents
Rev 08/31/2007
Heterodera trifolii |
Contents |
Rev 08/31/2007 |
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| Clover Cyst Nematode |
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Classification |
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Hosts |
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Morphology and Anatomy |
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Life Cycle |
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Economic Importance |
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Damage |
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Distribution |
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Management |
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Feeding |
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References |
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Tylenchida
Tylenchina
Tylenchoidea
Heteroderidae
Heteroderinae
Heterodera trifolii (Goffart, 1932)
Synonyms: Heterodera shachtii var. trifolii (Goffart, 1932)
Heterodera schachtii trifolii (Goffart, 1944)
Heterodera (Heterodera) trifolii (Skarbilovich, 1959)
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| 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. |
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. schachtii by its heavier and more strongly pigmented underbridge, with bifurcate ends, its greater fenestral length, and shorter vulva-anus distance. |
Cosmopolitan species, occurring widely throughout northern Europe and Spain, Italy, southern France, Soviet Union, Canada, U.S., Israel, India, Australia and New Zealand.
D-rated pests in California.
Feeding site establishment and development typical of genus.
Attacks legumes (86 species in 9 families). Several forms of clover are reported as hosts of H. trifolii in New Zealand (Mercer and Woodfield, 1986). A species thought to be H. trifolii is a serious pest of carnation in Italy and in glasshouses in southern France.
There may be several pathotypes of H. trifolii.
Root leachates stimulate hatching and attract juveniles to root-tips. E
ggs are produced early by the adult white female; the first eggs are laid in a gelatinous matrix adhering to the vulval cone. Most eggs, however, mature within the extensive gonad as the cyst develops, and are retained within the brown cyst.
First-stage juveniles molt to the second, infective stage within the egg. Hatching of the eggs retained within the protective cyst, however, occurs progressively over a period of years in the soil in response to moisture and root leachates. Emergence from juveniles in cysts may be seasonal and influenced by diapause and temperature. Juveniles emerge over a relatively wide range of temperatures (4.2 to 31.4 C), with 17.2 C being optimum (Oostenbrink, 1967).
Multiple infections may kill root tip.
Freckman & Chapman (1972) showed that, with mixed infestations of H. trifolii and M. hapla), syncytia and giant cells occurred side-by-side with no interference.
Methods for controlling other species of Heterodera are generally applicable for this species, although seldom employed.
Resistance is known in some white clovers (Kuiper, 1960) and soybeans (Mankau & Linford, 1956).
Endo & Schaeffer (1967) discovered that applications of the chemical azauracil consistently arrested further development of early third-stage juveniles in red clover under greenhouse conditions.
Nematicides: In France, also in greenhouses, Aldicarb applied in November and February at doses of 45, 7.5 or 19 kg a.i./ha, resulted in reduced infestation and increased flower yield in carnation nurseries (Cuany, 1970).