|Sugarbeet Cyst Nematode||Classification||Hosts|
|Morphology and Anatomy||Life Cycle|
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Heterodera schachtii Schmidt, 1871
Sugarbeet Cyst Nematode
White, flask-shaped, with short neck embedded in host
root and swollen body on root surface. Terminal vulva on
conical protruberance (`vulval cone') covered with
gelatinous matrix containing eggs.
Head small, neck expanding rapidly, then cylindrical; excretory pore at `shoulder' where body swells to nearly spherical shape terminating in vulval cone, with anus dorsally sub-terminal. Head skeleton weak.
Stylet slender with small knobs.
Median esophageal bulb prominent, spherical.
Esophageal glands overlapping intestine latero-ventrally.
Paired ovaries long and much coiled.
A few eggs are deposited in a gelatinous matrix, but most retained in body.
Cuticle basically three-layered, superficially covered with a reticulum of ridges (for detailed structure see Shepherd, Clark & Dart, 1972).
Cyst: When the female dies, the cuticle becomes tanned, brown, tough and minutely rugose, forming a protective envelope, the cyst, containing 500-600 eggs.
Cysts of H. schachtii can be distinguished from those of other species of the genus by their shape and the features of the vulval cone.
The terminal vulval slit is about as long as the `vulval bridge' which is flanked on either side by a kidney-shaped thin area of the cyst wall that breaks down in older cysts leaving 2 apertures or `semi-fenestrae' separated by the `vulval bridge.'
Within the cone are the remains of the vagina attached to the side walls by the `under-bridge' and a number of irregularly arranged, dark brown `bullae' situated a short distance below the vulval bridge. These features and the morphology of the second stage juveniles are useful for identifying cysts extracted from soil (Cooper, 1956; Mulvey, 1960; Hesling, 1965).
The surface of mature females and newly-formed cysts is encrusted with a white waxy material referred to as the `sub-crystalline layer' which soon falls off the cyst when it is loose in the soil. The layer has been investigated in some species of the genus and is probably formed from fatty acids produced by a fungus living symbiotically on products excreted by the female nematode when feeding (Brown et al., 1971).
Body annules 1.4 µm wide in spear region and 1.7 µm at midbody. Lateral field with 4 incisures.
Stylet moderately heavy with prominent, forwardly-directed knobs.
Esophagus as in male, but median bulb more prominent; dorsal gland duct opening 3-4 µm behind spear base.
Anus obscure, about 4 anal body-widths from terminus. Tail acutely conical with rounded tip; a distinct hyaline terminal section 1-1.25 times the stylet length.
Genital primordium with 2 nuclei, located slightly behind mid-body. Phasmids obscure, just post-anal.
Fourth stage juvenile metamorphosis to male (lower left), adult malre (H), and infective second-stage juvenile (L)
usually straight with posterior quarter spirally twisted
through 90-180 degrees when heat relaxed; tapering
gradually anteriorly until, at neck, it is about half the
mid-body width. Terminus bluntly rounded with tail less
than half body-width long; phasmids
Head offset, dome-shaped, with 3 or 4 annules (Allen, 1952) and hexaradiate skeleton with lateral sectors slightly narrower than sub-laterals; small slit-like amphid apertures in lateral sectors close to oral opening. Anterior cephalids at second, posterior at sixth to eighth annule behind head constriction.
Stylet well developed with knobs concave anteriorly.
Esophageal glands overlying intestine ventro-laterally, the dorsal gland duct joining the espohageal lumen about 2 µm behind spear base, the 2 sub-ventrals opening into median bulb lumen close behind valve.
Testis single, blunt-ended.
Egg hatch: Heterodera schachtii
Distributed throughout Europe from Spain to Finland and Eire to Bulgaria. Also recorded in Soviet Union, Turkey, Israel; in U.S. in both eastern and western states; in Canada, Australia, and South Africa.
C-rated pests in California.
Feeding site establishment and development typical of the genus.
Chenopodiaceae, especially Beta vulgaris. Cruciferae, all varieties of Brassica oleracea, including cabbage, cauliflower, brussels sprouts, and cruciferous weeds.
For an extensive list of host plant species and their susceptibility, copy the name
select Nemabase and paste the name in the Genus and species box
A few eggs are deposited externally in a gelatinous matrix, but most are retained in the female body.
When the female dies, the cuticle becomes a tanned, brown, tough protective envelope, the cyst, containing the eggs. The cysts become detached from the host root and remain in the soil, the contained eggs (often numbering 500 to 600) remaining viable for at least 6 years (Thorne, 1923).
In the cysts, the eggs become embryonated at the first stage juveniles molt to the second, infective stage. These individuals may remain dormant in the eggs for several years, but some hatch every year and emerge from the cysts into the soil.
Optimum temperature for hatching is 25 C, and for subsequent movement in the soil, 15 C. Optimum soil moisture is intermediate between saturated and dry (Wallace, 1963).
Hatching is stimulated by exudates from roots of host and some non-host plants, but also takes place to a lesser extent in the absence of plants.
The J2 are attracted to plant roots, enter behind the root tips and take up a feeding position close to the stele. If the plant is a suitable host, it forms syncytia on which the nematode feeds and develops to maturity.
The optimum temperature for growth and reproduction is 21-27 C, and development takes about 17 days. The fourth stage female swells greatly, rupturing the root tissues, but remaining fixed at the head; it molts and becomes flask-shaped and white, and at this stage, the subcrystalline layer begins to form.
Males are attracted to the females (Green, 1966), fertilize them, and the females then produce from the vulva the gelatinous material into which some of their eggs are laid.
When feeding finishes, the females die, the cuticle becomes tanned and protects the eggs inside from desiccation.
The eggs develop, and infective second-stage juveniles hatch 5 weeks after the roots were first invaded, and can start a second generation if suitable host roots are available.
One to 2 generations can be produced per year in temperate regions; up to 5 generations per year in Imperial Valley (California) sugarbeet fields (heat-unit dependent - Thomason and Fife, 1962). [Ref: CIH Descriptions of Plant-parasitic Nematodes, Set 1, No. 1 (1972) and H. Ferris]
Second-stage juvenile (J2) enters lateral roots which may cease to grow or die and are replaced by others resulting in a whiskered appearance.
Plants wilt, top growth and yields are reduced, initially in patches which spread with repeated crops.
Interactions occur - Rhizoctonia solani is more pathogenic to sugarbeets in the presence of H. schachtii due to rupture of root cortex providing ingress and syncytia constituting favorable sites for infection.
Crop Rotation: Six-year crop rotation in Europe - some nematodes survive the first year of rotation, but population decreases each year over the next 5 years. Legumes, especially alfalfa, aid reduction in populations in rotations (Steele & Price, 1965).
The University of California. has recommended that beets be planted every 4 to 6 years, with no crucifers planted in the rotation.
Historically, fields were monitored by sugar companies (Holly Sugar) in the Imperial Valley. In a non-infested field, beets may not be grown for more than two years in succession.
|Avoid spreading through field by equipment. Photograph
taken after land-leveling operations in a sugarbeet field in Imperial
Source: I.J. Thomason
Nematicides: 1,3-Dichloropropene (1,3-D) applied at rate of 20 gal/acre [overall treatment at 10-12 gal/acre-row (U.C.) is effective]. Temik applied at 30 lb/acre has been used with success in England.
Host-Plant Resistance: There are sources of resistance in Beta procumbens and B. patellaris, but problems of genetic compatability and chromosome number. However, resistant cultivars are under development at the USDA Research Station in Salinas (Bob Lewellyn, Plant Breeder). Resistant sugarbeets have been produced by transgenic methods in Europe (Wegelin, 2002).
For a list of plant species or cultivars (if any) reported to be immune or to have some level of resistance to this nematode species, copy the name
select Nemabase Resistance Search and paste the name in the Genus and species box
[Ref: CIH Descriptions of Plant-parasitic Nematodes, Set 1, No. 1 (1972)]
Wegelin, Tanja. 2002. Bestimmung von Funktion und Wirkungsweise des Hs1pro-1 Nematodenresistenzgens aus Beta procumbens. Schriftenreihe des Instituts für Pflanzenbau und Pflanzenzüchtung, Christian-Albrechts-Universität zu Kiel,1435-2613 ;26