Rev 09/12/2023
Dolichodorus heterocephalus Cobb, 1914
Type species of the genus
Synonyms: None.
The genus Dolichodorus was erected by Cobb ( 1914) when he named D. heterocephalus from fresh water at Silver Springs, Florida and Douglas Lake, Michigan.
Length, female: 2.1-2.7 mm; length, male: 1.7-2.2 mm.
Female:
Head somewhat flattened dorso-ventrally, with four prominent lobes (2 subdorsal, 2 subventral) which have a continuous outline in face view and are not separated from each other by deep clefts as in, for example, Belonolaimus longicaudatus. In lateral view, head rounded, set off from body by deep constriction and with nine or more faint transverse lines corresponding to the eight or more minute head annules. When specimens are not quite lateral, the head appears wider due to its dorso-ventral flattening.
Long stylet with cone longer than shaft. Stylet flexible, bends with body. Has strong backward sloping knobs 6.5-7.5 µm across.
Esophageal lumen folded in procorpus when stylet retracted.
Median bulb well-developed.
Basal esophageal bulb elongate-pyriform, butting with intestine, with 3 nuclei, one larger dorsal nucleus situated about half-way along bulb, and 2 smaller subventral nuclei at the same level or posterior to it.
Excretory pore variable in position, 75-130 annules behind head; at its most forward position opposite the anterior half of the median bulb, but more generally opposite the posterior half of the bulb to the level of the nerve ring.
Hemizonid usually 4 annules long, 14-44 (28 av.) annules behind excretory pore.
Vulva a transverse slit with a pair of opposing sclerotized pieces in lateral view.
Ovaries paired, outstretched, spermathecae present.
Intestine extending beyond rectum to form a sac.
Anterior part of tail rounded or conoid merging into the conoid spike of the posterior part. Paracer et al. (1968) noted that females of D. heterocephalus with bluntly rounded tails appeared occasionally in a Massachusetts population.
Lateral field with 3 incisures, completely areolated. Anteriorly, the middle line first appears a few annules behind the head, the outer lines arising some annules further back. Posteriorly, the outer lines disappear, leaving the central incisure on the tail.
Phasmid inconspicuous situated on the central line posterior to anus.
[Ref: CIH Descriptions of Plant-parasitic Nematodes, Set 4, No. 56 (1974)]
Male:
Similar to female, except for sexual dimorphism.
Spicules slightly arcuate, distal end of gubernaculum with small reflexed process, tip protruding from body.
Males have unique caudal alae, well-developed, finely crenate, and trilobed; tail terminus with small notch, seen in dorsal or ventral view.
Egg:
Smart et al. (1973) describe the presence of an outer uterine layer or protein coat on the egg, thought to be the first report of such a layer on the egg of a plant-parasitic nematode.
Reported median body size for this species (Length mm; width micrometers; weight micrograms) - Click:
Eastern U.S., especially Florida (wet areas); also in virgin soil in South Africa. In Zimbabwe, I encountered Dolichodorus on roots of a Julbernardia tree at 7 ft. below soil surface near water table, although the species was not confirmed).
Cranberry bogs in Massachussetts.
Related genus Neodolichodorus occurs in wet areas of Napa Valley and Coastal range of California, for example a citrus tree near a well in Yountville, on a bay tree next to a stream near Lake Berryessa.
A-rated pest in California Nematode Pest Rating System.
Ectoparasite mainly at root tip; nematode has long stylet.
During feeding of D. heterocephalus, Paracer et al. (1967) observed discrete root galls, curvature at the root tips and localized lesions in the root cortex and epidermis. There was some enlargement of nuclei in cortical cells at the feeding site.
The root damage leads to plant stunting and other effects of debilitatd roots.
Celery, sweet corn, water chestnut, bean, tomato, pepper, cranberry, cabbage, balsam, and carnation.
Ecophysiological Parameters:
Nematode prefers wet locations with high soil moisture.
Field infestations in Florida may be due to soil spreading from riverbanks onto fields and into irrigation water (Christie, 1959).
Males and females are both present.
Life history parameters not well known. Paracer et al. (1968) gives some information on the biology of Massachusetts populations: the first larval molt occurs in the egg; second stage juveniles hatch after 14-17 days at 20-23 C.
Males, females, and all larval stages feed, individuals sometimes remaining at one location on the root for up to 7 days.
The nematode does not survive in fallowed pots for longer than 3 months.
Several different biotypes of D. heterocephalus may be present (Florida and Massachusetts populations) (Paracer et al., 1968); they are distinguished by the host status of celery to them.
Feeding causes brownish cortical lesions and enlarged cortical nuclei; root elongation ceases; secondary roots are attacked, resulting in stubby-root symptoms; some terminal galling may be observed.
Perry (1953) observed severe stunting, accompanied by depleted root systems of celery and corn, in field infestations of D. heterocephalus in Florida. Celery yield was reduced by 50% in one field.
Water chestnut growing in hydroponic beds was also stunted; nematode feeding also causes stunting of tomato, bean, and pepper (Perry, 1953).
Damage is reported on a range of plants, including celery, garden balsam and sweet corn, in moist sandy soils (Christie, 1952; Tarjan et al., 1952; Perry, 1953; Paracer et al., 1967).
Use of nematicides, such as 1,3-Dichloropropene (Telone) or, earlier, ethylene dibromide (EDB).
Drying of moist soil areas gives effective control.
[Would dry fallow for at least 3 months also be effective under field conditions?]
Host Plant Resistance, Non-hosts and Crop Rotation alternatives:
Christie, J.R. 1952. Some new nematodes of critical importance to Florida growers. Proceedings - Soil Science Society of Florida 12:30-39.
CIH Descriptions of Plant-parasitic Nematodes, Set 4, No. 56 (1974)
Cobb, N.A. 1914. The North American free-living fresh-water nematodes. Transactions of the American Microscopical Society, 33: 69-133.
Paracer, S.M. and B.M. Zuckerman. 1967. Monoxenic culturing of Dolichodorus heterocephalus on corn root callus. Nematologica 13:478.
Paracer, S.M., M. Waseem and B.M. Zuckerman. 1967. The biology and pathogenicity of the awl nematode, Dolichodorus heterocephalus. Nematologica 13:517-524.
Perry V.G. 1953. The awl nematode, Dolichodorus heterocephalus, a devastating plant parasite. Proceedings of the Helminthological Society of Washington 20:21-27.
Scheck, H. 2021, California Pest Rating Proposal for Dolichodorus heterocephalus Cobb, 1914. CDFA website.
Tarjan, A.C., B.F. Lownsbery and W. D. Hawley. 1952. Pathogenicity of some plant-parasitic nematodes from Florida soils. I. The effect of Dolichodorus heterocephalus Cobb on celery. Phytopathology 42:131-132.