Paratrichodorus minor




Rev 10/26/2021

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             Paratrichodorus minor This is a synonym for Nanidorus minor (Colbran, 1956) Siddiqi, 1974)

Stubby Root Nematode

Synonyms: Name evolved from Trichodorus christiei to Paratrichodorus christiei to Paratrichodorus Nanidorus minor to Nanidorus minor (Rafael Rodriguez) to Paratrichodorus minor.

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Morphology and Anatomy:

Nematode is 0.46 - 0.71 mm long.

Body configuration usually rounded at both ends.

Cuticle tends to swell in water and fixative when nematodes are killed.

Curved onchiostyle with dorsal groove.

Females: Diovarial.


Males: Males are rare. Caudal alae present. Single testis.

Ref. Decraemer, W. 1995

P. minor moving to root tip feeding site.

Reported median body size for this species (Length mm; width micrometers; weight micrograms) - Click:

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Widely distributed in temperate to sub-tropical climates and is most prevalent and injurious in coarse-textured soils.

Widespread in U.S. on many hosts; Christie reports nematode inhabits Muck soils in Florida.

The species is common in warmer California vineyards even in the absence of weeds or other vegetation. 

Rare in Europe.

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Economic Importance:

D-rated pest in California Nematode Pest Rating System.

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First characterized by Christie and Perry (1951) as a migratory ectoparasite that feeds over the whole of the root surface, but usually close to the root tip, including the root cap, the meristematic region, and the region of elongation.

Nematode pierces epidermal cell walls and root hairs with rapid thrusts (10 per second).


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Wide host range including alfalfa, azalea, boysenberry, vegetables, corn, tomato, onion, wheat, sugarcane, rice, grasses, etc.

For an extensive host range list for this species, click


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Life Cycle:

Ecophysiological Parameters:

For Ecophysiological Parameters for this species, click If species level data are not available, click for genus level parameters


Life cycle complete in 16-17 days at 86 F, 21-22 days at 72 F.

Temperature range: 68-95 F.

The life cycle of stubby-root nematodes is not well studied. Eggs of Paratrichodorus minor, hatch 53.3 ± 7.3 degree-days using a basal threshold of 10º C (DD10C) after egg deposition. Second stage population peaks occurred at 28 DD10C , third stage at 67 DD10C , fourth stage at 109 DD10C and adults at 143 DD10C for adults. Population densities increased in the presence of a suitable host but declined to 33% of the initial level after 300 DD10C in the absence of a host (Schneider and Ferris, 1987).

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Vectors California and Wisconsin isolates of Tobacco Rattle Virus.

Injurious to tomato and onion in the southeastern U.S.

Devitalizes root tips and stops root growth. Produces "coarse root" or "stubby root" symptoms. Injury caused by P. minor is deceptive because it often lacks discoloration, necrotic lesions, and other conditions usually associated with a disease, but there are few types of root injury that will affect the growth of a plant more quickly than devitalized root tips.

Paratrichodorus minor damage to corn

P. minor on St. Augustine grass: Nematode is a serious pathogen and economically important pest of St. Augustine grass (Stenotaphrum secundatum) in Florida and Georgia [Rhoades, H. 1962. Plant Disease Reporter 46:424-427; Heald, C.M. and V. G. Perry. 1969. Agronomy:358-369].

P. minor on sugarcane: Apt and Koike (1962a, 1962b) and Jensen et al. (1959) demonstrated the pathogenicity of this nematode to sugarcane. It caused severe stunting and prevented development of fine feeder roots of seedling sugarcane grown in pots. The tap root growth decreased in direct proportion to the number of nematodes present.

P. minor on cotton: Alhassan, S.A. and Hollis, J.P. (1966) (Phytopathology 56:573-574) Studied the effect of inoculum with 0, 100, 400, or 1600 nemas/pot in steamed soil on cotton plants (3 weeks old). Root tips were attacked, causing an overall reduction in size of root syustem. Top growth was stunted but no root necrosis was observed. Seedling weight was inversely related to both initial and final nematode density. At 1600 nematodes/plant, root systems were significantly reduced in weight, volume, area, and number of branch roots when compared to controls. High initial population gave slow increase -- low initial population (Pr) gave high final population (Pf). Around 80 P. minor/500 cc soil may cause measurable damage to young cotton seedlings in the field.

According to Sasser,: "Absence of necrosis suggests that the relationship of P. minor to the host is one of balanced parasitism."

Virus Vectoring:

Corky ringspot is caused by tobacco rattle virus (a Tobravirus), which is vectored by stubby-root nematodes (Paratrichodorus spp. and Trichodorus spp.). The condition is sometimes referred to as Spraing, a Scottish word meaning a bright streak or stripe (de Bokx, 1972).


Corky ringspot symptoms vary depending on virus strain, potato cultivar, and time of infection. Symptoms often include of brown necrotic rings, arcs, and diffuse spots which are considered quality defects and may result in after-harvest devaluation or rejection of either table or  processed potatoes.


External Symptoms of Corky Ringspot Virus on a Potato Tuber Internal Symptoms of Corky Ringspot Virus in a Potato Tuber


Corky ringspot symptoms in potato include necrotic rings and pits on the tuber surface and range from diffuse brown spots to concentric rings or arcs of brown, necrotic tissue to dark-brown necrotic tissue which extends through tuber flesh (Mojtahedi et al., 2001). The virus is usually detectable when symptoms are seen but may also be present in asymptomatic tissue (Charlton, 2006).


Tubers from soil with a history of tobacco rattle virus serve as a reservoir. The virus may spread to daughter tubers when infected tubers are used as seed (Crosslin et al., 1999). Newly formed potato tubers are quite vulnerable to tobacco rattle virus infection and tubers as small as 3-cm in diameter had corky ringspot blemishes in tobacco-rattle infested fields in Florida (Weingartner et al. (1975).


Tobacco Rattle Virus is reported in many areas of the world and more than 400 plant species in 50 plant families are susceptible to infection (Brunt et al., 1996; Dallwitz, 1980; Dallwitz et al., 1993; Hooker, 1981; Ploeg et al., 1989).


Several species of  Trichodorus and Paratrichodorus transmit M-type isolates of Tobacco Rattle Virus (Harrison and Robinson, 1986). Stubby-root nematodes are migratory ectoparasites that are mobile during each stage of their life cycle (Stark and Love, 2003) and feed primarily on meristematic cells or root tips which hinders root elongation (Crow, 2005). Damaged root tips may swell and lateral roots may emerge behind them, resulting in root proliferation.


See section on Nematode Transmission of Plant Viruses



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Nematicides are effective but not economical on many of the hosts.  Stubby root nematode is sensitive to applications of nitrogenous fertilizers, manures, certain plant extracts, and to soil fumigation, but notably quick to return to a steady base population level that almost never exceeds 80 to 100/250 cm3 soil (McKenry, unpublished data).


Host Plant Resistance, Non-hosts and Crop Rotation alternatives:

For plants reported to have some level of resistance to this species, click


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Charlton, B.A. 2006. Effects of oxamyl on suppression of the Tobacco rattle virus vector Paratrichodorus allius and corky ringspot disease of potato in the Klamath Basin of south-central Oregon.  MS Agronomy.

Charlton, B.A. 2006. Effects of oxamyl on suppression of the Tobacco rattle virus vector Paratrichodorus allius and corky ringspot disease of potato in the Klamath Basin of south-central Oregon.  MS Agronomy Thesis,  Oregon State University

Crosslin, J.M., P.E. Thomas, and C.R. Brown. 1999. Distribution of tobacco rattle virus in tubers of resistant and susceptible potatoes and systemic movement of virus into daughter plants. American Journal of Potato Research 76:191-197.

Crow, W.T. 2005. Diagnosis of Trichodorus obtusus and Paratrichodorus minor on turfgrasses in the Southeastern United States. Online. Plant Health Progress doi:10.1094/PHP-2005-0121-01-DG.

Dale, M.F.B, D.J. Robinson, and D. Todd. 2004. Effects of systemic infections with Tobacco rattle virus on agronomic and quality traits of a range of potato cultivars. Plant Pathology 53:788-793.

de Bokx, J.A. (Ed.). 1972. Viruses of potatoes and seed-potato production. Centre for Agricultural Publishing and Documentation, Wageningen.

Decraemer, W. 1995. The Family Trichodoridae: Stubby root and virus vector nematodes. Kluwer Academic Publ., Boston, MA. 360 pp.

Decraemer, W. 2011. Virus vector families Part II. Trichdoridae.Academia Press, Gent.123p.

Harrison, B.D., and D.J. Robinson. 1986. Tobraviruses. Pages 339-369 In: The Plant Viruses Vol. 2: The Rod-shaped Plant Viruses. M.H.V. van Regenmortel, and H. Fraenkel-Conrat, eds. Plenum Press, N.Y.

Jensen, H.J., and T.C. Allen. 1964. Trichodorus allius, a potential nematode vector of TRV. Phytopathology 54:1434.

Mojtahedi, H., G.S Santo, J.M. Crosslin, C.R. Brown, and P.E. Thomas. 2000. Corky ringspot disease: Review of the current situation. Proc. 39th Annual Washington State Potato Conference. Moses Lake, WA.

Mojtahedi, H., R.A. Boydston, P.E. Thomas, J.M Crosslin, and R.A. Boydston. 2002. Eliminating tobacco rattle virus from viruliferous Paratrichodorus allius and establishing a new virus-vector combination. Journal of Nematology 34:66-69.

Schneider, S.M., and H. Ferris. 1987. Stage-specific population development and fecundity of Paratrichodorus minor. Journal of Nematology 19:267-394.

Stevenson, W.R., R. Loria, G.D. Franc, D.P. Weingartner (Eds.) 2001. Compendium of Potato Diseases 2nd Edition. American Phytopathological Society, St. Paul MN 106 pp. Weingartner, D.P., J.R. Shumaker, and G.C. Smart, Jr. 1975. Incidence of corky ringspot disease on potato as affected by different fumigation rates, cultivars, and harvest dates. Proceedings/Soil and Crop Science Society of Florida 34:194-196.

Taylor C. E. and Robertson, W. M. (1975). Acquisition, retention and transmission of viruses by nematodes. Pp 253-276 in Nematode Vectors of Plant Viruses (F. Lamberti, C. E. Taylor and J. W. Seinhorst, Eds). Plenum Press, London. 460 p.

Weingartner, D.P., and J.R. Shumaker. 1990. Effects of soil fumigants and aldicarb on corky ringspot disease and trichodorid nematodes in potato. Supplement to the Journal of Nematology 22:775-778.

Copyright © 1999 by Howard Ferris.
Revised: October 26, 2021.