Merlinius brevidens




Rev 12/27/2013

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Morphology and Anatomy Life Cycle
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Merlinius brevidens (Allen, 1955) Siddiqi, 1970


 Synonyms:      Tylenchorhynchus brevidens Allen, 1955

                        Geocenamus brevidens Brzeski

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Morphology and Anatomy:

  • Female: Body straight to ventrally arcuate, length 0.54-0.69 mm.

  • Annules about 1.1 m wide near middle, lacking longitudinal striations.  

  • Lateral fields with 6 smooth incisures, about one-third as wide as body, not areolated.  

  • Deirids present near or at level of excretory pore; latter just behind poorly developed hemizonid, situated between nerve ring and basal esophageal bulb.  

  • Lip region broadly rounded, continuous with body contour.  Lip region has 5 or 6 annules; labial framework lightly sclerotized. 

  • Stylet moderately developed; basal knobs rounded, backwardly sloping.  Orifice of dorsal esphageal gland 2 to 5 m behind spear base.  

  • Median esophageal bulb well developed, oval, with distinct refractive valve in center.  

  • Esophageal base not extending over intestine; esophago-intestinal valve (=cardia) conoid-rounded.  

  • Vulva a transverse slit, about one-third body-width long.  

  • Spermathecae rounded, well formed and with sperms only in impregnated females, which are not common in a population. 

  • Oocytes in one line except for a few in germinal zone of ovary.

  • Intestine not overlapping rectum or extending into tail cavity.  

  • Tail sub-cylindrical, finely annulated, with unstriated, round to flattened terminus.

  • Phasmids minute, usually just behind middle of tail.


  • Male: Uncommon, probably not essential for reproduction. 

  • Length, male: 0.56-0.64 mm

  • Bursa finely crenate, extending to end of tail.  

  • Hypoptygma distinct.  

  • Spicules slightly cephalated and ventrally arcuate, with distinctly notched distal ends.

  • Gubernaculum in ventral view disc-like, 4.5 m wide, not protrusible.


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U.S., Australia, Europe, and South America.

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Economic Importance:

D-rated pests in California. 


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Merlinius brevidens is an ectoparasite on root hairs and epidermal cells; average feeding time is 11 min. 

The nematodes appear to be indiscriminate in their choice of feeding sites, and move rapidly from one site to another.

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Grasses, cereals, garlic, alfalfa, potato, peas, pears - Alfalfa in the Davis area and elsewhere in Northern California.

For an extensive list of host plant species and their susceptibility, copy the name

Merlinius brevidens

select Nemabase and paste the name in the Genus and species box



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Life Cycle:

Male uncommon, probably not essential for reproduction.   

Bridge (1970) observed that a female laid 11 eggs over a period of 120 hours while feeding, and the newly hatched juveniles fed on the same root as their parent. 

Wet soils shorten survival of M. brevidens; nematode can survive for 1 month in wet soil; 9 months in dry.


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Langdon et al. (1961) found that M. brevidens was associated with stunt symptoms in wheat and barley in Oklahoma.  

Varo Alcala et al. (1970) reported that this nematode causes increased cellulose thickenings of the external cell walls of the root hypodermis of wheat and barley in Spain.

Nematode feeding may increase susceptibility of barley and wheat to invasion by Olpidium fungus (Langdon et al., 1961).

Yields of no-till annual spring wheat (Triticum aestivum) in eastern Oregon were inversely correlated with population levels of Merlinius (Geocenamus) brevidens. Soil treatment with Aldicarb improved grain yields (Smiley et al., 2006).



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Soil fumigation with ethylene dibromide (EDB) decreased the populations of M. brevidens in Californian pear orchards, but there was no evidence to indicate a correlation between the population density of the nematode and pear vigor (Lownsbery et al., 1964).


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

Merlinius brevidens

select Nemabase Resistance Search and paste the name in the Genus and species box


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CIH Descriptions of Plant-parasitic Nematodes, Set 1, No. 8 (1972)

Smiley RW, Whittaker RG, Gourlie JA, Easley SA. 2006. Geocenamus brevidens associated with reduced yield of no-till annual spring wheat in Oregon. Plant Disease 90:885-890.

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Copyright 1999 by Howard Ferris.
Revised: December 27, 2013.