Geocenamus brevidens (Allen, 1955)
Synonyms: Tylenchorhynchus brevidens Allen, 1955
Geocenamus brevidens Brzeski
Female: Body straight to ventrally arcuate, length 0.54-0.69 mm.
about 1.1 µm wide near middle, lacking longitudinal striations.
with 6 smooth incisures, about one-third as wide as body, not
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 µm behind spear
Median esophageal bulb well developed, oval, with distinct refractive
valve in center.
Esophageal base not extending over intestine; esophago-intestinal valve
Vulva a transverse slit, about one-third body-width long.
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
Tail sub-cylindrical, finely annulated, with unstriated, round to
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.
slightly cephalated and ventrally arcuate, with distinctly notched distal ends.
Gubernaculum in ventral
view disc-like, 4.5 µm wide, not protrusible.
Reported median body size for this species (Length mm; width micrometers; weight micrograms) - Click:
U.S., Australia, Europe, and South America.
in California Nematode Pest Rating System.
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.
Grasses, cereals, garlic, alfalfa, potato, peas, pears - Alfalfa in the
Davis area and elsewhere in Northern California.
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
Wet soils shorten survival of M. brevidens; nematode can survive for 1
month in wet soil; 9 months in dry.
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).
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).
Host Plant Resistance, Non-hosts
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