Syn.: | Trichodorus minor Colbran, 1956
Paratrichodorus (Nanidorus) minor (Colbran, 1956) Siddiqi, 1974 Nanidorus minor (Colbran, 1956) Siddiqi, 1974 Trichodorus christiei Allen, 1957 Paratrichodorus (Nanidorus) christiei (Allen, 1957) Siddiqi, 1974 |
[Note: Allen (1957a), Hooper (1962) and Siddiqi (1962c) remarked
on the similiarities between Paratrichodorus christiei and P.
minor. Siddiqi (1963) suggested that the two species could be
separated by differences in spicule length of the very rarely occurring
males and Siddiqi (1974a) suggested that the two species could be separated
on onchiostyle length. However, Loof (1975), after studying various
populations including paratypes of P. christiei, concluded that
these differences were not as marked as first supposed and formally declared
P.
christiei a junior synonym of P. minor.]
Diagnosis: (Modified from Hooper, 1977)
Female: Body almost straight when heat relaxed, short, tapering
slightly at both ends. Cephalic region rounded with slightly protruding
papillae. Onchiostyle typical for the genus. The pharyngeal
lumen, ventral to the onchiostyle, leads into the lumen of the narrow anterior
part of the oesophagus which gradually expands into a spathulate to pyriform
basal bulb overlapping the intestine ventrally and subventrally.
Narrow part of oesophagus surrounded by a nerve ring. Exretory pore
usually opposite the base of the oesophagus. Lateral body pores and
caudal pores absent. Anus subterminal and the very short tail bluntly
rounded. Genital tracts amphididelphic, reflexed; no distinct spermatheca.
Vulva a short transverse slit; vagina weakly developed, extending for only
about one-third of the body width. Refractive thickenings at the
vulva inconspicuous, almost rod-like and nearly parallel to the cuticle
in lateral view.
Male: Extremely rare. The oesophageal region of the male resembles the female described above. Testis single, outstretched. Spicules large with slight ventral curvature towards the tip, marked with fine transverse striations. Gubernaculum with a small distal keel. A single, ventromedian papilla 9 um anterior to the cloaca. A single, postanal, subventral papilla present on left side near tail terminus [specimen apparently aberrant as noted by Siddiqi (1963), in that the corresponding subventral papilla, usually found in trichodorid males, is missing from the right side.] Bursa envelopes the tail beginning at a level just anterior to the precloacal papilla.
Bionomics:
P. minor (= P. christiei) prefers sandy or sandy-loam
soils with highest populations at a depth of 30 cm (Brodie, 1976). Reproduction
is parthenogenetic or, according to Sturhan (1989), hermaphroditic.
Males are exceedingly rare. The life cycle lasts 21-22 days at 22C
and and 16-17 days at 30C (Rohed and Jenkins, 1957). The direct
feeding activities result in the typical stubby-root symptoms, the first
record of which was by Christie and Perry (1951). P. minor has been
recorded as transmitting tobacco rattle virus (TRV) in the USA and also
pepper ring spot virus (PRV) in South America. It is extremely polyphagous,
feeding on crops such as avodado, brassicas, lucerne, onion, potato, sugarbeet,
sugarcane, sweet potato, tomato, etc.
Distribution:
Mainly recorded from the tropical and subtropical regions of the world
where it is often almost ubiquitous (Africa, Asia, Central and South America,
USA). According to Rashid et al.(1986b) P. minor is
not indidenous to South and Central America, but has been introduced with
crop plants, a suggestion borne out by its distribution and host associations.
P.
minor is occasionally recorded from Europe.
(Description- Hunt, 1993)
DNA Sequences Obtained
Specimen: | Collected: |
GD868-01 | Poteet, Texas |
GD868-04 | Poteet, Texas |