|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
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.
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.
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