🪱 Other Important Plant Parasitic Nematodes

In the previous lessons, we covered the major nematode groups in detail -- root-knot, cyst, seed-gall, citrus, aphelenchid, burrowing, reniform, and Ditylenchus. This final lesson provides a quick reference to twelve additional nematode genera that are frequently encountered in Indian agricultural soils and commonly tested in exams.

A coffee planter in South India dealing with lesion nematodes, a rice farmer in eastern India battling the rice root nematode, or a grape grower whose vines are declining due to the dagger nematode -- each faces a distinct challenge. This lesson covers their common names, key identifying features, and agricultural significance.

This lesson covers:

1. Migratory endoparasites -- lesion, rice root, false root-knot
2. Semi-endoparasites -- spiral, lance
3. Ectoparasites -- stunt, ring, sheath, pin
4. Virus vectors -- dagger, needle, stubby-root

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Root Lesion Nematode -- Pratylenchus sp.

Feature	Details
Etymology	Pra + Tylenchus -- first three letters from species pratensis (meadow) + genus name
Common names	Lesion nematode (from dark necrotic root lesions) and Meadow nematode (first found in grasslands, Netherlands)
Parasitism	Migratory endoparasite -- feeds in root cortex, continuously moving and creating lesions
Key Indian species	Pratylenchus coffeae -- serious pest of coffee in South India
Ranking	One of the top 3 most important nematode genera worldwide (with Meloidogyne and Heterodera/Globodera)
All stages	Found in root or soil (unlike sedentary nematodes confined to roots)

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Rice Root Nematode -- Hirschmanniella sp.

Feature	Details
Named after	Dr. Hedwig Hirschmann (eminent US nematologist)
Adaptation	Uniquely adapted to waterlogged, flooded rice fields
Disease	Mentek/Omomentek disease of rice (named in Southeast Asia)
Symptoms	Root discolouration, partially hollow roots; stunted growth in patches with reduced tillering
Damage mechanism	Migratory endoparasite consuming internal cortical tissue, leaving empty cavities

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False Root-Knot Nematode -- Nacobbus sp.

Feature	Details
Why "false"?	Produces galls resembling true root-knot (Meloidogyne) galls through hypertrophy
Key difference	Galls are indistinguishable in the field -- accurate identification requires laboratory examination of the nematode

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Spiral Nematode -- Helicotylenchus sp.

Feature	Details
Etymology	Helix (coil) + Tylenchus
Identifying feature	Body naturally coils into a tight spiral when killed -- the defining morphological character

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Lance Nematode -- Hoplolaimus sp.

Feature	Details
Etymology	Hoplo (arming) + laimos (throat)
Common name origin	"Lance" refers to its robust, heavily sclerotised stylet resembling a lance/spear
Capability	Strong stylet can penetrate even thick-walled cortical cells

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Stunt Nematode -- Tylenchorhynchus sp.

Feature	Details
Etymology	Tylos (knob) + enchos (spear) + rhynchos (snout) = knobbed spear with a snout
Common name origin	Causes pronounced growth reduction (stunting) in infected plants, particularly tobacco

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Ring Nematode -- Criconema sp.

Feature	Details
Identifying feature	Large, prominent ring-like annulations covering the body surface
Distinction	Rings are much more pronounced than fine annulations on other nematodes

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Sheath Nematode -- Hemicycliophora sp.

Feature	Details
Etymology	Hemi (half) + cyclio (rounded) + phora (bearing)
Common name origin	Females and juveniles have a loose outer cuticle (sheath) -- the retained cuticle from a previous moult
Other feature	Sickle-shaped spicules in males

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Pin Nematode -- Paratylenchus sp.

Feature	Details
Size	Smallest plant parasitic nematode (< 0.5 mm)
Feeding type	Ectoparasitic
Note	Despite tiny size, can reach very high population densities and cause measurable root damage

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Dagger Nematode -- Xiphinema sp.

Feature	Details
Etymology	Xiphidion (sword) + nema
Stylet type	Odontostyle -- one of the longest among PPNs
Key species	Xiphinema index transmits Grapevine Fan Leaf Virus
Taxonomic order	Dorylaimida (all virus-vectoring nematodes belong here)

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Needle Nematode -- Longidorus sp.

Feature	Details
Etymology	Longus (long) + dorys (spear)
Size	Among the largest soil-inhabiting PPNs -- some species exceed 5 mm
Stylet	Long hypodermal needle-like stylet for deep root feeding
Virus transmission	Transmits NEPO viruses (ring spot viruses)

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Stubby-Root Nematode -- Trichodorus and Paratrichodorus sp.

Feature	Details
Common name origin	Infected roots become abnormally short, thickened, and blunt-tipped ("stubby")
Damage mechanism	Feeds on and destroys the root meristem (growing point), stopping root elongation
Parasitism	Ectoparasites feeding on root tips
Virus transmission	Vectors of NETU (Tobacco Rattle) viruses

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Master Comparison Table

Nematode	Common Name	Parasitism	Key Feature	Crops/Significance
Pratylenchus	Lesion / Meadow	Migratory endoparasite	Dark necrotic root lesions	Coffee (South India); Top 3 genus
Hirschmanniella	Rice root	Migratory endoparasite	Hollow roots in flooded fields	Mentek disease of rice
Nacobbus	False root-knot	Endoparasite	Galls like Meloidogyne	Lab ID needed to distinguish
Helicotylenchus	Spiral	Semi-endoparasite	Body coils in tight spiral	Wide range of crops
Hoplolaimus	Lance	Ecto/Endoparasite	Robust stylet like a lance	Various crops
Tylenchorhynchus	Stunt	Ectoparasite	Causes stunting (notably tobacco)	Tobacco and other crops
Criconema	Ring	Ectoparasite	Prominent ring-like annulations	Various crops
Hemicycliophora	Sheath	Ectoparasite	Loose outer cuticle sheath	Various crops
Paratylenchus	Pin	Ectoparasite	Smallest PPN (< 0.5 mm)	Various crops
Xiphinema	Dagger	Ectoparasite	Longest stylet; transmits NEPO viruses	Grapes (Fan Leaf Virus)
Longidorus	Needle	Ectoparasite	Largest soil PPN; needle-like stylet	Transmits NEPO viruses
Trichodorus/Paratrichodorus	Stubby-root	Ectoparasite	Destroys root tip; stubby roots	Transmits NETU viruses