learn about symptoms, life stages and characteristics of citrus nematode and their control measures

1. Tylenchulus semipenetrans
Citrus nematode
Prepared by
R MOHANAPRIYA
Assisstant Professor (Plant Pathology)
JSA College of Agriculture and
Technology,
Ma. Podaiyur, Cuddalore district,
Tamilnadu

2. Nematode : Citrus nematode
(causal agent of slow decline of citrus)
 First discovered in California in 1913 by J.R. Hodges and was later
described and named by Nathan Cobb
 India – 1st reported by Siddiqi 1961, Aligarh (UP)
Systematic position
Phylum : Nematoda
Class : Secernentea
Order : Tylenchida
Suborder : Tylenchina
Super family : Criconematoidea
Family : Tylenchulidae
Sub-family : Tylenchulinae
Genus : Tylenchulus(Latin. Tylos- knob & enchos–spear)
Species : semipenetrans (semi endoparasitic)
Major hosts : Citrus (host specific)
Type of parasitism : Semi endoparasite

3. Immature female
Vermiform, small (<0.5 mm)
Head - continuous, round, sclerotization weak
Stylet – medium with round basal knob.

4. Mature female
 0.35 – 0.4 mm long, neck
elongate, irregular
 Anterior part – slender, irregular
with thin cuticle
 Posterior part – swollen with
thick cuticle and projecting tail
tapering,blunt, ventrally arcuate
 Vulva and excretory pore – very
posterior; ovary – monodelphic,
anterior, convoluted; no anus or
rectum.

5. Male
 Vermiform, short,straight and
slender
 Cephalic sclerotization
 Stylet and oesophagus reduced
 Spicule slightly curved
 No bursa
 Tail – conical, pointed.

6. Second Juvenile
 Vermiform
 Tail – long, pointed
 Excretory pore at 50-60% of body
length
 Oesophagus as in females
 Genital primordium differently
shaped in male and female
juveniles.

7. Biology & Life Cycle
• Sedentary semi endo parasite
• Second stage juveniles cause infection of the fine feeder roots
• Life cycle - 6-8 weeks (eggs hatch out – 12-14days at24o C)
• Freshly hatched female juveniles start feeding on epidermal
cells of young feeder roots.
• They penetrate the root tissues and initiate nurse cell feeding
sites deep in the cortex.
• When the females mature, their posterior part enlarges and
extends out from the root surface.

8. • Single female lays 40-60 eggs
• Approximately 100 eggs are deposited in a gelatinous matrix.
• Males and females undergo four moults, but the males
remain outside of the root and do not feed.
• North india – population peak at April-October
• Coarse textured soils are not favourable for nematode
reproduction

10. Symptoms
• Citrus trees more than 7-8 years old exhibit decline symptoms
causes slow decline
• Which are manifested by yellowing of leaves, defoliation,
• Premature shedding of fruits, reduction in the number and
size of fruits,
• Increasing number of dead twigs from top and weak seasonal
flushes
• Infested roots appear dark, heavily infected roots are covered
with soil particles which do not go inspite of washing

12. Interaction with other pathogens
The incidence of fungal pathogens Fusarium solani &
Fusarium oxysporum is enhanced in the presence of citrus
nematode resulting in root decay and lowering the tree cavity

13. Control
• Nursery should be raised in nematode free soil (fumigated), or away from
the established citrus orhards.
• Treat the basin area with carbofuran @ 4kg a.i./ha just before flowering.
Pulverise the nematicide in the soil followed by light irrigation.
• Intetculture of onion, garlic or marigold in the citrus orchards not only
reduces the nematode population but also provides additional income.
• Incorporation of neem cake @ 1kg/tree along with carbofuran @2kg
a.i./ha in the basin area helps in economizing nematicidal use.
• Some clones and hybrids of trifoliate orange, Poncirus trifoliata are
resistant to citrus nematode and can be used as root stock.