nematode biology& ecology

1. WELCOME

2. The science of life of
living organisms
including their
structure, function,
growth, origin,
evolution and
distribution

3.  Nematodes are dioceous or
amphigonus
 Male and female nematodes
occur in most species, but
reproduction without males is
common.
 some species are
hermaphroditic .
 Parthenogenesis:
Eg. Meloidogyne,
Heterodera, Tylenchulus.
Intersexes are found in some
genera like Meloidogyne and
Ditylenchus

4.  The plant parasitic nematodes have 6 stages
in their life cycle.They are
1. Egg
2. First stage larva/juvenile (J1)
3. Second stage larva/juvenile (J2)
4.Third stage larva/juvenile (J3)
5. Fourth stage larva/juvenile (J4) and
6. Adult

6. Embryogenesis occurs in two stage
in the first half of embryogenesis
Most of the cell division occurs.
In the second half,
the Embryo elongates markedly and synthesizes the cuticle

7. Egg
 is ovoid-shaped with 3 layers
and contains a single juveniles.
 The majority of eggs are of
similar size (50–100 μm long and
20–50 μm wide) and morphology.
 Eggs between 50 and 500 eggs
per female, depending on the
nematode species and their
environment, but some can
produce more than 1,000 eggs.
 Juveniles hatch from eggs that are
laid by the adult female
 These juveniles are similar to
adults.

8. CHAIN OF EVENTS FROM EGG TO EGG
Female lays eggs Eggs hatch
Juveniles moves at
random in soil wander
to root zone by
physical and chemical
stimuli,aggregate at
root surface
Penetration, invasion
of
tissue,moults,adults

9. The length of the life cycle varies
considerably, depending on
nematode species, host plant, and
the temperature of the habitat.
Generally Life cycle from egg to
egg completes in 20-40 days .
Ex; 1month :RKN
2weeks:foliar nematode
1year :dagger nematode
During summer months when soil
temperatures are 80 to 90ᵒF, many
plant nematodes complete their life
cycle in about four weeks

10. MOULTING
 Increase in body size as growth takes place between moults.
 The cuticle is shed and replaced four times during the life cycle.
 some species of Longidorus and Xiphinema have only three
juvenile stage.
 In Aphelenchus hamatus, the moulting process from fourth-
stage juvenile (J4) to adult took 12–13 h to complete (Wright
and Perry, 1991).

11. In general, the process
involves three phases:
(i) the separation of the old cuticle from
the epidermis (apolysis);
(ii) the formation of a new cuticle from
the epidermis; and
(iii) the shedding of the old cuticle
(ecdysis)..

12. MOULTING

14. HATCHING
Essentially, the hatching process can be divided into three phases:
 changes in the eggshell;
 activation of the juvenile; and
 eclosion (or hatch from the egg).
 In many species, such as Meloidogyne spp., activation of the juvenile
appears to precede, and may even cause, changes in eggshell
structure.
 in others, such as G. rostochiensis, alteration of eggshell permeability
characteristics appears a necessary pre-requisite for metabolic, and
consequent locomotory changes in the juvenile.
 Hatching of nematodes is reviewed in detail by Jones et al. (1998) and
Perry (2002)

15. Flow diagram showing events in the hatching
process of second-stage juveniles
of Globodera rostochiensis after stimulation with
potato root diffusate
 Hatch stimulation
 Unhatched quiescent juvenile in cyst
 Ca2+-mediated change in eggshell
permeability
 Loss of trehalose from the perivitelline fluid
 Uptake of water by juvenile
 Juvenile becomes metabolically active

16. Enhanced juvenile
activity
Exploratory stylet
probing
Sub-polar slit cut in
eggshell by stylet
Juvenile hatches from
the egg
Further water uptake to
full hydration
Emergence of juvenile
from the cyst

17.  Migratory ectoparasitic
 Migratory endoparasitic
 Sedentary endoparasitic
 Semiendoparasitic

18. Ectoparasitic Nematodes
 Remains outside of the plant
and uses its stylet to feed from
the cells
 Uses strategy by which they
can graze on numerous plants.
 Very susceptible to
environmental fluctuations and
predators.
 Have extremely long stylets

19. Migratory ectoparasitic
These are motile and feeds on
external surface cells of roots.
Eggs are laid in soils only
All moults takes place in soils
/root.
All stages are motile and feeds
on roots.
Causes terminal galls in the
roots and cause severe stunting
of the root system
Ex: Stubby root nematode

20. Migratory Endoparasitic
Nematodes
 Spend much of their time migrating through root
tissues destructively feeding on plant cells .
 Cause massive plant tissue necrosis.
 All motile stages are infective.
 Secondary infection by bacteria and fungi
(Zunke 1991).
 Examples are Pratylenchus (lesion nematode),
Radopholus (burrowing nematodes) and
Hirschmanniella (rice root nematode).

21. ECTOPARASITIC ENDOPARASITIC

23. Sedentary Endoparasitic
 Most damaging nematodes in the
world have a sedentary endoparasitic
life style.
 The cyst nematodes (Heterodera and
Globodera) and the root-knot
nematodes (Meloidogyne).
 Juveniles becomes sedentary
because their somatic muscles
atrophy.
 The juveniles feed, enlarge and molt
three times to the adult stage.
 The large feeding cells formed by
these nematodes plug the vascular
tissue of the plant making it
susceptible to water stress.

24. soybean cyst nematode (Heterodera glycines

25. Semi-Endoparasites:
Nematodes
 They are able to partially
penetrate the plant and feed at
some point in their life cycle.
 nematodes swell and do not
move.
 risk of death if their host plant
dies
 EX: Rotylenchulus reniformis,
 Tylenchulus semipenetrans

26.  Many nematode species are able to survive
under extreme abiotic conditions at very low or
high soil temperatures (McSorley, 2003;Treonis
and Wall, 2005) or at 0% relative humidity (Wall
andVirginia, 1999).
 To survive unfavourable conditions, some
nematodes are able to suspend development
and survive in a dormant state until favourable
conditions return.
 (D.J.Wright and R.N. Perry)

27. DORMANCY
 Subdivided into ‘quiescence’ and ‘diapause’.
 Quiescence is a spontaneous reversible response to
unpredictable unfavourable environmental conditions
and release from quiescence occurs when favourable
conditions return.
 Quiescence can be facultative or obligate.
 Adverse environmental conditions and the types of
quiescence they induce include
 Cooling (cryobiosis), high temperatures (thermobiosis),
lack of oxygen (anoxybiosis), osmotic stress (osmobiosis)
and dehydration, or desiccation, (anhydrobiosis).
(D.J. Wright and R.N. Perry)

28. DIAPAUCE
 Is a state of arrested development.
 For cyst and root-knot nematodes it is a strategy
to overcome cyclic long-term conditions .
 Obligate diapause is initiated by endogenous
factors and can be relieved by the J2 receiving
exogenous stimuli for a required period of time.
 Nematodes can undergo obligate diapause only
once in their life.
 Facultative diapause is initiated by exogenous,
rather than endogenous, stimuli and terminated
by endogenous factors after a critical period of
time (D.J. Wright and R.N. Perry)

29. CRYPTOBIOSIS OR QUIESCENCE ’

30.  Ecological factors influencing nematode
ecology (soil pore size, aeration,
temperature, pH , light, moisture, osmotic
pressure, chemicals, decomposing plant
material ).

31. PORE SIZE
 Nematodes movement is influenced by pore size.
 Pore size must be more than width of nematode body (20
µ m).
 Ideal soils: Sandy loam soils
 Sandy soils: Less porosity & Less total pore volume
 Clay soils : Greater porosity & Greater total pore
volume
 Rode : showed that the migration of juveniles of
Globodera rostochiensis toward potato plants
was greatest in sandy soil, intermediate in loamy
soil, and least in clay soil.

32. SOIL AERATION
 Oxygen content in aerated soil: 18-21 % , co2 less than 1
%.
 Nematode activity increases with increase in oxygen
concentration but decreases with increase in co2
concentration
 Lowest level of oxygen requirement for host and
nematode : 3-5 %
 Detrimental level to nematodes is above 5%
 Eg: xiphinema americanum more sensitive to long oxygen
exposure
 the aeration and pore size of sandy soils increase
nematode viability

33. Moisture
 Either too high or too low moisture levels affects the
nematode
 Tolerance levels to moisture may vary
 RKN & Burrowing nematode sensitive to dessication
 Stem and bulb nematode resistant
 Egg masses, cysts,galls are resistant to high moisture
 Ideal level : Field condition

34.  The effect of soil moisture and soil particle size on the survival and
population increase of Xiphinerna index
(Sufian A. SULTAN and Howard FERRIS)
(Department of Agricultural Sciences, Al1 Najah National University,
West Bank, Israel, and Department of Nematology, University of
California, Davis, CA 95616, USA)
 The interaction of soil moisture on survival and subsequent
reproductive potentiial of Xiphinema index,and the effect of sand
particle size on population increase, were studied under greenhouse
conditions.
 In the absence of a host, fewer than 10 %of the nematodes survived
for 60 days even under favorable (intermediate) moisture conditions.
Survival was very low in both saturated and dry soils.
 In the presence of a host, population increase of the nematode was
highest in sandy loam and in fine sands of 250 μm particle size.
 Population increase was low in coarse sand of particle size534 μm
and larger. Root damage to host plants was directly related to the
increase in nematode population.

35. Particle Size(μm) Final population
2 360 139
850 179
534 291
373 1020
250 1174
Sandy loam 1590

36. Soil moisture % Survival (%)
0 18.4
5 24.8
10 28.0
15 27.3
20 24.0
25 21.1

37. SOIL TEMPERATURE
 Temperature plays a major role in nematode activities like
hatching, reproduction, movement, multiplication,
survival, feeding etc.
 5-15 ºc :most nematodes inactive
 15-30ºc: optimum
 30-40ºc :most nematodes inactive
 Eg : H.rostochiensis
 Invading host : 15-16ºc, cyst emergence : 21-25ºc,
Development : 18-24ºC.

38. pH
 Severely affects hatching
 Variation in nematode activity is mainly due to soil pH.
 Reduction in pH from 6 to 4 decreases the emergence
of juveniles of H. rostochiensis.
 At 3 and 10.6 juveniles of RKN juveniles repells
 Inhibitory levels are < 5 and > 8
 E.g.. P . Penetrans opt :5.5-5.8
LIGHT
Light has no or little effect on phytonematodes
Mostly spend their lives in darkness
UV light is known to be lethal

39. OSMOTIC PRESSURE
 Juveniles of H.schactii shrink in conc NaCl solution.
 OP may act as stimulating agent eg. more RKN in high saline soils.
 Exposure of RKN juveniles to 1M salt solution ineffective.
 Osmotic destruction of nematodes eg. M.arenaria.
 Most nematodes can tolerate upto 10 atmosphere.

40. HOST AND SOIL
CHEMICALS
 Addition of nitrogenous compounds to soil decrease the
population of nematodes.
 Eg P.penetrans .
 Applications of sodium nitrate and ammonium nitrate to
soil reduced hatching, penetration and cyst development
in H.glycines on soyabean.

41. THANK YOU

42. References
 Reproduction, Physiology and Biochemistry
DENIS J. WRIGHT1 AND ROLAND N. PERRY2
© CABI 2006. Plant Nematology (eds R.N. Perry and M. Moens)
(Division of Biology, Faculty of Life Sciences, Imperial College London)
 The effect of soil moisture and soil particle size on the survival and
population increase of Xiphinerna index
Sufian A. SULTANa nd Howard FERRIS
(Department of Agricultural Sciences, Al1 Najah National University,
West Bank, Israel, and Department of Nematology, University of
California, Davis, CA 95616, USA)
The History of Nematodes
Blaxter, M.L., P. De Ley, J.R. Garey, L.X. Liu, P. Scheldeman, A. Vierstraete,
J.R. Vanfleteren, L.Y. Mackey, M. Dorris, L.M. Frisse, J.T. Vida, K.W.
Thomas, K.W. 1998.
(A molecular evolutionary framework for the phylum nematoda)