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

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

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

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

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.

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

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

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).

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)..

MOULTING

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)

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

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

Migratory ectoparasitic Migratory endoparasitic Sedentary endoparasitic Semiendoparasitic

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

Migratory ectoparasitic

These are motile and feeds on external surface cells of roots.Eggs are laid in soils onlyAll 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 systemEx: Stubby root nematode

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).

ECTOPARASITIC ENDOPARASITIC

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.

soybean cyst nematode (Heterodera glycines

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

Many nematode species are able to surviveunder extreme abiotic conditions at very low or high soil temperatures (McSorley, 2003; Treonis and Wall, 2005) or at 0% relative humidity (Wall and Virginia, 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)

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)

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)

CRYPTOBIOSIS OR QUIESCENCE ’

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

PORE SIZE

Nematodes movement is influenced by pore size.

Pore size must be more than width of nematode body (20µ m).

Ideal soils: Sandy loam soils

Sandy soils: Less porosity & Less total pore volume

Clay soils : Greater porosity & Greater total porevolume

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.

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

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

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.

Particle Size(μm) Final population

2 360 139

850 179

534 291

373 1020

250 1174

Sandy loam 1590

Soil moisture % Survival (%)

0 18.4

5 24.8

10 28.0

15 27.3

20 24.0

25 21.1

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.

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

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.

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.

THANK YOU

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)