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Jul 15, 2015
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)..
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.
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.
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)