Nematology Part 2 of PP-202

7/23/2019 Nematology Part 2 of PP-202

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Introductory Plant NematologyNematodes that attack plants are worms, mostly

microscopic in size, ranging from 0.25 mm to 3.0

mm long where as (1/100-1/8 inch)of body length in

diameter. Cylindrical in shape, tapering toward the

head and tail. Females of a few species lose their

worm shape as they mature, enlarged in diameter and

assuming varying forms, such as pear, lemon, or

kidney shapes. Plant parasitic nematodes possess all

of the major organ systems of higher animals except

respiratory and circulatory systems. (multicellular,

microscopic, worm like or thread like organisms

tapering at both ends belonging to animal kingdom

having all the physiological systems except circulatory

and respiratory).


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Life Cycle and Reproduction

Plant parasitic nematodes have a simple life cycle of six

stages: egg, four juvenile stages, and adult (male

female). The embryo develops inside the egg to

become the first-stage juvenile. The first-stage

juvenile molts inside the eggshell to become a

second-stage juvenile, which hatches from the egg,

and in most species must feed before continuing to

develop. The nematode molts three more times to

become a fully developed adult. Male and female

nematodes occur in most species, and both may be

required for reproduction. However, reproduction

without males is common, and some species are

hermaphroditic(females, produce both sperm and eggs).

The length of the life cycle depend

on nematode species, host plant

and the temperature, their life

cycles is completed in about 27

days at 28 C.


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Nematode Feeding

Plant parasitic nematodes feed on living plant

tissues. All have some form of oral stylet

or spear, which is used somewhat like a

hypodermic needle to puncture the host

cell wall.

Ectoparasitic: Nematodes may feed on plant

tissues from outside the plant. Endoparasitic:

(or inside the tissues).

MigratoryIf the adult female moves freely

through the soil or plant tissues.

Migratory Endoparasites Migratory

endoparasites can move into, through, and out

from host tissues at any stage of development


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Above-Ground Symptoms

These are rarely, if ever, sufficient evidence to

diagnose a root nematode problem. However,

they are important because possible nematode

problems are almost always first noticed

because of abnormal top growth. Certain kinds

of symptoms are typical of nematode injury to

roots, and should always make one consider

nematodes as a possible cause for the inferior

performance. They can also be used to help

locate the most severely affected areas in the

planting after the problem is diagnosed. Since

most plant nematodes affect root functions,

most symptoms associated with them are the

result of inadequate water supply or mineral

nutrition to the tops: chlorosis (yellowing) orother


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abnormal coloration of foliage, stunted top growth, failure to

respond normally to fertilizers, small or sparse foliage, a

tendency to wilt more readily than healthy plants, and slower

recovery from wilting.

Woody plants in advanced stages of decline incited by nematodes

will have little or no new foliage when healthy plants have

substantial flushes, and eventually exhibit dieback of

progressively larger branches. "Melting out" or gradual decline

is typical of nematode-injured turf and pasture. Plantings which

are stunted by nematodes often have worse weed problems

than areas without nematode injury, because the crop is less

able to compete with weeds than it should be.

Below-Ground Symptoms

These may be more useful than top symptoms for diagnosing many

nematode problems. Galls, abbreviated roots, necrotic lesions

in the root cortex, and root rotting may all help in diagnosing


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ROOT-KNOT NEMATODE

Order: Tylenchida

Family: Heteroderidae


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Introduction

Root-knot nematodesare plant-parasitic nematodes from the

genusMeloidogyne. Root-knot nematodes are distributed worldwide, and are

obligate parasites of the roots of thousands of plant species

About 3000plants are susceptible to infection by root-knot

nematodes. Root-knot nematode larvae infect plant roots, causing the

development of root-knot galls that drain the plant's

photosynthateand nutrients.

Infection of young plants may be lethal, while infection ofmature plants causes decreased yield.


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Symptoms

As a result of nematode feeding, large galls or "knots" can beseen throughout the root system of infected plants.

The degree of root galling generally depends on threefactors:

1. Nematode population density.

2. Meloidogynespecies and race.

3. host plant species and even cultivar.

Large numbers of nematodes penetrating roots in close

proximity also will result in larger galls.


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Nematode damage symptoms
http://www.apsnet.org/education/LessonsPlantPath/RootKnotNema/text/fig08.htmhttp://www.apsnet.org/education/LessonsPlantPath/RootKnotNema/text/fig04.htmhttp://www.apsnet.org/education/LessonsPlantPath/RootKnotNema/text/fig06.htmhttp://www.apsnet.org/education/LessonsPlantPath/RootKnotNema/text/fig07.htmhttp://www.apsnet.org/education/LessonsPlantPath/RootKnotNema/text/fig05.htmhttp://www.apsnet.org/education/LessonsPlantPath/RootKnotNema/text/fig03.htm


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Disease Cycle
http://www.apsnet.org/Education/LessonsPlantPath/RootKnotNema/discycleFull.htm


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Management

Use of cover crops. Cover crops can be grown outsideof the normal agricultural growing season, and someare antagonistic to nematodes.

Floodingand solarization of fields.

Fumigants (such as 1, 3-dichloropropene, methyl

bromide and dazomet) are commonly applied as pre-plant treatments to reduce nematode numbers.

In tomato, genetic resistance to root-knot nematodes isconferred by the Mi gene which was obtained fromLycopersicon peruvianum.

Root-knot nematodes (Meloidogynespp.) can becontrolled with abiocontrol agents, i.e. Paecilomyceslilacinus A bacterium pasteuria penetrans and plantproducts i.e neem leaves and cake.


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Citrus Nematodes

Tylenculus semipenetrans

Order: Tylenchida

Family:Tylenchulidae

Worldwide with that of citrus.

Occurs in 95% of citrus in California and is common in all citrus-growing

areas.

Originally spread with planting stock and further with irrigation water.


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SYMPTOMS

Similar to poor nutritional

symptoms.

Reduction of terminal growth,

chlorisis, shedding of leaves, dieback of branches.

Reduction in number and size of

fruits.

Roots are of brown color and dirtydue to adherence of soil particles.

Destruction of roots is due to

secondary invasion offusarium sp.


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Tylenchulus semipenetranscompletes its life cycle within 4-6 weeks.

It moults 4 times to become adult.

After first moult within egg 2

nd

stages larvae moult three times.

Larvae feed on epidermis, Hypodermis and cortical tissues.

Young female penetrates deeply in root cortex

Nematodes feed on the cells in which head is located.

Anterior portion of nematode elongates and becomes modified

Posterior portion of the nematodes enlarges greatly.

Eggs are enveloped in a mucous like material which is excreted from.

Life cycle of Citrus Nematode


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Most favourable soil temperature is 20-30 0C the best is 25 0C.

Nematodes larvae survive more than one year at 15 0C in moist soil.70% larvae

may survive at 10 0C for 24 months in-vitro.

Favourable soil pH is 6.00-8.00.

Moderate amount of clay, silt and organic matter favour development and infection.

Environmental factors Affecting

Parasitism


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MANAGEMENT

Nursery seedlings should be planted in plastic bags.

These bags should be placed on raised wooden benches.

Soil used for nursery should be disinfected with formalin.

All nurseries must be registered with any institute who can give recommendation.

Proper Phyto-sanitation practices should be adopted.

Treatment of nursery beds with nematicides/ bio-products.

The pits where seedlings are being planted should be treated with nematicides.(furadon and Rugby).

Flood irrigation should be replaced with drip irrigation to avoid spread of nematodes.

While Replanting at the spot of dead plant the roots of dead plant should be

completely removed and pits should be treated with nematicides.


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Seed Gall Nematode

(Wheat Nematode or Ear Cockle)Anguina tritici

Order: Tylenchida

Family: Anguinidae


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Introduction

Seed gall nematodes (Anguinaspp.) were the first plant-

parasitic nematodes to be described in the scientific literaturein 1743.

Nematodes migrate as J2sin water films to the leaves of

plants where they feed as ectoparasites at the tips, causing

distortion of the leaves.

Plant starts to flower the J2 penetrates the floral primordia andstarts to feed on the developing seed.

In the seed the nematode undergoes molting, continues to feed,and eventually kills the seed to form a blackened "cockle"(seed gall).

The nematodes in the seed gall can survive for 30 years if keptin a dry location.

When proper moisture and temperature conditions arise,

the cryptobiotic J2becomes active and start their life cycle

over again.


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Symptoms

Distorted leaves and stems are evident prior to heading.

As diseased plants approach maturity, galls are formed

in the florets, replacing the kernels.

The galls are similar in shape to the seed they replace

and are dark brown in color.

Large numbers of motile larvae are present within the

galls and become active after the galls have been moistened.


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LIFE CYCLE

Juveniles penetrate flower primordia and develop through the

third and fourth stages to adulthood.

Galls can develop from undifferentiated flower buds, stamen

tissues, and various other tissues.

Galls contain up to 80 adults in a 1:1 sex ratio.

Reproduction is amphimictic; females produce up to 2000

eggs per individual over several weeks.

Galls fall to the ground, absorb water, and release juveniles in

springtime, or galls may be harvested and stored with

seed. Juveniles within drying galls can enter a cryptobiotic

state; viable juveniles have been recovered for up to periods as

long as 38 years.

Galls appear darker, shorter, and thicker than seed kernels.

For nematodes forming seed galls, one generation is produced

per year.


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Management

Crop rotation for 1 to 2 years to a non-host eliminatesA.

triticifrom the soil. The nematode does not survive by

feeding on fungi.

Seed can be cleaned by placing it in a 20%brine

solution; galls float to the surface where they can be

separated.

The seed is then rinsed and dried (heat treated).

Mechanical separation also effective in removing galls

from seed. There are no resistant varieties of wheat.


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Kingdom: Animalia

Phylum: Nematoda

Order: Tylenchida

Superfamily: Tylenchoidea

Family: Heteroderidae

Genera:

1. Meloidogyne

2.Heterodera

3. Globodera

CYST NEMATODES


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Heterodera & Globodera

1. Heterodera shachtii(Sugar beet cyst nematode)

2. Heterodera glycines(Soybean cyst nematode)

3. Heterodera avenae (cereal cyst nematode)

1. Globodera rostochienesis(Golden potato cyst nematode)

2. Globodera pallida (White potato cyst nematode)

Globoderaspp.(=round cyst nematode)

Why they are

called cyst

nematode???

Strong sac like

covering

around the egg

massed called

cyst


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Soybean cyst nematode

D E

Crop symptoms in response to nematode infections, A: Sugar beet field infected with beet cyst nematodes (H.

schachtii). B: Size reduction of sugar beet roots due to nematode infection. C: Soybean plants infected with soybean

cyst nematodes (H. glycines). D. Different accessions of wheat infected with cereal cyst nematodeHeterodera avenae.E. symptoms of attach ofHeterodera avenae on wheat plants.


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Potato Cyst NematodesGlobodera pall ida Globodera rostochiensis

Potato cyst nematode (PCN) species are distributed world wide and are major and persistent

pests. The nematode was first reported from Germany and since then it has spread all overEurope. It reached the Indian sub continent before 1970 being first reported form India in

1972 and from Pakistan in 1980 (Maqbool, 1980). PCN was first reported in Pakistan in

1980 from Abbottabad.

Symptoms

The above ground symptoms are not very specific; however root injury causes stress and

reduced uptake of water and nutrients results in yellowing and discoloration of leaves.

Stunting and wilting of plants is prominent under drought conditions.

Small immature females of white and yellow color can be seen on the roots at flowering

stage.

When females die they become cysts, and their cuticle become brown containing 300-500

eggs.

The nematodes damage the roots and reduce yield, even when infestations produce no

obvious symptoms in the haulm.

With severe infestations, roots are more seriously damaged and may be killed.

Severely infested plants are stunted, often chlorotic and typically occur in patches.


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Sources Of Spread Mainly introduced by cysts of the nematode in soil attached to

potato tubers, farm machinery or footwear.

They are only rarely introduced by infested tubers. Cysts are also spread locally by wind and flood water.

Life Cycle of Cyst nematode

The active part of the life cycle begins, when the second stage juveniles (J2) emerge form

the eggs after stimulation by substances emanating from host plant roots.

The J2 enter the host roots near the tip and use their stylet to cut through the cell walls,

leaving a trial of ruptured cells.

Their hollow stylet pierces the cell, injects saliva, and later withdraws some cell contents. The saliva induces cell enlargement and breakdown of surrounding cell walls to form a

large, syncytia transfer cell with dense, granular cytoplasm .

Once the juvenile is sedentary, it undergoes three molts to become the adult. Sex is

distinguishable at the start of the third juvenile stage.

The nematode continues to feed until its development is complete a period which


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The nematode continues to feed until its development is complete, a period which

takes 2 to 3 months depending upon temperature.

Fourth stage males remain coiled within the sac like third stage cuticle and emerge

from the root after the final moult.

The males are vermiform , about 1 mm long. They live for about 10 days in the soiland apparently do not feed .

Adult females enlarge as their gonads increase in size, ultimately rupturing the root

cortex and exposing their bodies outside with only their heads embedded in the root. At

this stage the female releases a pheromone that attracts the males.

Fertilization is accomplished when the males coil around the vulvae areas of thefemale.

Each female may undergo multiple mating with many different males.

The female accumulates all her eggs within her body and the embryo develops within

the egg upto the second stage juveniles while still in the females body.

When the female dies, the cuticle forms a though, leathery cyst that can contain up to500 embryonated eggs.

When the potatoes are harvested, the cysts are detached from the roots into soil where

they over winter.

When the next potato crop is planted, exudates from the roots stimulate the juveniles

and life cycle is again initiated.


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A cartoon diagram of life cycle of cyst nematodes. A: J2, J3, J4juveniles in the second, third

and fourth developmental stages (Jung and Wyss 1999), B: Real time picture of J4H. schachtii

female nematode and female associated syncytium in Arabidopsis roots C: Real time picture of

J4male nematode and male associated syncytia.


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When the female of either species dies, its body forms a dark,

reddish-brown cyst with a hard skin. (golden in case G.

rostochiensis)

Each cyst usually contains 200600 eggs. If infested plants arelifted carefully, the swollen females or the cysts appear as

small bead-like objects attached to the roots.

With severe infestations, cysts may occasionally be seen on

the surface of tubers. At harvest, most cysts become detached from the roots and

remain in the soilasa source of infestation for future potatocrops. In the absence of host plants, most eggs hatch within 7

years, and the population declines.

However, some eggs remain viable in the soil for 10 or more

years.


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Management of Potato cyst

Nematodes PCN is difficult to control because the eggs and juveniles in the cyst are

protected from desiccation and chemicals and remain dormant for many

years in the absence of hosts.

It is only when eggs hatch that the nematode can be controlled with

nematicides.

Resistant varieties

Crop rotation is an effective and practical means of control.

However, rotations of up to 10 years are necessary to reduce populations.

Biocontrol agents (e.g.Piriformospora indica)

Use of transgenic crop plants

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Nematology Part 2 of PP-202