nematology part 2 of pp-202
Post on 13-Feb-2018
221 Views
Preview:
TRANSCRIPT
-
7/23/2019 Nematology Part 2 of PP-202
1/32
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).
-
7/23/2019 Nematology Part 2 of PP-202
2/32
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.
-
7/23/2019 Nematology Part 2 of PP-202
3/32
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
-
7/23/2019 Nematology Part 2 of PP-202
4/32
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
-
7/23/2019 Nematology Part 2 of PP-202
5/32
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
-
7/23/2019 Nematology Part 2 of PP-202
6/32
ROOT-KNOT NEMATODE
Order: Tylenchida
Family: Heteroderidae
-
7/23/2019 Nematology Part 2 of PP-202
7/32
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.
-
7/23/2019 Nematology Part 2 of PP-202
8/32
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.
-
7/23/2019 Nematology Part 2 of PP-202
9/32
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 -
7/23/2019 Nematology Part 2 of PP-202
10/32
Disease Cycle
http://www.apsnet.org/Education/LessonsPlantPath/RootKnotNema/discycleFull.htm -
7/23/2019 Nematology Part 2 of PP-202
11/32
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.
-
7/23/2019 Nematology Part 2 of PP-202
12/32
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.
-
7/23/2019 Nematology Part 2 of PP-202
13/32
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.
-
7/23/2019 Nematology Part 2 of PP-202
14/32
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
-
7/23/2019 Nematology Part 2 of PP-202
15/32
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
-
7/23/2019 Nematology Part 2 of PP-202
16/32
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.
-
7/23/2019 Nematology Part 2 of PP-202
17/32
Seed Gall Nematode
(Wheat Nematode or Ear Cockle)Anguina tritici
Order: Tylenchida
Family: Anguinidae
-
7/23/2019 Nematology Part 2 of PP-202
18/32
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.
-
7/23/2019 Nematology Part 2 of PP-202
19/32
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.
-
7/23/2019 Nematology Part 2 of PP-202
20/32
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.
-
7/23/2019 Nematology Part 2 of PP-202
21/32
-
7/23/2019 Nematology Part 2 of PP-202
22/32
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.
-
7/23/2019 Nematology Part 2 of PP-202
23/32
Kingdom: Animalia
Phylum: Nematoda
Order: Tylenchida
Superfamily: Tylenchoidea
Family: Heteroderidae
Genera:
1. Meloidogyne
2.Heterodera
3. Globodera
CYST NEMATODES
-
7/23/2019 Nematology Part 2 of PP-202
24/32
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
-
7/23/2019 Nematology Part 2 of PP-202
25/32
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.
-
7/23/2019 Nematology Part 2 of PP-202
26/32
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.
-
7/23/2019 Nematology Part 2 of PP-202
27/32
-
7/23/2019 Nematology Part 2 of PP-202
28/32
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
-
7/23/2019 Nematology Part 2 of PP-202
29/32
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.
-
7/23/2019 Nematology Part 2 of PP-202
30/32
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.
-
7/23/2019 Nematology Part 2 of PP-202
31/32
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.
-
7/23/2019 Nematology Part 2 of PP-202
32/32
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
top related