Transcript 6.root diseases

Root diseases
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Introduction:
•
Root diseases are the diseases that infect the root portion.
•
Since root is the main portion of the plant, any infection in
root will affect whole plant.
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There are different types of root rot e.g. wet root rot, dry root
rot, black root rot, red root rot and santavory root rot etc.,
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In root disease, pathogens infect the root and causes
decaying of root cells.
•
The pathogens are mainly soil borne and seed borne in
nature and its spreads through the soil, implements/
irrigation water.
Cont…
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Sometimes pathogen produces resting structure (sclerotia) or
specialized structure (rhizomorph) which helps in spreading over a
distance.
These root disease, in the earlier stages of
symptom expression could be managed by
drenching of fungicides around the root portion.
In case of severe infection,
spreading of the pathogen could be
controlled by drenching around the
infected plants/ tree.
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Dry root rot:
Symptoms:
• The first symptom of the disease is
yellowing of the leaves.
• Within a day or two, such leaves droop
and in the course of the next two or three
days, they may drop off.
• The plants may wilt within a week after the
first symptoms show.
• When the stem is examined closely, dark
lesions may be seen on the bark at the
ground level.
• If the plants are pulled from the soil and
examined, the basal stem and the main
roots may show dry rot symptoms.
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The tissues are weakened and break
off easily.
In advanced cases sclerotial bodies
may be seen on affected soil.
Control:
Since the casual organism
is soil borne, it is difficult to
control the disease.
Drenching the affected plants and the
infested soil with Bordeaux mixture or
other effective fungicides may help
reducing the inoculums of potential.
Development of resistant crop varieties
against the disease has not been
successful.
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Root rot:
The pathogen s is soil dwellers, attacking the
roots and spreading upwards to the basal
portion of the stem, causing the plant to wilt.
Casual organisms:
 Ganoderma root rot
 Phytophthora parasiti
 Rhizoctonia bataticola
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Ganoderma root rot:
Symptoms:
Ganoderma root rot the stem becomes
soft and rots.
With the death of the stem tissues, the
fungus spreads rapidly and forms the
bracket – like fruiting body on the sides
of the stem.
Control:
The area of the diseased plant should be isolated by
trenching and the plant should be cut and burnt.
The remaining ones should be given a protective coating
on the trunk with Bordeaux paste and the soil around the
stem drenched with Bordeaux mixture.
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Phytophthora root rot:
Symptoms:
• The first symptoms of the disease are yellowing
of the leaves, which later turns olive brown
colored.
• plant wilts from the tip downwards.
• When the plant is pulled out the roots appear
dark and in the process of decaying.
Control:
A prophylactic treatment with Bordeaux mixture
or any other fungicidal drench may help check
the incidence of disease.
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Rhizoctonia root rot:
Symptoms:
The chief symptom is a sudden
and complete wilting of the plants.
The disease spreads in the field in
concentric circles.
If the affected plants are pulled out
and examined, the entire roots system
may be found rotting, the decay being
more complete on the lateral and The tap root is usually sticky and
moist, with the bark shredded and the
thinner roots.
woody tissues discolored yellow.
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Cont…
In some cases the rotting may spread to the basal stem,
causing shredding of the bark and formation of sclerotial
bodies.
Control:
Certain cultural practices have been recommended to provide
unfavorable soil conditions for the pathogens.
Adjusting the sowing dates so that the crop is not in the field when
soil temperature are high, has given good control.
Mixed cropping to include shady plants with cotton to reduce the
soil temperature has also helped in checking the disease intensity.
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Club root:
Symptoms:
The disease symptoms become apparent
only after the pathogen has advanced
considerably in the root system.
The above ground plant parts show shunting,
reduction in the size of head, or chlorosis and
other general non specific unhealthy
symptoms.
Control:
Mercuric
chloride,
mercurous chloride and
tetrachlor provide control of
the disease.
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The disease is severe in acidic
soils; hence application of lime to
increase the soil pH, particularly in the
hilly areas where cabbage is grown, is
recommended by several workers.
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Root wilt:
Symptoms:
Usually the disease affects the grown
up palms, but palms up to the age of
two years are also affected.
Symptoms are first visible on the
leaves of the middle whorl as a
general wilting and extend to the outer
whorl the leaves.
The leaflets are bent abnormally and
this called “ribbing” of leaflets or
flaccidity, a typical characteristic of the
disease.
Gradually these leaves turn yellow and
exhibit marginal necrosis.
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Cont…
In older palms, flaccidity is followed
immediately by foliar yellowing and
necrosis.
The newly formed leaves are in small in size.
The root system of the affected palms
starts decaying.
Its starts from the tip and spread
upward.
In the affected palms, nearly 90 per
cent of the roots exhibit symptom of
decay.
In few cases, the root system appears
apparently healthy but the absorbing region
gets covered with a hard hypodermis.
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Control:
As the etiology of the disease is still
uncertain, controlling the disease
continues to be based on sanitation
and cultural practices.
Removal of severely diseased and
uneconomical palms and replanting
with high yielding hybrids are
recommended.
For each tree, application of the
following manuring is suggested: 2550 kg FYM or green leaf; N (.0.34kg),
P (0.17 kg), K (0.68kg) in the form of
urea, ultraphos and muriate of potash
and 2 kg of dolomite or 1 kg lime and
500 gm of magnesium sulphate.
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To sum up
Root diseases are the diseases that infect the root portion, and any
infection in roots will affect whole plant.
There are different types of root rot e.g. wet root rot, dry root rot, black
root rot and red root rot etc., In root diseases, pathogens infect the root
and causes decaying of root cells.
The pathogens are mainly soil borne and seed borne in nature and its
spreads through the soil, implements/ irrigation water.
Sometimes pathogen produces resting structure (sclerotia) or
specialized structure (rhizomorph) which helps in spreading over a
distance.
These root disease, in the earlier stages of symptom expression could
be managed by drenching fungicides around the root portion.
In case of severe infection, spreading of the pathogen could be
controlled by drenching around the infected plants/ tree.