1. Root diseases
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2. 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.
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.,
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.
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3. 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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4. 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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5. Control: 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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6. Root rot: Casual organisms:
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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7. Ganoderma root rot: Symptoms: Control:
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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8. 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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9. 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 thinner roots.
The tap root is usually sticky and moist, with the bark shredded and the woody tissues discolored yellow.
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10. 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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11. Club root: Symptoms: Control:
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:
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.
Mercuric chloride, mercurous chloride and tetrachlor provide control of the disease.
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12. Root wilt:
Usually the disease affects the grown up palms, but palms up to the age of two years are also affected.
Symptoms:
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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13. The newly formed leaves are in small in size.
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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14. 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: 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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15. 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.
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