DIAGNOSTIC FARMER‘S FIELD GUIDE FOR FUNGAL DISEASES OF PADDY Next

DIAGNOSTIC FARMER‘S FIELDGUIDE FOR FUNGALDISEASES OF PADDY

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Major Fungal Diseases: Blast

DIAGNOSTIC FARMER‘S FIELD GUIDE FOR FUNGAL DISEASES OF PADDY

Sheath blight

Brown spot

Sheath rot

Foot rot

False smut

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Blast of Paddy

Local Name: Dhwasa rog (Tripura)

Causal organism : Pyricularia grisea ( Magnaporthe grisea )

Leaf blast Node blast Neck blast


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Diagnostic Symptoms

The disease symptoms appear on leaf, leaf sheath as brown spindle shaped lesions at all stages of crop growth.

The central portion of the lesion shown dull grayish colour with pale brown margin.


The disease occur in 3 phases i.e. Leaf blast, Node blast and Neck blast or Panicle blast.

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In case of Leaf blast symptom spindle shaped or eye shaped spots appear on the leaf and several diseased spots may coalesces and show burning effect of entire leaf blade.


Diagnostic Symptoms

In case of neck blast ear head gets infection and turns into black spots girdling, which causes dropping of ear head and cause maximum damage of the crop.

In case of Node blast infection symptom appear on the node portion of the culms and may break the affected nodes.

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Epidemiology

Conditions that favour disease development are sowing of diseased seeds, poor air flow and poor sunlight penetration and rainy days with high humidity


Minimum night temperature range of 20o to 26oC along with high RH 90% for one week at susceptible stage of crop outbreaks the disease.

The plants of rice are very susceptible at seedling stage, rapid tillering stage and ear emergence stage.

Conditions conducive for rice blast include long periods of free moisture where leaf wetness is required for infection.

Excessive application of nitrogenous fertilizers favour the disease

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Brown spot of Paddy

Local Name: Badami Daag Rog (Tripura)

Causal organism : Cochliobolus miyabeanus

Brown spot symptoms on rice leaf and grains.


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Diagnostic Symptoms


The disease is very common in rice growing area.

Epiphytotic form of disease caused Bengal famine during 1942.

The disease is soil and seed borne and disease seeds show poor germination

Disease spot on leaf surface resulting weakening of the plants.

The disease symptoms appears on all parts of paddy plant as innumerable, dark brown, oval spot.

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Diagnostic Symptoms

In severe infection these spots may coalesce and spread all over the leaves.

The panicles may infect and fail to emerge from the sheaths.

The grains of infected panicles become shriveled and discolored.

If grain forms test bitter.

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Epidemiology


Heavy continuous rain with days of cloudy weather are favorable for the development and spread of the disease.

Deep sowing of seeds favour high seedling infection.

Disease increases with the age of plant.

Nitrogen and potash deficiency favors the disease intensity.

Rice variety with thick epidermal cells, thick cuticular layer and larger numbers of silicate epidermal cells are resistant to disease.

High temperature and moisture in a cloudy weather favour quick spread of the disease in the field.

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Sheath blight of Paddy

Local Name: Khola Dhwasa (Tripura)

Causal organism : Rhizoctonia solani

Sclerotia of rice sheath blight

disease


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Diagnostic Symptoms


The disease symptoms appear as oval or elliptical green grayish colour lesions with dark brown margin on the leaf sheaths at just above the water level.

Occasionally the disease spread upto leaf blade and affected leaf dry up from the tip.

The grains, if produced are shriveled and poorly filled.

Brown mustard seed size sclerotia of the fungi are observed on the infected area of the plant.

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Epidemiology


Microclimatic conditions of low sunlight, humidity near 95%, and high temperature (28-32oC) favour the disease.

Disease development is most rapid in the early heading and grain filling growth stages.

Soil borne sclerotia, and to a lesser degree mycelium in plant debris, are means of pathogen survival between crops and are the primary inoculam.

Sclerotia floating in the paddy field and infection occur near the water line.

Sclerotia survive long periods in temperate rice production areas and tend to accumulate in the soil. Buried sclerotia are viable after two years.

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Sheath rot of Paddy

Local Name: Khola pocha (Tripura)

Causal organism : Acrocylindrium oryzae

Symptoms of rice sheath rot disease.


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Diagnostic Symptoms


The disease symptom appear at booting stage of crop.

The characteristic symptoms is the development of irregular lesions with grey centres and brown margins on the flag leaf sheaths.

The lesions increases in size, spread and ultimately rotten spots observed.

The panicles partially opened from the infected sheath, in case of severe infection panicles failed to emerge or rotten completely.

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Epidemiology

Night temperatures of 20°C, dew (mist), cold weather, high humidity, more use of Nitrogenous fertilizers are favorable for development of this disease.


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Bakanae or foot rot of Paddy

Local Name: Gora pocha (Tripura)

Causal organism : Gibberella fujikuroi (Fusarium moniliforme)

Bakanae infected rice plant and field


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Diagnostic Symptoms


The disease may appear in nursery

The diseased seedlings may be stunted, pale, thin and sometimes lanky but subsequently collapse and die.

In the main field typical symptoms are the excessive elongation of stem that can be easily identified from distant place by observing, pale, thin and lanky growth of the diseased tillers.

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Diagnostic Symptoms

Adventitious roots are observed on the nodes above the ground level but basal portion of plants rotten due to fungal attack.

Disease infected hills usually produce less tillers and ultimately die, if survive diseased tillers do not produce ear head and grains.

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Epidemiology


The disease is soil and seed borne.

High nitrogen application favour the disease.

Temperature ranging from 30 to 35° C favour the disease.

Wind or water act as carrier of the spores from one plant to another.

Seedling and tillering stages of the rice crops are more susceptible.

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False smut or green smut of Paddy

Local Name: Laxmi leda (Tripura)

Causal organism : Ustilaginoides virens (Claviceps oryzae)

Symptoms of False smut on rice grains.


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Diagnostic Symptoms


The disease symptoms observed only on the ears.

Individual or infected ovaries are transformed into large, velvety, yellow to orange green masses which are round or oval in shape.

A few grains in ear head are covered with powdery masses and disseminated by air and cause infection of healthy flowers

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Epidemiology


High rainfall favours the disease intensity.

Application of high doses of nitrogenous fertilizers at flowering stage of crop induces high incidence of disease.

Rainfall accompanied by cloudy days are favourable for disease development.

Vulnerable period of disease development and spread are between flowering and maturity of grain.

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