Rice Blast Disease in Paddy Crop: Symptoms, Causes, Control Management, and Treatment

Rice is an annual plant harvested after one growing season, and it can reach a height between one and 1.8 meters depending on the variety of rice grown. The leaves of the plant are long and flattened, borne on hollow stems with hollow ends. It is common to see fibrous roots that are broad and spread out. A panicle, or inflorescence (flower cluster), is a cluster of spikelets that bear the flowers that produce the fruit or the grain that the plant produces. Let’s check out more information on rice blast disease in paddy crop below.

Rice Blast Disease in Paddy Crop
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In terms of the size, shape, weight, and overall productivity of a plant, different varieties differ dramatically in terms of the panicle’s length, shape, and weight. In addition to bacterial leaf blights and sheath rots, false smuts, rice blasts, rice tungro diseases, and other diseases, rice crops are susceptible to diseases that often negatively influence yields and grain quality. One of the diseases is called Rice blast disease.

The Rice blast disease is caused by Magnaporthe oryzae (Ascomycota), which occurs in about 80 countries on all continents where rice is grown in paddy fields and upland cultivations. The rice blast disease is caused by a fungus that causes lesions on the leaves, stems, peduncles, panicles, seeds, and even the roots of the rice plant. This disease is so dangerous that it has been rated as one of the most critical plant diseases of the last century due to its potential threat of crop failure.

Rice blast disease in paddy crop

Identification of Rice blast pathogen

A fungus called Pyricularia oryzae causes this disease, and it overwinters in rice seeds and infected rice stubble and is passed from one generation to another. During the next growing season, the reproductive structures of the fungus, the spores, can spread to rice plants from both of these sources, causing new infections to be initiated. Aside from this, the spores from these new infections may also spread to other rice plants over a great distance by wind, which can be very harmful to them. As a result of this pathogen being clustered, conidiophores are produced from each stoma in clusters.

There are usually 2-4 septa on them, and they are rarely found solitary. It can be seen that the basal area of the conidiophores is swollen and taper up to the lighter apex. This fungus has conidia that measure 20-22 x 10-12 micrometers. Two septa are present on each conidium; they are translucent and slightly darkened on the surface. As a result of their inverse clavate shape and tapering at the apex, these cones have a curved shape. In the field, it is rare to come across the perfect stage.

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Paddy Crop
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Symptoms and signs

As one of the symptoms of rice blast, lesions can be noticed on all plant parts, including leaves, leaf collars, necks, panicles, pedicels, and seeds, which show the symptoms of rice blast. According to a recent report, even roots can become infected by bacteria. However, the most common and diagnostic symptom of rice blast, diamond-shaped lesions on the leaves, occurs more often than lesions on the sheaths, making diagnosing the disease difficult.

Symptoms on Rice plant leaves

A variety of symptoms can be seen on the leaves of the host plants depending on the environmental conditions, the plants’ age, and the host cultivars’ resistance levels. On susceptible cultivars, lesions may initially appear gray-green and water-soaked with a darker green border.

As the lesions grow, they will likely become larger, expanding to several centimeters. Older lesions in susceptible cultivars are often a light tan color with necrotic borders when they age. When cultivars resist the disease, lesions tend to remain small, between 1 and 2 mm in size, and brown to black.

Symptoms on Rice collars

In a rice plant, the collar refers to the junction between the stem sheath and the leaf at the top of the plant’s stem. A generalized necrosis area characterizes the collar’s infection at the point at which the two tissues are joined together. As a result of collar infections, the whole leaf can be killed, and the infection may extend into and around the sheath by a few millimeters. The fungus can produce spores on these lesions due to the infection.

Symptoms on Rice necks and panicles

The stem portion of the rice plant rises above the leaves and is responsible for supporting the seed head or panicle that appears in the middle of the plant. Often, the rice blast fungus infects the neck at the node, leading to a condition known as rotten neck or neck blast, which manifests the infection at the node. There can be severe consequences caused by neck infection, such as the seeds not filling up (called blanking) or the panicle falling over, as if rotten, causing the entire plant to fall over.

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Rice blast can cause the panicles to become infected as the seeds are forming due to the fungus. In addition to the panicle branches, spikelets, and spikelets themselves, there are lesions on the panicle. Lesions on panicle branches are usually gray-brown discolorations on the branches, and they may eventually cause the branches to break at the location of the lesions over time.

Symptoms on Rice seeds

The fungus has often isolated from the pedicels of the seeds. As a result of infected pedicels, seeds are not produced; a condition known as blanking occurs when pedicels become infected. In addition, it is usually observed on seeds that rice blast produces brown spots, imperfections, and occasionally a classic diamond-shaped lesion often seen on leaves.

The process which occurs during seed infection by the pathogen and how it occurs have not been thoroughly studied, nor has there been any extensive research into the time the infection occurs. Even so, it has been found that the fungus can infect the florets as they mature into seeds during the maturation process. It is believed to be the primary mechanism by which the seeds become infected.

Monitoring and treatment decisions

The need for treatment should be determined by monitoring the situation. Throughout the growing season, plant leaves should be examined in several locations across the field for leaf lesions; the monitoring should be intensified as the plants approach the boot stage. Treatments may be justified if blast lesions increase just before the boot stage.

It is essential to consider the progress of the disease, the crop growth stage, the environmental conditions, and the variety of rice when making a treatment decision. For example, suppose you grow one of the more susceptible rice cultivars with long periods of leaf wetness and warm night temperatures during the growing season. In that case, there is a greater risk of developing neck and panicle blast infections.

Therefore, when the panicles emerge from the boots, they should be protected as they emerge from the boots by using a protectant fungicide. Despite this, rice blast is a multiple-cycle disease. Therefore, fungicide applications applied early in the season to control leaf blasts are ineffective in reducing rice blast incidences or yield losses due to neck blasts.

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Disease control methods

Cultural methods
  • Planting rice varieties resistant to the rice blast is one of the most practical and economical ways to control the rice blast. ADT 36, ADT 37, ASD 16, ASD 20, ADT 39, ASD 19, TPS 3, White Ponni, ADT 44, IR 64, and IR 36 are some of the varieties proven to be more tolerant.
  • A high level of nitrogen fertilization, aerobic soil conditions, and drought stress are all factors that favor blasts. Therefore, the susceptibility of rice to the disease is increased due to high nitrogen rates and nitrate nitrogen. Additionally, extended drain periods may also encourage the disease by aerating the soil, converting ammonium to nitrate, and causing drought stress to the rice plant. Hence it is advisable to apply nitrogen fertilizer in three split doses to avoid excessive nitrogen application.
  • Identify and avoid blast-infested seeds in areas where the blast is not a problem by sampling and testing seeds in areas where the blast is not a problem. Through this, it may be possible to limit the spread of the disease into areas that are not infested.
  • The use of water seeding is recommended to reduce or eliminate the transmission of disease from seed to seedlings. The use of drill seeding is not recommended due to the possibility of seed transmission, nitrate formation, and drought stress that can occur.
  • For blast development to be limited, it is recommended that continuous flooding is carried out. Field drainage should be avoided, especially for long periods, since this allows nitrate to form and may result in drought stress in fields. The results of some studies in other areas suggest that shallow water is more conducive to blast development than deeper water in some areas.

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Chemical methods
Dry seed treatment

You should add at least 2 grams of Thiram, captan, carboxin, or carbendazim per kilogram of seeds. Before soaking seeds for sprouting, treat them at least 24 hours in advance. Seeds treated with this method can be stored for 30 days without losing viability.

Wet seed treatment

Carbendazim or Tricyclozole can be added to the seed water at a rate of 2 grams per liter of water for each kilogram of seed. You must soak the seeds in the solution for two hours. Drain the solution, sprout the seeds, and sow them in a nursery bed as soon as they have sprouted. As a result of this wet seed treatment, seedlings are protected from seedling diseases such as blast for up to 40 days, and this method is more effective than the dry seed treatment for preventing seedling diseases

Alternatively, the seeds can be treated with a talc-based formulation of P. fluorescens (Pf1) at a rate of 10 grams per kg of seed, soaked overnight in 1 lit of water, and treated the following morning. The excess water should be drained, and the seeds should be allowed to sprout for 24 hours before being sown.

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Paddy Farming
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Seedling dip with Pseudomonas fluorescens

In the main field, stagnate water to a depth of 2.5 cm over a surface area of 25 square meters. The talc-based formulation of Pseudomonas fluorescens (Pf1) should be sprinkled over 2.5 kg of stagnant water and mixed. As soon as the seedlings are taken out from the nursery, they should be soaked in stagnated water for 30 minutes before they are transplanted into the main field.

Chemical compoundDosage per Hectare
Carbendazim 50WP500 grams
Tricyclozole 75 WP500 grams
Metominostrobin 20 SC500 ml
Azoxystrobin 25 SC500 ml


The amount of disease at the end of the growing season’s vegetative phase affects the amount of disease in the reproductive phase of the growing season. It must be noted that managing rice blasts requires vigilance and careful integration of many strategies and techniques that the individual rice producer has learned throughout the world from everywhere. The successful management of rice blasts results from a comprehensive series of recommendations that employ several different management strategies involving techniques within each strategy as outlined above.


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