Rice blast, caused by the Pyricularia oryzae fungus, is a major concern for rice farmers, as it affects various parts of the plant. It begins with lesions on the leaves, often showing elliptical shapes with necrotic borders and an ashy center. Over time, these spots turn into irregular patches with brown borders that weaken the plant. The disease spreads to the leaf collar and culm, which are essential for the plant’s structural integrity. Infection in the culm nodes leads to girdling, weakening the plant’s stem and making it more prone to fall over. he disease also targets the panicle, causing white panicles that indicate a systemic infection. As the infection progresses, the spikelet pedicels become discolored, and the grain development suffers, especially in the milk stage, where grayish brown lesions appear on the grains, leading to poor quality.
Rice Blast Control
The disease is aggravated by external factors such as water deficit, which stresses the plant, and the presence of pests like the yellow stem borer, which weakens the plant and makes it more susceptible to the fungus. The plant’s varieties also play a role in its resistance, with some being more vulnerable to dark brown lesions and poor growth. Nodal infection in the culm and internodal infection further complicate the plant’s condition, especially at the base, where infection can lead to irreversible damage.
Leaf Blast
Leaf blast is one of the most severe manifestations of rice blast, caused by the Pyricularia oryzae fungus. This type of infection typically starts with the formation of lesions on the leaves, which gradually turn into blasted areas. These regions often exhibit a burnt appearance, signaling that the plant is struggling to survive. As the disease progresses, the infection spreads, weakening the leaves and causing them to collapse, leading to lodging. The culm becomes affected, and the plant’s culm nodes start showing signs of weakness. This weakens the plant’s ability to support itself, making it more prone to falling. When this happens during ear emergence, it reduces the plant’s overall potential for proper grain production, and consequently, the crop suffers in quality and yield. The blasted leaves hinder the plant’s ability to photosynthesize, further impacting its growth and resilience.
Neck Blast
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Neck blast affects the neck region of the rice plant, causing significant damage.
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The panicle turns a black color, indicating severe fungal infection.
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The infection leads to the shriveling of the panicle and the inhibition of grain set.
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Grain set becomes incomplete or malformed, reducing the overall quality.
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The neck weakens, causing the panicle to break and hang limply.
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This condition severely affects the final stages of grain development, leading to a dramatic decrease in yield and crop quality.
Node Symptoms
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Pyricularia oryzae fungus causes node symptoms of rice blast.
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The infection leads to black lesions at the basal area and apex of the nodes.
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Infected rice stubble serves as a source of spores, which spread via wind.
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Conidia are translucent, 2-septate, obclavate in shape, and have a tapering structure with a tooth.
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The conidiophores produce clusters of spores that invade through the stoma.
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The fungus damages reproductive structures and darkens the septa of the nodes.
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Node infections weaken the plant, leading to break up and reduced structural integrity.
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Rice seeds may become infected, compromising their quality and development.
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The disease spreads during the growing season, leading to a decrease in yield and plant health.
Identification of Pathogen
The pathogen responsible for rice blast is the Pyricularia oryzae fungus, which can overwinter on infected rice stubble and rice seeds, ready to spread during the next growing season. This fungus produces spores, primarily conidia, that are carried by wind across distances, infecting new rice plants. The conidiophores release these spores in clusters, and they invade the plant through the stoma. These conidia are typically translucent, 2-septate, obclavate, and have a tapering shape with a tooth at the tip. They can range in size, with measurements around µm. As the fungus spreads, it affects the reproductive structures of the rice plant, including the basal area and apex of the nodes, causing the plant to show darkened areas and swollen spots at the point of infection.
The identification of this pathogen involves recognizing the perfect stage of the fungus, where it is in its most active reproductive form. At this stage, conidia extend from the conidiophores, which can be seen in the field as solitary or in clusters. The fungal infection leads to infections that cause visible symptoms on the rice plants, such as darkened lesions that compromise the health of the crop. The spread of the pathogen is significant during periods of wind, as the spores travel, infecting plants across wide distances, affecting yield and quality.
Favourable Conditions
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Blast spores spread easily through the air, traveling long distances.
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Cloudy skies and frequent rain or drizzles provide an ideal environment for the fungus.
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Temperature range of 25-28°C is perfect for Pyricularia oryzae growth.
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High relative humidity and wet leaves promote fungal spread.
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Common in the tropics, particularly in upland rice areas, where these conditions are frequent.
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High nitrogen levels from fertilizers like ammonium sulfate further encourage disease development.
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The combination of these conditions creates an optimal environment for the disease to thrive throughout the year.
Comments on the Disease
Rice blast, also known as rice fever, has been a significant threat to rice-growing countries, with India experiencing major outbreaks as far back as 1918. The disease causes grain loss due to the infection of the plant, particularly through spore germination. As the fungus invades the host tissue, lesion formation begins, leading to sporulation. The conidia produced are highly mobile, dispersed by wind, dew, and free moisture. Spore dispersal depends heavily on favorable conditions, such as high relative humidity and temperature within the temperature range of 25-28°C. These environmental factors promote spore production and infection spread, making susceptible plants more vulnerable to attack.
The infection process is a continual cycle, beginning with inoculum from infected seed or diseased crop residue such as stubble and straw. Moisture and temperature are critical in determining the rate of infection, and in humid conditions, this cycle completes faster. Early infection is often tied to field moisture and favorable moisture levels, while seasonal infection can occur when spores land on plants in rice fields. Infected plants are further compromised by environmental factors that favor fungal growth, like high humidity and warm temperatures, resulting in widespread disease transmission. Managing these growth conditions is essential to reduce the risk of fungal infection and control the disease’s progression.
Management Strategies
Cultural Methods
| Method | Details |
|---|---|
| Resistant Varieties | Use varieties like CO 47, CO 50, ADT 36, ADT 37, ASD 16, ASD 20, ADT 39, ASD 19, TPS 3, White Ponni, ADT 44, BPT 5204, CORH for blast resistance. |
| Tolerant Varieties | Select varieties such as Swarnamukhi, Swathi, Prabhat, IR-64, IR-36, and Jaya for better tolerance against rice blast. |
| Fertilizer Management | Avoid excess N-fertilizer and apply split doses of nitrogen to support plant health without encouraging fungal growth. |
| Weed Control | Manage weed hosts around the field to reduce the chances of fungal spores being spread by weeds. |
| Bund Management | Ensure proper maintenance of bunds to minimize water stagnation and reduce the spread of disease. |
| Fertilizer Application | Apply fertilizers in a balanced manner to promote optimal plant growth and minimize the risk of disease. |
| Crop Management | Incorporate sustainable farming practices to improve crop protection and manage the health of the rice crop throughout the growing season. |
Preventive Methods
| Method | Details |
|---|---|
| Dry Nurseries | Prevents stagnate water, reducing pathogen spread. |
| Late Planting | Avoid late planting to minimize exposure to ideal disease conditions. |
| Burning Straw & Stubbles | Burn straw and stubbles after harvest to eliminate leftover grasses and weeds that harbor pathogens. |
| Seed Treatment | Treat seed with Pseudomonas fluorescens (10g/kg) to reduce fungal infections and promote healthy roots. |
| Water Management | Maintain water depth of 2.5cm and avoid stagnate water for better disease control. |
| Root System Development | Use root soaking techniques for better root system in seedlings, promoting healthy plant growth. |
| Transplanting in Nurseries | Ensure proper nursery care and field management to reduce the risk of disease. |
| Spraying Intervals | Spray P. fluorescens at 0.5% at regular intervals for fungal control and disease suppression. |
| Field Management | Ensure proper water depth, field treatment, and preventive measures to control the spread of rice blast. |
Chemical Methods
| Method | Details |
|---|---|
| Fungicide Selection | Use Captan, Carbendazim, Thiram, and Tricyclazole for seed treatment and fungal control. |
| Lower Doses | Apply lower doses of fungicides to protect seeds, such as 2.0 g/kg for seed protection. |
| Systemic Fungicides | Tricyclazole is a key systemic fungicide for managing rice blast, applied at 1g/lit. |
| Spray Timing | Apply fungicides at 11:00 AM and 3:00 PM, avoiding noon hours for better efficacy. |
| Spraying Intervals | Regular applications, especially during pre-tillering, mid-tillering, and panicle emergence stages. |
| Fungicide Dose for Disease Control | Use Edifenphos (1 ml/lit) and Carbendazim (1.0 gm/lit) for severe disease control. |
| Disease Management | Apply during nursery stage, tillering stage, panicle initiation, and flowering for effective disease suppression. |
| Top Dressing | Apply N fertilizers to support plant health alongside fungicide applications. |
| Disease Control in Stages | Monitor leaf area damage, neck infection, and panicle initiation for effective disease suppression. |
In conclusion, rice blast is a significant threat to rice cultivation, but effective management can be achieved through a combination of cultural, chemical, and preventive methods. By selecting resistant varieties and managing water, fertilizer, and weed control, farmers can create an environment less conducive to the spread of the Pyricularia oryzae fungus. Chemical methods such as the use of systemic fungicides like Tricyclazole and Edifenphos at the correct spraying intervals during critical growth stages, along with seed treatment, further reduce the risk of rice blast. Proper timing of these fungicide applications, coupled with strategic field management and crop protection, helps minimize the impact of this disease, leading to healthier crops, improved yields, and better disease control overall.
FAQS
What is a rice blast?
Rice blast is a devastating disease caused by the fungus Pyricularia oryzae, known for its ability to rapidly spread and cause significant crop losses. This fungus primarily targets the rice plant, particularly the leaf spots, which appear as elliptical, reddish-brown marks along the edges. As the disease progresses, these spots develop into brownish lesions that can weaken the plant. One of the most concerning effects of rice blast is the impact on fruiting panicles, where the infection can lead to neck rot, severely affecting grain production. Additionally, the stunting of plants is another symptom, hindering their overall growth and reducing yield. In my experience, when managing rice crops, it’s crucial to detect early signs of this disease, as it can wreak havoc if left unchecked.
How do you treat rice blast disease?
To manage rice blast, effective treatments include both seed treatment and spraying. For seed treatment, use Captan, Carbendazim, or Thiram at a rate of 2.0 g/kg to reduce fungal infection. Additionally, systemic fungicides like Tricyclazole (1g/lit) and Edifenphos (1 ml/lit) can be applied to the plants, especially during early growth stages. When dealing with established infections, a spraying regimen of Tricyclazole, Carbendazim, or Pyroquilon can significantly aid in controlling the spread. From my experience, timely application of these chemicals is crucial for maintaining crop health.
What chemical is used for rice blast?
For controlling rice blast, pentachlorphenyl acetate is one of the most effective chemicals used. Produced by Kureha Chemical Industries, this chemical targets the disease and helps mitigate its spread. In my experience, its application significantly reduces damage when used at the right time.
Is rice blast caused by fungi?
Yes, rice blast is caused by a filamentous fungus known as Magnaporthe oryzae, which is also a synonym for Pyricularia oryzae. This fungus belongs to the Ascomycota phylum and is responsible for spreading the disease across rice fields. In my experience, understanding the biology of this fungus helps in managing its spread effectively.
What is the best fungicide for rice neck blast?
For controlling rice neck blast, the best systemic fungicides are often based on triazoles and strobilurins. These fungicides, when used judiciously, help to manage the blast effectively. From my experience, combining these fungicides at the right stages of plant growth can significantly reduce the spread of the disease and improve rice yield.