Blast in Rice: Status, Symptoms and Management
Dr. Pramod Kumar Rai1, Dr. Hadi Husain Khan2, Dr. Huma Naz3, Surender Kumar4, Pushpendra Singh Sahu5 & Mohd. Danish6
1Director, ICAR-Directorate of Rapeseed-Mustard Research, Bharatpur – 321303 (Rajasthan), India.
2Research Associate, ICAR-DRMR-APART, Dhubri – 783324 (Assam), India.
3Assistant Professor, Plant Pathology, MANFDC, Hardoi – 241001(U.P.), India.
4Department of Plant Pathology, CSAUA&T, Kanpur – 208002 (U.P.), India.
5Department of Entomology, SHUATS, Naini- Prayagraj (Allahabad) – 211007 (U.P.), India.
6Research Scholar, Department of Entomology, SHUATS, Naini- Prayagraj – 211007 (U.P.), India.
Rice (Oryza sativa L.) is a staple food crop for more than half of the world population which is extensively cultivated in Asia and Africa. Rice is a monocot that is normally grown as crop, although in tropical areas it is perennial. Rice contributes about 117. 47 million tonnes and 46% of total grain production and total cereal production respectively. The status of the rice is increasing at a very fast and continuous pace and it plays a crucial role in food security and energy providence to people. Rice yield and growth is affected by a number of diseases (fungus, virus, bacteria and nematodes) and insect pests (BPH, gall midge, stem borer, rice weevils etc.), among diseases some are significantly cause more damage such rice blast caused by Magnaporthe grisea, sheath blight caused by Rhizactonia solani and Tungro disease by vector Nephotettix spp. The disease was first reported in West Africa (Sierra Leone) in 1930, caused by fungus (Magnaporthe grisea) which forms lesions on leaves, stems, panicles, seeds, and roots also.
Status of Blast in India
Serious yield loss due to blast disease have been recorded in various regions of India, such as Tanjore delta, Nellore, Hyderabad, Mumbai, Orissa, Kashmir and Kerala. The first logged outbreak of blast in 1918 in India, in Tanjore, MacRae estimated the loss as 69% (Thomas and Krishnaswamy, 1948). The damage caused in India due to this disease is as high as 75% in South Eastern India precisely coastal area of Andhra and Odisha. In the last 40 years, rice growing area of both the state has deteriorated around 4.5 million hectares i.e., around 10% of the total rice area of the country. Blast has been severely affecting Uttar Pradesh, Bihar, Delhi, Kolkata, Maharashtra etc.
The fungus that causes blast disease is known as Magnaporthe oryzae (formerly known as Magnaporthe grisea). It is a major concomitant disease in India. It is an ascomycete since it produces ascospores which is sexual spores, structures are called asci, that belong to family Magnaporthaceae. The asci found in specialized structures called perithecia. The mycelium is septate and the nuclei and spores are haploid in nature. They are spread by wind and overwinter survive in seed and debris/stubbles.
Symptoms of Disease
The symptoms include lesions that can be found on all plant parts i.e., leaves, necks, panicles, pedicels, seeds and roots. However, the most common and diagnostic symptom of rice blast is presence of diamond shaped lesions on leaves. Leaf’s symptoms may vary rendering to the environmental conditions, plant age and resistance to host. Lesions initially appear greyish green or brown to dark brown in color and water-soaked with a darker green border which expand to few centimeters while in later stage they become light tan in color with necrotic borders. The collar denotes to the junction of leaf and the stem sheath. The infection on collar consists of necrosis region near joining of the junction. The fungus can produce spores in lesions and in extreme cases the leaf dies and drop. The neck is that portion of the stem that rises above the leaves and ropes the panicle. The nodes are often infected which leads to a condition called rotten neck or neck blast. Neck infections are very critical, causing failure of the seeds to form seeds or triggering the entire panicle to fall over. Panicles are also infected with lesions on branches, spikes, and spikelets. As time passes by, the branches may break at the place lesions. The seeds consist of brown spots and blotches.
Favourable Conditions for Blast
The blast disease is severely high during warm temperatures and high moisture. Generally, rice blast is ideal in moderate temperature (240C) and relative humidity 93%.
Management of Disease
1. Planting of resistant and tolerant varieties (CO 47, CO 50, ADS 16, ADS 20, IR 64, IR 36 etc.).
2. Avoid excesses of nitrogen fertilizers.
3. Removal of weeds and host plant for fungus.
4. Avoid late sowing of the rice.
5. Stubbles and straws should be burnt.
6. Seed treatment should be done with carbendazim, captan, carboxin (2g/kg) of seeds, should be done 24hours before soaking.
7. Seed treatment is also done with Carbendazim or Tricyclazole (2 g/lit) of water for 1 kg of seeds.
8. Seed treatment with talc-based formulation of P. fluorescens (Pf1) @ 10g/kg of seeds, soaked overnight in 1lit of water.
9. Chemical fertilizers: Carbendazim 50WP @ 500g/ha (or), Tricyclazole 75 WP @ 500g/ha, Azoxystrobin 25 SC @ 500 ml/h. Do not apply high doses of any fertilizers.
10. Spraying should be done in morning and noon spraying should be avoided.
Rice blast is a very severe disease in the last few decades and its incidence is increasing continuously which caused a severe loss in the yield and quality of the rice grain. Because of this the management of disease is very important through different management processes like cultural, biological, physical etc. to increase the quality and productivity. Thereby increasing the economic condition of the farmers.
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