Rice (Scientific name: Oryza sativa) also known as the “King of Cereals” is consumed as a staple source of dietary food by over one-third of the world’s population. Rice being a tropical crop, flourishes well in hot and humid climate and can be grown both in irrigated and rainfed areas where there is assured rainfall annually, hence it can be grown in kharif as well as rabi seasons. In Nagaland, rice is the staple food of the people which occupies almost two-thirds of the total cultivable land and contributes more than 80 percent of the total food production in the state. Rice is mainly cultivated under two farming situations namely, jhum/shifting cultivation (rainfed/upland) and wet rice cultivation/terrace rice cultivation (irrigated). Jhum rice is grown in almost all parts of the state whereas terrace rice is mainly grown in the districts of Dimapur, Kohima, Peren, Phek and Wokha. The total area under rice cultivation is 2,11,130 ha with a production of about 5,54,669 mt (Nagaland Statistical Handbook, 2023). Some of the indigenous varieties of rice grown in Nagaland are Sinsatsu, Henigido, Akatan, Kemenhya, Ngoba, Mikotchuwakelu, Sarang, Moyatsuk, Mamen, Nagaland special etc (Rice Resource Book Nagaland, 2007).In the fields, rice plant encounters several fungal diseases which can become devastating during heavy rainfall. Generally, rice is affected by 36 fungal diseases, 21 viral and 6 bacterial diseases reported so far. Presently, there are two important fungal rice diseases which have been reported and is prevalent in Nagaland and are discussed below.
TWO MAJOR DISEASES OF RICE IN NAGALAND:
1. BLAST OF RICE/ RICE BLAST: (causal organism: Magnaporthe grisea)-a fungi: Blast disease of Rice is one of the most destructive diseases of rice which can cause an average grain loss of about 70-80 percent. The disease is primarily spread through infected seeds, rice stubbles, wind and water.
How to Identify Blast of Rice Disease:
• Initial symptoms appear as white to gray-green lesions or spots, with dark green borders.
• Older lesions on the leaves are elliptical or spindle-shaped and whitish to gray centers with red to brownish or necrotic border.
• Some spots on the leaf resemble diamond shape, wide in the center and pointed toward either ends.
• Lesions (spots) can enlarge and coalesce, growing together, to kill the entire leaves.
The disease attacks the leaves, nodes, collars and panicles of a rice plant. Rice grown in upland and higher elevation having water scarcity are prone to the disease while drought like situation growth makes the paddy vulnerable to disease attacks.
Conditions that Favour the Spread of the Disease
• High humidity (above 90%), prolonged leaf wetness (over 10 hours), temperature between 20-30ºC and excessive nitrogen (Urea) fertilization.
Example: On 26th July, 2021, a total of 955.5 hectares of jhum area in nine villages—located in Naginimora subdivision of Mon district, were affected by Rice blast. The infestation rate was 80-90 percent and about 1,034 farming households were affected by the disease outbreak as reported by State Department of Agriculture, Nagaland in Morung express.
2. SHEATH ROT OF RICE: (Causal organism: Sarocladium oryzae)-a fungi: In various regions around the world depending upon the weather conditions during the crop growth, there have been reports of severe losses reaching as high as 70-85%. Sheath rot infects the rice plant at all growth stages, but it is most destructive when infection occurs during or after the booting stage, before the emergence of the panicle. The pathogen persists in plant residues (straw and stubbles), diseases seeds and soil. Secondary infection occurs mainly by air borne conidia.
How to Identify the Sheath Rot Disease:
• The typical sheath rot lesion starts at the uppermost leaf sheath enclosing the young panicles. It appears oblong or as irregular spot with dark reddish, brown margins, and gray center or brownish gray throughout.
• Affected leaf sheaths may have abundant whitish powdery fungal growth (mycelium) visible on the outer surface.
Conditions that Favour the Spread of Disease:
• High amount of nitrogen (Urea), high relative humidity, and dense crop growth favours sheath rot development. The fungus grows best at 20 to 28°C.
Example: In 2011, a press release published in the local daily, Nagaland Post issued by then Deputy Project Director Rosalane Kithan informed that more than 80% of Jhum fields were affected by particular rice disease ‘sheath’ rot caused by fungi Sarocladium oryzae in the previous crop season at Teichüma village which was conducted by ATMA in collaboration with NU: SASRD Medziphema.
MANAGEMENT OF BLAST AND SHEATH ROT OF RICE:
1. Use of healthy and seeds which are free from diseases free.
2. Ensure proper disposal of rice stubbles (stubbles- the remaining portion of the rice plant, including straw and crown left in the soil surface after harvesting).
3. Crop rotation of Rice with other crops (soybeans, mungbean, mustard etc.) helps break the disease cycle and its spread in the coming cropping season.
4. Regular monitoring of rice fields for development of any disease symptoms in order to manage it.
5. Adjust planting time by sowing the seeds early when it is possible, usually after the onset of rainy season helps in the management of rice blast.
6. Seed treatment with Trichoderma (fungi) or Bacillus subtilis(bacteria)@ of 10g/kg of seed dissolved in 100 litres and dipping for 30 minutes helps in managing both blast and sheath rotdisease.
7. Soil application of P.fluorescens @ of 2.5 kg/ha after 30 days of transplanting for both the diseases.
8. Systemic fungicides like Triazoles and Strobilurins are to be used as a last resort in recommended dosage for managingrice blast.
Article contributed by Kavi Sumi1, Akumla Longchar1, Virosanuo Solo1, Lowrence Kithan1, Bendangsenla2, and E. Lireni Kikon2 (1ICAR-AICRP on Kharif Pulses & ICAR-AICRP on Linseed, SAS: NU & 2Department of Plant Pathology, SAS:NU)
