SHEATH BLIGHT OF RICE | Lecture notes Agronomy

Volume 05 - Issue 07 - July 2023 268 | P a g e

Sheath Blight Disease of Rice and their Management

Article ID: 43088

Dr. Anupam Kumar1, Shivani Chaudhry2

1(Assistant Professor), Department of Plant Pathology, School of Agriculture, Abhilashi University,

Mandi H.P.175028 (India).

2Ph.D. (Research Scholar), Plant Pathology, SVPUA&T Meerut UP 250110 (India).

Rice is affected by a series of epidemics as well as devastating diseases. Rice Sheath Blight is one of the

detrimental diseases of rice. Rice sheath blight disease caused by R. solani is a destructive disease that

leads to massive yield loss and degradation of rice. This disease was first reported by Miyake from Japan

in 1910 referred as ‘Oriental leaf and sheath blight’. Although from India, it was first reported by Pancer

and Chahal in 1963. Apropos of Lee and Rush (1983) yield loss occurs between 20 to 50% when all the

sheaths are infected. According to Roy (1979), it was estimated that there was yield loss of 10 to 36% in

Assam depending on the growth stage of the plant when the fungus attacks. Sheath blight occurs in areas

having high temperature and high humidity content and by application of excess nitrogenous fertilizer.

However, there is no commercial variety which is resistant to this disease, but the land races can be used

to achieve the novel genes for disease resistance as well as abiotic stress tolerance and source of yield

enhancing traits. Rice Sheath Blight disease management is difficult because of high genetic diversity of

the causal organism and wide host range. Apart from the conventional breeding approaches and application

of hazardous pesticides. In spite of successful adaptation of scientific developments and establishment of

rice crops, pests and pathogens are inevitable and protective methods should be available to minimize

the crop loss.

Pathogen: Rhizoctonia solani (Teleomorph: Thanatephorus cucumeris)

Distribution: Its occurrence was recorded throughout the temperate and tropical rice growing areas

including Africa, Bangladesh, Brazil, Burma, Colombia, China, Cuba, Germany, Fiji, Formosa, India,

Indonesia, Iran, Korea, Liberia, Madagascar, Malaya, Malaysia, Netherland, Nigeria, Papua New Guinea,

Philippines, Russia, Senegal, Sri Lanka, Surinam, Taiwan, Thailand, Trinidad, Tobago, UK, USA,

Venezuela and Vietnam. In India sheath blight, first reported from Gurdaspur by Paracer and Chahal

(1963), has become a major production constraint in Punjab, Haryana, eastern Uttar Pradesh,

Uttarakhand, Bihar, West Bengal, Odisha, Chhattisgarh, Andhra Pradesh, Tamil Nadu, Karnataka,

Kerala, Jammu and Kashmir, Madhya Pradesh, Assam, Manipur and Tripura (DRR, 2006-2010) due to

wide spread cultivation of high yielding rice varieties with a narrow genetic base, heavy dependency on

chemical fertilizers and apparent change in climate.

Hosts: Rice, bean, soybean, sugarcane, sorghum, corn, turfgrass, and weed hosts such as barnyard grass,

crabgrass, and broad leaf signal grass.

Symptoms: Sheath blight is characterized by large oval spots on the leaf sheaths and irregular spots on

leaf blades. Infections usually begin during the late tillering-joint elongation stages of growth. Lesions

about 0.5 - 1 cm in width and 1 - 3 cm in length are formed a little above the waterline on infected culms.

Fungus mycelium grows up the leaf sheath, forms infection structures, infects and causes new lesions. The

infection can spread to leaf blades. The lower leaf sheaths and blades are affected during the jointing stages

of growth. After the panicle emerges from the boot, the disease progresses rapidly to the flag leaf on

susceptible varieties. With very susceptible varieties, the fungus will spread into the culm from early

sheath infections. Infected culms are weakened, and the tillers may lodge or collapse. The lesions have

grayish-white or light green centers with a brown or reddish-brown margin. As lesions coalesce on the

sheath, the blades turn yellow-orange and eventually die. As areas in the field with dead tillers and plants

increase, they may coalesce with other affected areas to cause large areas of lodged, dead and dying plants.

Damage is usually most common where wind-blown, floating debris accumulates in the corners of cuts

when seedbeds are prepared in the water. Sheath blight also affects many grasses and weeds other than

rice, causing similar symptoms. Sclerotia that survive between crops are formed on the surface of lesions

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Sheath Blight Disease of Rice and their Management

Article ID: 43088

Dr. Anupam Kumar^1 , Shivani Chaudhry^2 (^1) (Assistant Professor), Department of Plant Pathology, School of Agriculture, Abhilashi University, Mandi H.P.175028 (India). (^2) Ph.D. (Research Scholar), Plant Pathology, SVPUA&T Meerut UP 250110 (India). Rice is affected by a series of epidemics as well as devastating diseases. Rice Sheath Blight is one of the detrimental diseases of rice. Rice sheath blight disease caused by R. solani is a destructive disease that leads to massive yield loss and degradation of rice. This disease was first reported by Miyake from Japan in 1910 referred as ‘Oriental leaf and sheath blight’. Although from India, it was first reported by Pancer and Chahal in 1963. Apropos of Lee and Rush (1983) yield loss occurs between 20 to 50% when all the sheaths are infected. According to Roy (1979), it was estimated that there was yield loss of 10 to 36% in Assam depending on the growth stage of the plant when the fungus attacks. Sheath blight occurs in areas having high temperature and high humidity content and by application of excess nitrogenous fertilizer. However, there is no commercial variety which is resistant to this disease, but the land races can be used to achieve the novel genes for disease resistance as well as abiotic stress tolerance and source of yield enhancing traits. Rice Sheath Blight disease management is difficult because of high genetic diversity of the causal organism and wide host range. Apart from the conventional breeding approaches and application of hazardous pesticides. In spite of successful adaptation of scientific developments and establishment of rice crops, pests and pathogens are inevitable and protective methods should be available to minimize the crop loss. Pathogen: Rhizoctonia solani (Teleomorph: Thanatephorus cucumeris ) Distribution: Its occurrence was recorded throughout the temperate and tropical rice growing areas including Africa, Bangladesh, Brazil, Burma, Colombia, China, Cuba, Germany, Fiji, Formosa, India, Indonesia, Iran, Korea, Liberia, Madagascar, Malaya, Malaysia, Netherland, Nigeria, Papua New Guinea, Philippines, Russia, Senegal, Sri Lanka, Surinam, Taiwan, Thailand, Trinidad, Tobago, UK, USA, Venezuela and Vietnam. In India sheath blight, first reported from Gurdaspur by Paracer and Chahal (1963), has become a major production constraint in Punjab, Haryana, eastern Uttar Pradesh, Uttarakhand, Bihar, West Bengal, Odisha, Chhattisgarh, Andhra Pradesh, Tamil Nadu, Karnataka, Kerala, Jammu and Kashmir, Madhya Pradesh, Assam, Manipur and Tripura (DRR, 2006-2010) due to wide spread cultivation of high yielding rice varieties with a narrow genetic base, heavy dependency on chemical fertilizers and apparent change in climate. Hosts: Rice, bean, soybean, sugarcane, sorghum, corn, turfgrass, and weed hosts such as barnyard grass, crabgrass, and broad leaf signal grass. Symptoms: Sheath blight is characterized by large oval spots on the leaf sheaths and irregular spots on leaf blades. Infections usually begin during the late tillering-joint elongation stages of growth. Lesions about 0.5 - 1 cm in width and 1 - 3 cm in length are formed a little above the waterline on infected culms. Fungus mycelium grows up the leaf sheath, forms infection structures, infects and causes new lesions. The infection can spread to leaf blades. The lower leaf sheaths and blades are affected during the jointing stages of growth. After the panicle emerges from the boot, the disease progresses rapidly to the flag leaf on susceptible varieties. With very susceptible varieties, the fungus will spread into the culm from early sheath infections. Infected culms are weakened, and the tillers may lodge or collapse. The lesions have grayish-white or light green centers with a brown or reddish-brown margin. As lesions coalesce on the sheath, the blades turn yellow-orange and eventually die. As areas in the field with dead tillers and plants increase, they may coalesce with other affected areas to cause large areas of lodged, dead and dying plants. Damage is usually most common where wind-blown, floating debris accumulates in the corners of cuts when seedbeds are prepared in the water. Sheath blight also affects many grasses and weeds other than rice, causing similar symptoms. Sclerotia that survive between crops are formed on the surface of lesions

on these weed grasses, as well as on rice and soybeans. The sclerotia are tightly woven masses of fungal mycelium covered by an impervious, hydrophobic coating secreted by the fungus. A. Symptoms of Sheath blight B. Hyphae of Sheath blight

Biology

Rhizoctonia solani produces thread-like growth called hypha (plural, hyphae); large masses of hyphae are referred to as mycelium. The hyphae of Rhizoctonia solani have the following characteristics: Some shade of brown. A special type of cross wall within the hyphae, called a dolipore septum. Each cell is multinucleate (has many nuclei) rather than binucleate. Branches that are produced at right angles. No asexual spores are formed by the mycelium. Favorable Conditions for Rhizoctonia : Hot temperatures (70- 90 °F or 12- 32 °C) favor the growth of Rhizoctonia , so it is more problematic in late spring and summer. Rhizoctonia does not require free water for its lifecycle, so it prefers even, moderate moisture in the growing medium, not wet, saturated conditions. Because it tends to dwell near the growing medium surface, it prefers high humidity as with all fungal pathogens. When humidity is high, brown webbing can be seen in the affected parts of the plant. Frequent misting, close spacing of plants, wet leaves / stems and lack of airflow all favor Rhizoctonia development. Therefore, it is a common problem with cuttings and young plants. Plant susceptibility greatly increases if there are open wounds on plant parts near the soil line. These wounds serve as entry points for Rhizoctonia. Disease cycle: Although basidiospores produced by Thanatephorus cucumeris on host plant can initiate infection, it is generally considered unimportant in the epidemiology of rice sheath blight. The pathogen survives through sclerotia and mycelia in infected plant debris/straw and through weed hosts in tropical environments while in temperate regions, the primary source of inoculum is sclerotia. In double cropped areas, the fungus perpetuated through ratoons acting as a source of primary inoculum. Agricultural operations such as ploughing, leveling, transplanting, and weeding help the surviving sclerotia to come to the water surface and make the initial contacts with the host. Rainwater runoff and flood irrigation permit good dispersal of floating sclerotia and consequently provide the primary foci of infection. Disease management: a. Avoid excess dose application of fertilizers. b. Remove diseased plants and plant residues from the growing area. c. Increase plant spacing to allow humidity to escape the plant canopy and try to maintain humidity levels below 93%. d. Seed treatment with Pseudomonas fluorescens @ of 10g/kg of seed followed by seedling dip @ of 2.5 kg or products/ha dissolved in 100 litres and dipping for 30 minutes.

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