In this article we will discuss about:- 1. Worldwide Occurrence of Banded Leaf and Sheath Blight 2. Economic Importance and Epiphytotics of Banded Leaf and Sheath Blight 3. Symptomatology 4. Causal Organism.
Worldwide Occurrence of Banded Leaf and Sheath Blight (BLSB):
The Banded leaf and sheath blight (BLSB) of maize was first reported from Sri Lanka. Since then, the occurrence of the disease has been recorded in Sierra Leone, Phillippines, Ivory Coast, Malaysia, Japan, Bhutan, Burma, Indonesia Nepal, Pakistan, Southern China and Vietnam and Arkansas, U.S.A. BLSB is one of the important diseases of maize in south and Southeast Asia.
In India, the occurrence of this disease was first recorded by Ullstrup in the Tarai region of Uttarakhand (Previously U.P.) Now it is known to be present in the states of Himachal Pradesh, Uttar Pradesh, Haryana, Punjab, Madhya Pradesh, Rajasthan, West Bengal, Meghalaya, Bihar and Jharkhand. It develops along the entire lengths of the Himalayas at altitudes between 1,100 to 1,500 meters above sea level.
Since the first report of occurrence of the disease in India, it has been regarded as minor disease, although its widespread occurrence was observed in different parts of Himachal Pradesh, particularly in Mandi district. Due to the epidemic, commonly cultivated maize hybrid him-123, suffered a serious loss in grain yield. Now the disease has an alarming situation in different parts of the country.
Bertus (1927) first described the disease as sclerotial disease of maize. Since then it has been described under various names like banded sheath rot, banded sclerotial disease, ear rot, Sheath blight, Horizontal banded blight.
Economic Importance and Epiphytotics of Banded Leaf and Sheath Blight (BLSB):
Singh and Sharma (1976) recorded a loss in grain yield ranging from 11.8 to 40.5 per cent with an average of 19.8 per cent in ten maize cultivars. However, the ear rot phase of the disease resulted in greater loss in grain yield.
Lai (1980) reported the reduction in grain yield within a range of 23.9 to 31.9 per cent in ten maize cultivars depending upon the disease severity levels ranging from 69.9 to 87.3 per cent, but when ear rot phase predominates losses in yield can go up to 100 per cent.
Lai (1985) reported that the grain yield loss could go up to 97.4 per cent. Payak and Sharma (1985) reported that annually around 1.0 per cent of the total grain yield is reduced by BLSB in India. The banded leaf and sheath blight of maize caused by R. solani f. sp. sasakii has become economically important not only in India but also in the whole of tropical Asia.
The widespread occurrence of the disease was observed in different parts of Himachal Pradesh, Particularly in Mandi district. Ahigh incidence of this disease was observed in Jhabol and other hilly region of Udaipur district of Rajasthan.
Survey during kharif, 2005 and 2006 were carried out to record occurrence of disease which revealed that banded leaf and sheath blight incited by Rhizoctonia solani, is wide spread with the disease severity ranging from 30.30 to 80.46 per cent and gaining the economic importance in and around Ranchi, Jharkhand.
Symptomatology of Banded Leaf and Sheath Blight (BLSB):
Bertus (1927) recorded the disease symptoms on leaf sheath as small purplish brown lesions or greenish olive brown large continuous patches; on stalks immediately below the diseased leaf sheath and on the stem at the base of female inflorescence as pale olive brown lesions.
The author also reported the presence of sclerotia on diseased plants and restricted development of flowers, withering and outright death of the diseased plants.
Other workers have observed similar symptoms also. However, Reyes (1941) and Payak and Renfro (1966) could trace the symptoms on drooping leaves in contact with soil. Von Eijnatten (1961) found the disease symptoms on leaves, sheaths, ear husk and ears whereas, Wiltshire (1956) and Heath (1956) observed it on lower sheaths only. The disease is also manifested as rotting of ears.
Ahuja and Payak (1982) documented in-depth symptoms and signs of the disease that included some rarely observed ones apart from the characteristics banded lesions on leaves and sheaths.
Such symptoms included stalk lesions or rind spotting, stalk breakage, clumping and caking of style horse shoe shaped lesions with banding on ear ropes which is considered most important for diagnosis of the disease in pathological tests.
If seed, as kernel rots incited by other fungi, do not produce such blemishes in field or during storage signs appeared in the form of running hyphae on unaffected parts of leaves, sheaths and adaxial and abaxial surface of ear husks.
Hirel (1988) observed the symptoms as reddish eye spot lesions with dark red to purple margin on stalks near the soil line. Prolific sclerotial and hyphal development was also recorded on older sheaths, which appeared as yellow green discoloration with a thin black border. However, in India, such symptoms have not been observed.
Causal Organism of Banded Leaf and Sheath Blight (BLSB):
The anamorphic stage of the pathogen causing banded leaf and sheath blight of maize is Rhizoctonia solani Kuhn f. sp. sasakii. However, in literature different workers have described it under various names. Bertus (1927) identified the fungus causing sclerotial disease of maize as R. solani Kuhn.
Since then, it has been described under the names of R. solani state of Corticium solani (Prill and Delacor), Costan and Dufour, Corticium vagum Berki and Curt.
Hypochnus sasakii Shirai, Pellicularia sasakii (Shirai) Ito, Corticium sasakii (Shirai) Matsumoto. Such multiplicity in names has resulted due to occurrence of the pathogen more frequently in anamorphic stage and availability of few characters for differentiation of teleomorphic stage.
A similar type of complex nomenclature is met with rice sheath blight pathogen, originally described from Japan as Hypochnus sasakii shirai. However, the fungus has most frequently been referred to as Corticium sasakii (Shirai) Matsumoto.
Rice and maize sheath blight pathogens are identical as evidenced by positive cross inoculation of two isolates, production of similar symptoms on different host plants, similar sclerotial and mycelial characters, nuclear number and similar response in temperature, in-vitro host-parasitic interaction in relation to disease development, similar disease index and similarity in anastomosis behaviour.