Leaf twister disease of onion (Allium cepa L.)

Leaf twister disease of onion (Allium cepa L.)

1996/1997

A:PS

Onion (Aliium cepa L.) is one of the important cash crops grown in Sri Lanka. A disorder called "Leaf twister disease" has gained importance recently specially on onion crops grown during the Maha season. A severe outbreak of the disease was observed in both bulb crop and seed crop at Field Crops Research and Development Institute, Maha Illuppallama during the 1995/96 Maha season. The characteristic symptoms of the disease are leaf curling, twisting and chlorosis and abnormal elongation of the pseudostem followed by bulb rotting. Lesions with black, minute, slightly raised acervuli (fruiting bodies) with pink masses of conidia could be seen scattered on leaves and flower stalks. Isolations were made from infected leaves and flower stalks and the pathogen was identified as a fungus, Colletotrichum gloeasporioides (Penz.) Sacc. ( the perfect stage of Glomerella cingulata (Stonem) Spauld. & Schrenck), and its pathogenicity was confirmed. High relative humidity (85 - 96 %), moderate temperature (20 - 31~C) and cloudy rainy weather are the factors that favour the development and spread of the disease. Spores of the fungus can spread through soil, water, seed and crop debris. Crop sanitation including the destruction of crop debris will reduce the infection; use of healthy seeds and planting material is important to control the disease.

v.151:25-33, TROPICAL AGRICULTURIST: AGRICULTURAL JOURNAL OF SRI LANKA

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