Colletotrichum gloeosporioides, the Causal Agent of Onion Twister Disease

Abstract

Onion twister is serious rainy season disease of several kinds of Allium spp. in Thailand. The disease is characterised by curling, twisting and chlorosis of the leaves; the plants are stunted and the bulbs elongated, undeveloped and often unsuitable for harvesting. Some diseased plants rot before harvest, while others rapidly decay when stored. Anthracnose is often found on different components of diseased plants.
Acervuli of Colletotrichum gloeosporioides Penz were isolated from components of diseased plants. Inoculation tests satisfied Koch’ postulates and demonstrated for the first time that this fungus is the causal agent of onion twister disease. It is considered possible that onion twister disease and onion anthracnose two phases of the same disease.