Ascochyta Blight in Beans

Ascochyta Blight leaf and pod spot is an important disease of beans. Symptoms occur on leaves, stems and pods of infected plants, and can be confused with the early stages of chocolate spot. On leaves, small, circular, dark-brown spots appear first. As the disease develops, lesions enlarge and turn light and then change to dark grey in colour. They become irregular in shape, often zonate, and may coalesce to cover most of the leaf surface. Leaf tissue next to the lesions may become black and necrotic. Within the lesions, numerous pinhead- sized black fruiting bodies (pycnidia) of the fungus develop. These appear only under moist conditions and are often concentrically arranged. On the stem, lesions are more elongated, sunken and darker than leaf lesions and are usually covered with scattered pycnidia. Stems may split and break at the point of infection causing plants to lodge. On pods, lesions are sunken and have pale centre and dark margins; they can be covered by numerous pycnidia. Well developed lesions can penetrate the pod and infect developing seeds causing them to be shrunken and discoloured. Badly infected seeds have yellowish brown stains on the outer seed coat, which considerably reduces its market value.