Anthracnose of Beans
Bean anthracnose, caused by the fungus Colletotrichum lindemuthianum, is a major disease of beans (Phaseolus vulgaris L.), causing serious crop loss in many parts of the world.
Seedlings grown from infected seeds often have dark brown to black sunken lesions on the cotyledons and stems. Severely infected cotyledons senesce prematurely, and growth of the plants is stunted. Diseased areas may girdle the stem and kill the seedling.
Under moist conditions, small, pink masses of spores are produced in the lesions. Spores produced on cotyledon and stem lesions may spread to the leaves. Symptoms generally occur on the underside of the leaves as linear, dark brick-red to black lesions on the leaf veins. As the disease progresses, the discoloration appears on the upper leaf surface. Leaf symptoms often are not obvious and may be overlooked when examining bean fields.
The most striking symptoms develop on the pods. Small, reddish brown to black blemishes and distinct circular, reddish brown lesions are typical symptoms. Mature lesions are surrounded by a circular, reddish brown to black border with a grayish black interior. During moist periods, the interior of the lesion may exude pink masses of spores. Severely infected pods may shrivel, and the seeds they carry are usually infected. Infected seeds have brown to black blemishes and sunken lesions