ABSTRACT
Symptoms and diagnostic features Symptoms consist of leaf chlorosis and mottling, downward cupping of leaves, and some reduction in leaflet size (340, 341). Seedborne infection can result in young plants having a leaf mosaic of light and dark green areas, with paler sections near the leaf margin. The first true leaf shows dark green blistering. Aphidborne infection on older plants produces crinkled, chlorotic leaves with a stiff appearance, but does not cause the mottling or downward rolling of the leaf margin associated with seedborne infection. The rolling symptom is useful in distinguishing BCMV from Bean yellow mosaic virus. Symptoms tend to become less pronounced as the season progresses. Severe stunting and black root symptoms are produced at temperatures of 20º C or greater with virulent strains, and at higher temperatures (30º C) with less severe strains. Local vein necrosis occurs as a hypersensitive reaction in some resistant cultivars and this provides field resistance.
