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Bean Common Mosaic Virus (BCMV)
BCMV is a seedborne virus transmitted by aphids and mechanically by plant sap. Systemically infected plants, especially those from infected seeds, have leaves with green mosaic patterns and distortions (curling, strapping, or puckering of tissues along leaf veins). Plants may be stunted and have only a few pods, which mature later than uninfected pods. Vascular tissue can become necrotic, producing dark streaks on petioles and stems. Nonsystemic infections can appear as ring-like lesions on foliage. Appearance and severity of symptoms depends on strain of the virus, variety, time of infection, and environmental conditions.
At high temperatures (above 78 F), cultivars with the hypersensitive resistance gene (I gene) respond to necrosis-inducing strains of BCMV with a systemic necrosis called black root. Plants with black root die.
More than 15 strains of BCMV are known, and breeders have incorporated resistance to the more important strains in many commercial varieties. Certified seed programs are restrictive for BCMV contamination. Many types of beans, alfalfa, and common clover are hosts. Controlling large populations of aphids can reduce spread. The primary control is selection of high quality, virus-tested seed of genetically resistant varieties.
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