Incidence
Bean common mosaic virus (BCMV) has been found wherever dry edible beans are grown in the province. In some years, the disease can be severe in individual fields.
Appearance
Infection of dry edible beans with the virus can cause various symptoms. Leaves of infected plants have a mosaic of light yellow-green and dark green patches that are puckered. The leaves curl downward along the margin, or may be otherwise malformed. Plants are stunted and if infection occurs early, they may flower but not produce seed.
Another symptom referred to as “black root reaction” is displayed in varieties containing a specific gene (dominant resistant gene I). These varieties are resistant to all strains of bean common mosaic virus except when plants growing at high temperatures react to the virus (hypersensitive response), causing the “black root reaction.” The result is a browning or blackening of the vascular tissue inside the stem, followed by wilting and plant death. The obvious symptom of “black root reaction” is the discolouration or streaking of the outer stem (water conducting tissue), which produces a black or brown outer streaking of the stem from the soil line up. This blackening may only be visible on one side of the stem.
Disease Cycle
BCMV is in the potyvirus group. The virus is primarily spread from field to field through infected seed. Aphids can then spread the virus within the field. Severe losses occur when susceptible varieties are infected early either through infected seed or from being close to other infected plants or fields that have high aphid populations. There are several strains of the virus — strain 1 is the predominant one in Ontario.
Management Strategies
Do not plant seeds harvested from diseased plants. Avoid damaging the plants during cultivation.
To mitigate incidence of the disease, select resistant varieties. To determine if a variety is resistant to BCMV, consult the Variety Trial Reports posted at www.gobeans.ca.
