Bean calico mosaic

Pathogen and disease type. Bean calico mosaic disease is caused by the Bean calico mosaic virus (BCMV), a member of the genus Begomovirus in the Geminiviridae family. It is a persistent viral pathogen that causes systemic infection, significantly disrupting the plant's physiological processes and leading to severe stunting and chlorotic leaf patterns.

Host plants. The primary host of this virus is the common bean (Phaseolus vulgaris). It is a major concern in tropical and subtropical regions where the environmental conditions favor the rapid population growth of the vectors that transmit the virus to the fields.

Symptoms and signs. The disease is named after the distinctive chlorotic mosaic pattern on the leaves, which resembles the variegated texture of calico fabric. Infected plants typically exhibit leaf deformation, wrinkling, and severe stunting. The production of pods is significantly reduced, and those that do form are often distorted and of poor market quality.

Conditions for development and spread. The virus is transmitted exclusively by the whitefly species Bemisia tabaci. The insect acquires the virus by feeding on infected plant tissues and subsequently transmits it to healthy plants during further feeding. High temperatures and drought conditions exacerbate the spread, as these factors promote the migration and reproduction of the whitefly population.

Damage and control measures. The economic impact of Bean calico mosaic can be devastating, leading to substantial yield losses in affected bean fields. Effective management strategies involve:

• Utilizing genetically resistant or tolerant bean cultivars.
• Implementing integrated pest management (IPM) to control Bemisia tabaci populations using targeted insecticides.
• Eliminating host weeds that serve as reservoirs for the virus.
• Managing field planting dates to avoid periods of peak whitefly activity.