Rhynchosia golden mosaic virus

Infected leaves often exhibit significant deformation, including crinkling, curling, or puckering, which drastically reduces the photosynthetic leaf area.

Affected plants show stunted growth with reduced internode length, resulting in a generally dwarfed appearance compared to healthy crops.

Flowering and pod formation are severely impaired, leading to a reduced number of reproductive organs and the development of distorted, malformed pods.

In advanced stages of the infection, leaf tissue may undergo necrosis, followed by premature defoliation and, in severe cases, plant mortality.

The causative agent of the disease is the Rhynchosia golden mosaic virus (RhGMV), classified within the genus Begomovirus, family Geminiviridae.

The virus is characterized by a single-stranded DNA genome encased in twinned (geminate) icosahedral capsids, which is a hallmark of this viral group.

The primary vector responsible for the transmission of RhGMV in field conditions is the tobacco whitefly, Bemisia tabaci.

Transmission occurs in a persistent-circulative manner, meaning the virus must circulate through the vector's body before the insect becomes infectious to healthy plants.

The host range is broad, primarily targeting legumes (Fabaceae), including wild Rhynchosia species that serve as an environmental reservoir for the virus.

The spread of the virus is closely correlated with the population dynamics of the whitefly vector, which thrives in warm and dry environmental conditions.

Temperatures ranging from 25°C to 30°C are optimal for the rapid multiplication of the vector and the subsequent systemic infection of host plants.

Weed populations surrounding agricultural fields often harbour both the virus and the vector, facilitating the movement of the pest into crop areas.

Dense crop planting can create a microclimate that promotes high humidity levels, favouring vector survival and increased rates of viral inoculation.

Lack of proper field sanitation, including the presence of alternate hosts in and around the field, significantly accelerates the epidemic spread of the virus.

Rhynchosia golden mosaic virus causes substantial economic losses by drastically reducing crop yields, sometimes resulting in total crop failure.

Early-season infections are particularly damaging, often preventing the plant from reaching its full potential and ensuring a harvest of poor quality.

The virus impacts the overall vigor of the legume plants, making them more susceptible to opportunistic fungal and bacterial pathogens.

The presence of the virus in seed lots may reduce seed viability and vigor, potentially impacting the quality of subsequent planting materials.

Widespread outbreaks impose quarantine restrictions, limiting the ability of farmers to trade or export agricultural products affected by this virus.

Management focuses primarily on the control of the whitefly vector using a combination of systemic and contact-acting insecticides to reduce population density.

Field sanitation is critical; regular weeding of wild host plants that may act as virus reservoirs is essential to prevent primary infection.

The deployment of host-plant resistance or tolerance through improved crop varieties is the most effective and sustainable strategy for long-term management.

Spatial isolation between new and old crop fields helps minimize the migration of infected vectors from older, virus-positive plant material.

Integrated Pest Management (IPM) practices, including the use of reflective mulches and timely planting schedules, should be employed to reduce vector pressure.