Sweet potato leaf curl virus

The virus infects the vascular tissue of the host plant. Once systemic infection is established, the virus circulates through the phloem, effectively hijacking the plant's transport system.

It is classified as a persistent, circulative, and non-propagative pathogen in its vector. This means the virus remains in the whitefly for its entire lifespan after acquisition, without replicating inside the insect.

The disease does not move via contact or soil. Instead, the virus is strictly dependent on the Bemisia tabaci whitefly complex for transmission between host plants in the field.

Reservoir hosts, including various wild Ipomoea species, play a critical role in the virus's ecology by providing a constant source of inoculum throughout the year.

The most distinctive symptom is the upward curling of leaf margins, which is often accompanied by significant puckering and crinkling of the leaf surface.

Infected plants may exhibit stunted growth and shortened internodes. Leaves are typically smaller than those of healthy plants and may show interveinal chlorosis, resulting in a mosaic appearance.

The severity of symptoms can be highly variable depending on the specific strain of the virus and the cultivar of the sweet potato being grown. Some cultivars may show mild symptoms while others suffer severe physiological damage.

Visual symptoms often become more pronounced under high temperatures and strong light conditions. In some cases, the leaf veins may become thickened or distorted.

It is essential to distinguish SPLCV symptoms from those caused by nutrient deficiencies or herbicide drift, as the curling and yellowing patterns can occasionally overlap in the field.

Transmission of the virus is exclusively mediated by the whitefly Bemisia tabaci. The prevalence of the disease is directly tied to whitefly population density and activity.

Warm, tropical, and subtropical climates provide optimal conditions for the proliferation of whitefly vectors, leading to a higher incidence of the disease in these regions.

The primary method of long-distance spread is through the movement of infected vegetative cuttings used for propagation. Once a cutting is infected, the virus is present in the entire plant.

The presence of wild morning glory plants around the perimeter of fields acts as a bridge for the virus, allowing whiteflies to pick up the pathogen early in the season.

Dry weather conditions often trigger migrations of whiteflies, which increases the likelihood of virus spread from infested reservoir host plants into commercial sweet potato fields.

SPLCV is a major economic constraint in sweet potato production. The primary damage is a reduction in the size and uniformity of the storage roots, leading to significant yield losses.

Because the virus impairs photosynthesis and nutrient allocation, the storage roots may fail to develop properly, significantly reducing the market value of the crop.

Field studies have indicated that severe infections can result in substantial decreases in total marketable yield, often exceeding 30% depending on the plant growth stage at infection.

The virus also compromises the vigor of the vines, making them more susceptible to drought and other environmental stresses, which further compounds the loss in yield.

Infected planting material creates a cycle of reinfection, forcing farmers to bear additional costs for acquiring certified, disease-free stock to maintain productivity.

The most effective management strategy is the exclusive use of virus-indexed, tissue-cultured plantlets. Starting with clean material is critical for preventing the introduction of the virus.

• Implementing strict whitefly control using integrated pest management (IPM) practices.
• Rogueing and destroying symptomatic plants to reduce the local inoculum source.
• Maintaining a weed-free field, especially focusing on removing wild Ipomoea species.
• Utilizing spatial isolation between new fields and old, potentially infected plantings.
• Monitoring fields regularly for early signs of whitefly colonization.

While developing resistant cultivars is a high priority for researchers, it remains challenging due to the emergence of new viral variants, making cultural control essential for the time being.