Sweet potato leaf curl virus

Chlorosis is frequently observed, where the tissue between the veins turns yellow while the veins themselves remain green. In some sensitive cultivars, this condition may lead to mottled or mosaic patterns, making the leaves look variegated and unhealthy.

Infected plants exhibit stunted growth and an overall reduction in vigor. The internodes are often shortened, leading to a compact, bushy habit. This restricted growth pattern prevents the plant from developing sufficient biomass to support proper tuber expansion.

Symptoms are not uniform across all varieties and can vary significantly depending on the environmental conditions, such as temperature and water availability. Often, the youngest leaves near the growing tip show the most prominent symptoms at the beginning of the infection.

Since these visual cues can be misleading and may resemble symptoms caused by other pathogens or nutritional deficiencies, accurate diagnosis requires molecular techniques such as PCR to detect the specific viral RNA within the leaf tissue.

The causal agent is the Sweet potato leaf curl virus, which belongs to the genus Polerovirus. This virus is a specialized plant pathogen characterized by its reliance on insect vectors for dissemination among hosts.

The virus consists of single-stranded RNA particles. It is transmitted in a persistent, circulative manner, meaning the insect vector must feed on an infected plant to acquire the virus, which then moves through the insect's hemolymph to its salivary glands before transmission to a new host.

Because the virus is not mechanically transmitted (e.g., via farm equipment or handling), its movement is exclusively linked to the feeding habits of its vectors, primarily aphids. This biological constraint is crucial for implementing targeted control programs.

The host range of SPLSV is largely limited to the Convolvulaceae family. Sweet potato (Ipomoea batatas) is the most economically significant host, serving as the primary reservoir in commercial agricultural settings.

The ability of the virus to persist in vegetative propagules, such as storage roots and vines, allows it to survive between seasons, facilitating its spread across different regions when infected material is moved and planted.

The spread of the virus is highly dependent on the population dynamics of its insect vectors. Warm and dry weather conditions are generally favorable for the rapid multiplication and migration of aphids, increasing the likelihood of widespread infection in the field.

The most significant risk factor for the introduction of the virus into a new area is the use of infected planting material. Once the virus is established in a field, the local insect population facilitates its rapid transmission throughout the entire plantation.

Weed management plays a pivotal role, as various wild species of the Convolvulaceae family serve as reservoirs. These weeds can harbor the virus even when the sweet potato crop is not present, ensuring the presence of the pathogen in the landscape.

Agronomic practices, including high planting density and poor weed control, create a microclimate that supports larger vector populations. Consequently, fields that are not properly managed or monitored are at a much higher risk of experiencing severe virus outbreaks.

Geographical distribution is linked to the presence of compatible vector species. In tropical environments where both the host plant and the vectors are active throughout the year, the disease pressure is constant and requires year-round management strategies.

The primary economic impact of SPLSV is a significant reduction in tuber yield. Infected plants often produce fewer and smaller storage roots, which fail to reach the quality standards required for the fresh market or processing industry.

The virus disrupts the plant's metabolic processes, affecting the accumulation of starches and sugars in the tubers. This reduction in quality diminishes the nutritional value and can negatively affect the taste and texture of the harvested sweet potatoes.

Early-stage infection can lead to near-total loss of the marketable crop. Furthermore, the persistent nature of the infection means that once a crop is infected, the tubers or cuttings derived from it are largely unsuitable for future planting, leading to a loss of valuable germplasm.

Farmers face increased production costs due to the need for continuous monitoring, the application of insecticides to control vectors, and the frequent requirement to purchase certified, disease-free planting material to replace degenerated stocks.

Overall, the virus limits the profitability of sweet potato production, often forcing growers to adopt more intensive and expensive management practices to mitigate the damage and maintain consistent yields across successive seasons.

The foundation of effective management is the exclusive use of virus-free, certified planting material. Propagation via tissue culture (meristem tip culture) is the gold standard for ensuring that new plantings start free of the virus.

Regular surveillance and the prompt roguing (removal and destruction) of symptomatic plants are essential to reduce the viral load within the field. This prevents the vectors from picking up the virus from infected plants and spreading it further.

Implementing a strict vector control program is necessary. The use of systemic or contact insecticides during the early growth stages of the crop can significantly reduce the initial infection rate by controlling the aphid population.

Maintaining a clean field environment by eliminating reservoir weeds in the vicinity of the plantation helps to interrupt the virus's life cycle. Spatial isolation between new and old sweet potato patches is also recommended.

• Planting certified disease-free material.
• Monitoring and managing aphid populations.
• Promptly removing and destroying symptomatic plants.
• Controlling wild weeds of the Convolvulaceae family.
• Applying spatial isolation between planting sites.