Sweet potato feathery mottle virus

SPFMV is considered the most widespread and economically significant virus affecting sweet potato crops globally. It frequently occurs in co-infection with other viruses, which often leads to severe plant stress.

The transmission of this virus is non-persistent. This means that aphid vectors can acquire the virus by feeding on infected plants for a very short period and immediately transmit it to healthy plants.

The virus is primarily carried over from season to season in infected vegetative propagation material, such as vine cuttings or storage roots used for sprouting.

Due to the high mutation rate of the virus, there are several distinct strains that vary in their geographic distribution and the severity of symptoms they induce in different sweet potato cultivars.

The characteristic symptom is the development of chlorotic spots or feather-like patterns on the leaves, which gives the disease its common name. These patterns are most clearly visible on young, actively growing leaves.

In some cases, infected plants may show vein clearing, purple ring spots, or necrotic vein banding. It is important to note that many tolerant cultivars show no visible symptoms while still harboring the virus.

Storage roots may develop an internal condition known as "internal cork," characterized by hard, brown, corky tissue within the flesh. This significantly degrades the culinary quality of the produce.

Chronic infection often leads to stunted growth, reduced leaf size, and general physiological decline of the plant, which is usually reflected in lower tuber yield.

• Feather-like chlorotic leaf patterns
• Vein clearing and necrotic banding
• Internal cork formation in storage roots
• Overall plant stunting and reduced vigor

The spread of SPFMV in the field is largely dependent on aphid populations. Various species of aphids serve as the primary vectors that carry the virus from infected reservoirs to healthy crops.

Environmental conditions that favor the rapid proliferation of aphid populations, such as moderate temperatures and high humidity, significantly accelerate the spread of the virus within a planting.

The primary source of the virus is infected planting material. Once the virus enters the field via contaminated stock, it can spread quickly if vectors are present.

Weedy borders and proximity to older sweet potato patches act as secondary reservoirs for both the virus and its aphid vectors, increasing the risk of infection.

Lack of rigorous phytosanitary standards during the selection of planting material leads to the accumulation of the virus over several growing cycles, ultimately leading to yield degeneration.

The economic impact of SPFMV is primarily due to reduced tuber yield. Because the virus disrupts normal photosynthesis and nutrient transport, the plants struggle to store adequate reserves.

Marketability of the crop is severely compromised by the internal corking of the roots. Such tubers are unattractive to consumers and often fail to meet quality standards for fresh markets.

Infected plants exhibit reduced tolerance to abiotic stressors, such as drought, and are generally more susceptible to subsequent attacks by secondary pathogens, including soil-borne fungi.

Yield losses can vary significantly depending on the cultivar's susceptibility and the timing of the infection. Early-season infections generally cause the most severe economic losses.

The cumulative effect of viral infections over years makes continuous cultivation without the introduction of virus-indexed stock impossible, forcing farmers to bear high costs for planting material renewal.

The most effective management strategy is the use of certified virus-free planting material. Growers should source material produced via meristem-tip culture to ensure the absence of SPFMV.

Implementing a strict integrated pest management (IPM) program to control aphid populations is essential to reduce the rate of virus transmission within the field.

Rogueing, or the removal and destruction of symptomatic plants, helps to limit the amount of inoculum available for vectors to spread throughout the remainder of the crop.

Maintaining a clean field environment by removing weeds and ensuring spatial separation from old sweet potato plantings reduces the risk of virus introduction.

Regular field scouting and monitoring for both symptoms and vector presence allow for timely decision-making regarding protective measures and crop management.