African cassava mosaic

The hallmark symptom is a mosaic pattern on the leaves, manifesting as an irregular interspersion of bright yellow, pale green, and dark green patches.

Leaf blades often show significant distortion, becoming crinkled, curled, or reduced in size, which drastically limits the plant's photosynthetic capacity.

A marked stunting is observed across the entire plant: stems become slender and internodes shorten, giving the plant a dwarfed and sickly appearance.

In severe infections, chlorotic areas may become necrotic, leading to premature leaf drop and the exposure of weakened branches.

Symptoms are most prominent on young, developing leaves, while older leaves may exhibit milder or less obvious signs of the viral infection.

The causative agent of this disease is a group of viruses belonging to the genus Begomovirus, most notably the African cassava mosaic virus (ACMV) within the family Geminiviridae.

These viruses contain a single-stranded DNA genome and primarily infect members of the Euphorbiaceae family, causing severe issues for cassava (Manihot esculenta).

The viral particles exhibit a characteristic twinned (geminate) structure, which provides them with environmental stability and high efficiency in hijacking plant cell machinery.

The infection spreads systemically through the plant's vascular tissue, effectively disrupting nutrient transport and metabolic processes.

The pathogen is transmitted both through the use of infected vegetative cuttings and by the whitefly vector Bemisia tabaci.

The development and spread of the disease are highly dependent on the population of the whitefly vector Bemisia tabaci, which thrives in warm and humid tropical climates.

Temperatures between 25–30 degrees Celsius are optimal for the rapid reproduction of the insect vector and the swift replication of the virus within host tissues.

The use of infected planting material is the primary driver for the long-distance dissemination of the virus to new plantations.

Poor crop rotation practices and the lack of phytosanitary quarantine measures create ideal conditions for the sustained buildup of the pathogen reservoir.

Nearby weeds that serve as alternate hosts for the virus or the vector significantly increase the risk of field-level infection.

The economic impact of African cassava mosaic is severe, as it causes a significant reduction in tuber yield, often resulting in losses of 50–90%.

Because the plant's energy production is compromised, tubers remain underdeveloped, fibrous, and of poor quality for consumption or processing.

Infected plants exhibit reduced resistance to secondary pathogens and abiotic stress, which often leads to the total loss of the crop stand.

The need for complete removal of infected plants and the procurement of healthy replacements imposes a heavy financial burden on farming communities.

Widespread outbreaks of this disease pose a direct threat to food security in regions where cassava is a dietary staple.

The most effective strategy for disease management is the use of virus-free planting material, often propagated through meristem culture in specialized laboratories.

Implementing breeding programs for resistant or tolerant cassava varieties is a critical long-term goal for sustainable crop production.

Strict phytosanitary practices must be enforced, including the immediate rogueing and burning of symptomatic plants to reduce the local inoculum source.

Integrated pest management targeting the whitefly vector is essential, utilizing both chemical insecticides and cultural practices to discourage vector colonization.

• Establishing spatial isolation between new and old cassava plantings.
• Monitoring fields regularly for early detection of symptoms.
• Clearing surrounding weed host reservoirs before the planting season.