Viral epidemics in legumes raise alarm over food security in Africa

The study warns that Africa’s major legume viruses can spread internationally through seed movement and vector transport. Strengthening quarantine systems is therefore essential to prevent global dissemination, particularly for virus complexes like groundnut rosette that have not yet reached other continents.

A new scientific review warns that virus diseases are causing widespread damage to Africa’s most important food legumes, undermining food security and threatening the livelihoods of millions of smallholder farmers across the continent. The comprehensive analysis highlights six viral disease groups that are inflicting severe yield losses on staple legumes such as cowpea, common bean, chickpea, faba bean, groundnut and soybean, crops that form the backbone of Africa’s nutrition and agricultural economy.

The peer-reviewed article, “Virus Diseases of Economic Importance on Food Legumes in Africa and Their Control” and published in Viruses, delivers one of the most extensive examinations to date of the viruses affecting African legume crops. The study compiles decades of regional research and recent survey data to outline the distribution, characteristics, transmission mechanisms and available control strategies for viruses now considered among the continent’s most economically damaging plant pathogens.

The findings present a continent-wide picture of escalating viral threats. They reveal that many African nations are experiencing crop losses linked to viruses that spread rapidly through aphid vectors, seed transmission, mixed infections and poor awareness at the farm level. Despite substantial knowledge about the viruses themselves, the study warns that adoption of available control techniques remains far too limited to produce large-scale impact.

Viral threats escalating across Africa’s six most important legume crops

The review identifies six major viral disease complexes that consistently cause serious economic losses in African agriculture. Each affects a different legume crop, and all are widespread across entire regional farming systems.

1. Common Bean Mosaic and Black Root Disease

Common bean, widely grown and consumed throughout sub-Saharan Africa, is suffering high yield losses due to infections by Bean common mosaic virus (BCMV) and Bean common mosaic necrosis virus (BCMNV). These viruses infect beans grown nearly everywhere on the continent and can reduce yields by up to 80 percent in susceptible cultivars.

BCMV and BCMNV are transmitted by aphids and through infected seeds. BCMNV is especially destructive because it triggers a lethal necrosis syndrome, known as black root, in varieties carrying the I resistance gene. The study notes that although genetically resistant varieties exist, adoption remains inconsistent, and clean seed systems, essential for breaking the seed-transmission cycle, are poorly established.

2. Cowpea Mosaic Disease

Cowpea, the most widely cultivated indigenous legume in Africa, is highly vulnerable to mosaic disease caused by viruses such as Cowpea aphid-borne mosaic virus (CABMV), BCMV-BlCM, and Cucumber mosaic virus (CMV). These viruses are responsible for widespread mosaic, mottling and stunting symptoms that can lead to complete crop failure.

Mixed infections create even more severe losses, sometimes killing plants outright. The review stresses that seed transmission and aphid-mediated spread make these viruses particularly hard to control. While resistance genes have been identified in cowpea breeding lines, the paper notes that farmers rarely have access to certified virus-free seeds, resulting in recurring outbreaks.

3. Chickpea Stunt Disease

Chickpea production across eastern and northern Africa is increasingly threatened by stunt disease caused by two major poleroviruses: Chickpea chlorotic stunt virus (CpCSV) and Beet western yellows virus (BWYV). These viruses can cause up to 95 percent yield loss in severe epidemics, wiping out entire fields.

The review explains that CpCSV is now widespread in Northeast Africa, North Africa and West Asia, while BWYV has an even broader host range and global distribution. The disease produces severe stunting, leaf discoloration and poor or absent pod formation. No resistant chickpea varieties are commercially available, although recent research in Tunisia and Syria has identified promising tolerant genotypes. Until resistance becomes available, the study recommends interim integrated management using vector control, improved planting dates and seed treatment.

4. Faba Bean Necrotic Yellows and Stunt Disease

Faba bean is widely grown in Ethiopia, Egypt, Sudan, Algeria and Morocco, but yields are heavily reduced by two closely related nanoviruses: Faba bean necrotic yellows virus (FBNYV) and Faba bean necrotic stunt virus (FBNSV). These viruses cause some of the most destructive legume disease outbreaks ever recorded on the continent.

Major epidemics in Egypt in the 1990s resulted in yield losses of 70 to 90 percent. Similar devastating outbreaks have occurred in Ethiopia. The nanoviruses are transmitted persistently by aphids and can kill faba bean plants within weeks of infection. Because natural resistance has not been identified in thousands of screened genotypes, faba bean viral disease management currently depends on cultural controls and strategic insecticide applications. The study calls for long-term exploration of genetic engineering and genome-editing technologies to introduce resistance.

5. Groundnut Rosette Disease

Groundnut rosette disease (GRD), which affects peanuts, is described as the most destructive legume viral disease in Africa. Caused by the interaction of Groundnut rosette virus, Groundnut rosette assistor virus and a satellite RNA, GRD leads to stunting, leaf distortion and complete crop failure when plants are infected early.

The paper recounts catastrophic epidemics, including a 1975 outbreak in northern Nigeria that destroyed an estimated 0.7 million hectares of groundnut worth hundreds of millions of dollars. Because GRD is confined to Africa, the disease represents a major regional threat with no global precedent. Resistant varieties remain the most sustainable control method, but adoption remains uneven across rural regions.

6. Soybean Mosaic Diseases

Soybean production in Africa, although expanding rapidly, faces growing risk from three viruses: Soybean mosaic virus (SMV), Cowpea mild mottle virus (CPMMV), and Soybean blotchy mosaic virus (SbBMV). While SMV has historically been considered less economically significant in Africa, the study warns that CPMMV is emerging as a major threat in West Africa, causing severe mosaic, bud blight, necrosis and significant yield declines.

SBMV, first identified in South Africa, also contributes to losses through mosaic symptoms and seed quality reduction. Despite these risks, research on soybean viruses in Africa remains limited, leaving major knowledge gaps across many soybean-growing countries.

Nearly all major viruses spread through Aphids and seed, but adoption of controls lags

The review notes that aphids transmit most of these viruses either persistently or non-persistently, making vector control an essential part of disease management. However, smallholder farmers in sub-Saharan Africa often lack the resources needed for effective insecticide use.

Seed transmission also drives repeated outbreaks, especially for potyviruses infecting bean, cowpea and soybean. The study emphasizes that clean seed systems are urgently needed to limit initial inoculum, but most countries lack structured virus-free seed production programs.

Resistance breeding has shown success in several crops, notably beans, cowpea and groundnut, but progress is uneven. In many regions, farmers continue planting susceptible varieties due to limited access to improved seeds, insufficient extension services and economic constraints.

The study stresses that integrated virus management yields the best results. Effective strategies combine:

• Resistant varieties
• Cultural practices such as optimal planting dates and rogueing
• Vector management
• Clean seed production and distribution
• Continuous monitoring and early detection

Yet, adoption remains sporadic. Wide gaps exist between available scientific guidance and what farmers implement on the ground. Economic limitations, weak extension systems and lack of awareness hinder progress, resulting in sustained virus pressure across Africa.

Strengthened surveillance, diagnostic capacity and farmer adoption

The review provides urgent recommendations to strengthen Africa’s response to legume virus threats. It highlights the need for continent-wide virus surveys, explaining that many African legume-growing countries still have no documented virus reports, not because viruses are absent, but because surveys have never been conducted.

Modern diagnostic tools such as PCR, RT-PCR, ELISA and next-generation sequencing are essential for accurate virus identification, yet access remains limited in many national programs. Strengthening diagnostic capacity is crucial for detecting emerging strains, tracking virus evolution and guiding resistance breeding.

The author stresses the need for:

• Large-scale surveillance to map virus incidence and economic impact
• Epidemiological research to track vector dynamics and infection pathways
• Breeding programs targeting durable resistance
• Public sector investment in clean seed systems
• Farmer education to boost adoption of control strategies
• Regional information exchange to harmonize management approaches

The study warns that Africa’s major legume viruses can spread internationally through seed movement and vector transport. Strengthening quarantine systems is therefore essential to prevent global dissemination, particularly for virus complexes like groundnut rosette that have not yet reached other continents.