Outsmarting bacterial wilt in Africa:
Tomato and pepper breeders declare war on persistent pathogen

– 15 January 2026 –

As climate change increases crop disease pressure across Africa, tomato and pepper scientists have launched the largest-ever coordinated research effort to combat bacterial wilt. The highly aggressive disease causes substantial losses for tomato and pepper growers and is expected to worsen as rising temperatures and heavier rainfall favor its spread.

Tomatoes and peppers are among Africa’s most important horticultural crops, central to daily diets, local markets and smallholder incomes – making the impact of the disease particularly severe.

Now, a four-year project, led by WorldVeg as part of the Africa Vegetable Breeding Consortium (AVBC), aims to identify tomato and pepper lines that can withstand the soil-borne pathogen, which can cause crop failure worth millions of dollars each year.

It will test a range of tomato and pepper lines across multiple farming environments from Benin in the West to Tanzania in the East, to identify sources of resistance in tomato and tolerance in pepper. It will also characterize the pathogen, analyzing its diversity, aggressiveness and adaptation to different environments. The results will guide crop breeding efforts to develop improved tomato and pepper varieties for Africa.

“Bacterial wilt is a particularly unfair disease. It strikes after farmers have already invested heavily in their crop, often just as flowering begins”, said Mwasilwa Ambali, lead technology scaling specialist at WorldVeg, based in Benin, who coordinates  the AVBC . “Once symptoms appear, there is no curative solution, the crop is lost. The only effective way to manage bacterial wilt is through the use of resistant varieties”. This closes down options for farmers to produce some of the most highly demanded and profitable vegetable crops in the continent.

“That stops here.”

High stakes for food systems and livelihoods

Across much of Africa, tomatoes and peppers are grown, traded and consumed at scale. Produced in both smallholders and peri-urban commercial farms, they are staple ingredients in daily cooking and important cash crops, particularly for women.

But bacterial wilt – caused by Ralstonia solanacearum, a group of closely related soil-borne bacteria – is their nemesis, infecting plants through their roots and blocking water transport. Affected plants can collapse rapidly, even when growing conditions appear favourable. In severe outbreaks farmers can face devastating yield losses, and once established, the pathogen can persist in the soil for years. Chemical treatments are ineffective, and crop rotation offers limited protection.

Researchers believe the disease is likely to become more severe in Africa as temperatures rise and rainfall patterns change. It thrives in warm, moist conditions, and climate change is expected to increase those conditions across many growing regions through higher temperatures, heavier rainfall and flooding.

In tomatoes, the research will evaluate breeding lines containing different combinations of known resistance markers, known as BW12 and BW6. These are associated with improved tolerance to bacterial wilt, but their effectiveness varies by location. By testing these combinations side by side across diverse conditions, researchers aim to identify tomato lines with broad and durable tolerance, rather than resistance that breaks down after a few seasons.

Chili peppers present a bigger challenge. There are currently no known major resistance genes for bacterial wilt in chilli. However, earlier screening has identified chili lines that perform better under disease pressure, suggesting the presence of quantitative tolerance – a plant’s ability to limit disease damage through the combined effect of multiple genes. Testing these lines across multiple environments will help identify material suitable for future breeding.

Partner-funded research model

The project will be funded through partner participation, with seed companies contributing fees in return for early access to research findings and breeding material, providing them with a competitive edge in tomato and pepper varieties resistant to bacterial wilt. Participation in the project is only open to AVBC members. Register to join AVBC.

AVBC is a joint initiative of WorldVeg and the African Seed Trade Association (AFSTA), which aims to promote the development of a strong vegetable seed sector in Africa. It connects vegetable breeders, entomologists, pathologists and other researchers with seed companies and farmers, and provides members with breeding lines of improved tomato, pepper, okra, amaranth, mungbean, African eggplant, and pumpkin.

This work contributes to the WorldVeg Action Area on Climate Resilience as part of the Center’s new WorldVeg Global Strategy 2026-2033.