New banana disease is spreading fast and poses a threat to Africa's food security

Current measures to stop the spread of the disease are not effective

A new banana fungus is spreading rapidly across the world and now also in Africa, genetic research by Utrecht University (UU) and Wageningen University & Research (WUR) shows. PhD candidate Anouk van Westerhoven and colleagues warn that the disease threatens food security in Africa. 

The research shows that Tropical Race 4 (TR4), a variant of Fusarium wilt, is on the rise in Mozambique. This variant spread from Asia to South America and Africa over the past decade. The first reports of the disease came out of Mozambique in 2013, after which things remained quiet for years. "The disease seemed to be under control in Africa. However, we have since learned that this is, sadly, not the case," says Wageningen Professor of Phytopathology Gert Kema, who supervised Van Westerhoven's research together with Utrecht-based bioinformatician and data scientist Michael Seidl

Van Westerhoven and Seidl analysed the genetic material of the fungus from samples of diseased banana plants that were collected in Mozambique by a local researcher. By doing so, they showed that the TR4 fungus made it to at least 200 kilometers from the original plantation. The genetic research shows that the fungi found in different locations are closely related, which indicates that the pathogen found in Mozambique has a single origin.

Banana plants showing symptoms of Fusarium wilt

Spread through Africa

“That first source of infection was not under control after all,” says Van Westerhoven. “The disease continues to spread, including among small-scale farmers and people with banana plants in their gardens. They probably do not recognise the disease and, as a result, are unable to adequately treat it.”

“The question is not if, but rather when, the disease will spread to other African countries,” she states. In countries such as Tanzania, Malawi, Uganda and Ruanda, bananas are a staple food for millions of people. They often grow the Cavendish banana that is sold in supermarkets all over the world, but often also local banana strains. ”For many of these strains it is not known whether or not they are susceptible to TR4. That means that this disease is a threat to food security in these countries,” Kema warns.

New strain, old disease

Kema’s expectation is based on past experiences. The Fusarium fungus is well-known within the world of banana growers. In the twenties, thirties and forties of the last century, Panama disease wreaked havoc throughout Latin America. This disease was caused by other Fusarium fungi, and its destruction was finally halted when farmers started growing the resistant Cavendish banana.

The Cavendish banana currently dominates the world market. TR4 is a new Fusarium variant that affects this and many other banana varieties. And even though it has been almost ten years since TR4 first appeared in Mozambique, it is still largely unknown which African banana varieties are susceptible to TR4.

Transferred by humans, cars and water

With the same type of banana growing on large plantations everywhere, the disease spreads rapidly. “It is a soil-borne fungus,” Kema explains. “Floods help the spread enormously. Moreover, the fungus may be transferred through contaminated tools, soil carried on shoes and car tyres. There is abundant traffic on plantations, and the bananas are picked by hand.” Van Westerhoven adds: "It is very difficult to contain the disease. Despite the measures, the disease still rears its head in all regions where bananas are produced."

Growing alternative varieties

According to Van Westerhoven, speed and openness are needed to contain the spread of a disease such as Fusarium. Unfortunately, both are lacking: "It was, for example, very difficult to get Fusarium samples out of Mozambique, while it clearly is important to monitor the spread of TR4 there."

Kema points out that it is very important to know which types of banana are susceptible and which are not. "As soon as TR4 shows up somewhere else, it must be known which varieties can still be grown," Kema said. "The ultimate solution lies in new, resistant varieties. That requires breeding, which is a time-consuming process." Several projects to create new banana varieties have now been started in Wageningen.

Concerns over African food security

Eventually, other bananas will be sold on the European markets, according to Kema. “But my biggest concern is not whether western consumers will be able to eat bananas in the future. This is about food security in Africa. This is what we are worried about, now that this fungus spreads so easily.”

Publication

Dissemination of Fusarium wilt of banana in Mozambique caused by Fusarium odoratissimum Tropical Race 4

Anouk C. van Westerhoven, Harold Meijer, Joost Houdijk, Einar Martínez de la Parte, Elie Luntadila Matabuana, Michael Seidl, and Gerrit H.J. Kema

Plant Disease, 19 August 2022, https://doi.org/10.1094/PDIS-07-22-1576-SC