Banana production in Mozambique and the rest of Africa could be jeopardized by the spread of the Fusarium oxysporum (TR4) fungus, which has caused significant losses in other producing countries.

Cavendish banana plantations in Mozambique, where the disease was first recorded on two commercial banana farms in 2013, have shown the most severe external symptoms, caused by TR4. "Formal confirmation was only published in 2020," say the scientists in their article published in the journal Plant Disease on May 8.

The team of researchers led by Anouk van Westerhoven from Wageningen University & Research and Utrecht University confirmed the presence of TR4 beyond the boundaries of the farms with the initial infestations, indicating its uncontrolled spread in Mozambique.

This alarming result demonstrates the failure of previous management methods. The uncontrolled spread of the disease therefore calls for immediate action to protect banana production and subsequently the livelihoods of millions of people in Africa.

"The spread of the disease to other farms in the country strongly suggests that TR4 has not been successfully contained. This underlines the failure of the management strategies implemented, which threatens food security in East Africa," they add.

It is suspected that human factors, such as increased international travel or environmental and climate change, have probably driven the emergence, evolution and spread of pathogens to new geographical regions or ecological niches.

"Often, new incursions go unnoticed and, since fungal pathogens are endemic, successful management of the disease is basically unfeasible, as exemplified by the very few examples of successful eradication. These cases often depend on fungicides and the complete eradication of host plants, which illustrates the importance of an accurate understanding of the host range of a pathogen," said the scientists.

They noted that effective and open science on a local and global scale is crucial to enable a rapid and coordinated response to emerging and invasive fungal diseases such as these.

"TR4 continues to spread regardless of the strategies implemented, and we observe that new incursions often do not lead to effective and transparent responses and data sharing, which are necessary to improve disease control. The recently reported uncontrolled spread of FWB in Mozambique poses a serious threat to African food security and global banana production.

Now, almost 10 years after its introduction in Africa, we call for radical TR4 eradication strategies, together with proactive resistance screening of African banana germplasm and intensified breeding programs for this important staple crop," they said.

The FAO warned that no banana variety available on the market is resistant to TR4 and, consequently, surveillance and management of the disease are currently the only strategies to control its spread.

To prepare Southern African Development Community (SADC) member countries against the possible incursion of Foc TR4, the FAO organized training to help raise awareness of Foc TR4 in Africa and identify the strains of Foc collected in the region. Efforts were also made to develop guidelines and provide training on the prevention and management of the disease.

World trade in bananas has skyrocketed in recent years, with an estimated export volume of 21 million metric tons in 2019, according to the FAO.

Outbreaks of the disease were vital in playing an important role in the defection and transition of the "Gros Michel" to the Cavendish subgroup in the trade. Today, both for export and for production on small farms, the above banana cultivars are the most widely grown throughout the world.

Van Westerhoven and colleagues collected fungal samples from 13 symptomatic banana trees found in northern Mozambique and tested the samples using molecular diagnostics and greenhouse pathogenicity assays. The samples tested positive for TR4, which led the researchers to investigate genetic variation and the potential origin of TR4 in Mozambique.

Based on the small amount of genetic variation revealed in this research, the researchers speculate that TR4 is spreading in reproduction.

Corresponding authors Gert Kema and Michael Seidl explained: "It is likely that the cultivation of Cavendish bananas - a banana variety that stopped the previous epidemic affecting Gros Michel bananas in the 1950s - is now a vehicle for worldwide spread, since global banana cultivation is dominated by the highly susceptible Cavendish clones. In addition, there is a lot of trafficking in the banana world. Mobile work crews, international labor contracting, and many of these workers and their managers are unaware of the danger of fungal diseases."

Despite this information, there are still gaps in knowledge that prevent successful containment of the little aggressive fungus. "Unfortunately, we don't have access to data on farms, which is essential for monitoring the disease," say Kema and Seidl.

The dire situation requires more action, research and transparent data sharing to implement new management strategies - such as the generation and release of genetically diverse and resistant germplasm for growers in Africa - which will hopefully reduce the ramifications of this complex fungal disease.

The highly virulent disease Fusarium wilt of banana (FWB), popularly known as Panama disease, has spread in the last 10 years from Southeast Asia, where it was isolated for almost 20 years, to other parts of the world, including Africa. It is the first banana disease to spread worldwide in the first half of the 20th century.

The disease affects almost all banana varieties, including the globally exported Cavendish (common banana) and local varieties from the East African highlands - crucial cash crops and staple foods for millions of people in the region.

A previous survey was carried out over two seasons in banana-based subsistence farming systems in Rwanda, Burundi, northwestern Tanzania (Kagera and Kigoma regions) and eastern Democratic Republic of Congo (South Kivu province) to investigate the distribution and incidence of banana FWB as a function of farming systems, soil and climatic factors and socioeconomics. The incidence of FWB was found to be generally high in the region, as 54.1% of all farms had an incidence of the disease higher than 40%, with Tanzania having the highest incidence (63.6%).

For the first time, the occurrence of FWB in Rwanda and Burundi suggests that strategies for its management in East and Central Africa should include raising farmers' awareness of the pathogen's spreading mechanisms and improving their access to disease-free planting materials.

This study showed that the incidence of the disease was lower on farms growing mixed cultivars and at higher altitudes (above 1,600 m above sea level). In addition, a significant association was observed between FWB and the age of the farm, with the incidence of the disease being higher on farms aged between 10 and 30 years.

Local varieties are essential for food security in the Great Lakes Region, where bananas are one of the main staple crops that already suffer from many other pests and diseases, such as nematodes, weevils, Xanthomonas bacterial wilt and black leaf streak disease, also known as Black Sigatoka.

The region is said to have one of the highest per capita banana consumptions in the world, from 400 to 600 kg.

Incursions of the TR4 disease, which is spreading globally from its Asian center and in 1876 in Australia, where it was first identified, to other banana-producing regions, have been recorded in most of the main banana-growing regions.

In West Africa, the Caribbean and Tropical America, the disease has spread rapidly.

Symptoms include yellowing, stunting and death of seedlings and yellowing and stunting of older plants. Infected plants wilt quickly, the lower leaves turn yellow and dry, the xylem tissues turn brown and the plant may die. In the early stages of the disease, the roots are not rotten.