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

Cavendish (common banana) banana plantations in Mozambique, where the disease was first recorded on two commercial banana farms in 2013, have been showing the most severe external symptoms caused by TR4. "Formal confirmation was not published until 2020," the scientists say in their paper 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 farm boundaries with 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 requires 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 geographic regions or ecological niches.

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

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 note that new incursions often do not lead to effective and transparent responses and data sharing, which are needed 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 into Africa, we call for radical strategies to eradicate TR4, along with proactive screening of resistance in African banana germplasm and intensification of 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, FAO organized training to help raise awareness of Foc TR4 in Africa and identify Foc strains 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 soared 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 a major role in the defection and transition of the 'Gros Michel' to the Cavendish subgroup in trade. Today, both in export and small farm production, the above banana cultivars are the most widely grown worldwide.

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, prompting the researchers to investigate the genetic variation and potential origin of TR4 in Mozambique.

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

Corresponding authors Gert Kema and Michael Seidl explained, "It is likely that growing 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 the global banana crop 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 hires, and many of these workers and their managers are unaware of the danger of fungal diseases."

Despite this information, there are still knowledge gaps that prevent successful containment of the unaggressive fungus. "Unfortunately, we do not have access to farm data, 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 to growers in Africa - that 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 nearly 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 East African highland varieties - crucial cash crops and staple foods for millions of people in the region.

A previous survey was conducted 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 cropping systems, soil and climate factors and socio-economics. 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 greater 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 mechanisms of pathogen spread 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 farm age, with the incidence of the disease being highest on farms aged between 10 and 30 years.

Local varieties are essential for food security in the Great Lakes Region, where banana is a major staple crop that already suffers 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 consumption in the world, at 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 major banana producing 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 rapidly, lower leaves turn yellow and dry, xylem tissues turn brown, and the plant may die. In the early stages of the disease, roots are not rotted.