The IAEA’s successful field trial

Fusarium wilt caused by the fungus Fusarium oxysporum poses a major threat to banana cultivation worldwide. The pathogen is detrimental to bananas. As banana cultivation plays a crucial role in global food security, addressing this challenge is imperative. In a noteworthy development, the IAEA has completed a field trial with promising results, marking a critical step forward in the fight against this devastating disease.

Bananas are among the most produced, traded and consumed fruits globally. With over 1000 varieties, they provide vital nutrients to populations in producing and importing countries. The most traded variety is the Cavendish banana, which accounts for just under half of global production and has an estimated annual production volume of 50 million tonnes. Bananas are of particular significance in some of the least developed countries and in low-income food-deficit countries where, as a cash crop, they contribute not only to household food security but to income generation.

The threat of Fusarium wilt

Fusarium wilt is not a new problem. The Gros Michel banana variety, which once dominated the global market, was decimated by the disease in the mid-twentieth century. In response, the Cavendish variety, which was resistant to the original strain of Fusarium wilt, was developed. However, the pathogen has evolved and the new tropical race 4 (TR4) — the latest variant of the fungus Fusarium oxysporum — now threatens the Cavendish variety.

Pooja Mathur, a leading researcher at the Joint FAO/IAEA Centre of Nuclear Techniques in Food and Agriculture (Joint FAO/IAEA Centre), explains the seriousness of the situation: “The spread of TR4 is currently confirmed in 21 banana-producing countries and could have devastating effects on banana production and, consequently, on food security.”

Once a piece of farmland becomes contaminated with TR4, managing the disease is challenging and costly in all reported cases. This highlights the urgency of developing resistant banana varieties to safeguard the industry.

While Cavendish is widely known as a ‘table banana’ consumed as a dessert or fruit, many other banana varieties are staple foods, particularly in developing countries. These ‘cooking bananas’ are integral to the everyday diet of millions of people. For example, the Mchare banana, an East African diploid variety, is a popular cooking banana favoured in Tanzania and Uganda. These cooking bananas are also at risk of Fusarium wilt, posing a serious threat to food security in these regions.

A promising breakthrough

The IAEA, in collaboration with the International Institute of Tropical Agriculture, recently completed an 18-month field trial that has yielded highly promising results. Conducted in a region of Tanzania known to be a Fusarium oxysporum f.sp. cubense (Foc) race 1 pathogen hotspot and with high prevalence of the disease, the trial tested Mchare type cooking bananas, which were developed through the nuclear technique of mutation breeding.

“For us, the primary objective is to generate Fusarium wilt disease-resistant bananas in Africa, which are vital for food security and income generation for millions. This research is crucial because the disease poses a significant threat to banana crops, especially in regions where bananas are a staple food and a major source of income,” said Altus Viljoen, an expert on Fusarium wilt from Stellenbosch University. Mchare is one of the parents of Cavendish and improving its genetics hold tremendous potential for banana improvement.

Research and innovation at the Joint FAO/IAEA Centre

For several decades, the Joint FAO/IAEA Centre has been at the forefront of combating Fusarium wilt. It has developed tools and technologies for mutation breeding with the aim of enhance banana resistance. Initially focused on race 1 of Fusarium wilt, research has now expanded to address TR4. The field trial involved planting the 3000 individual Mchare banana mutant varieties in a Tanzanian hotspot with a high incidence of Fusarium wilt (Foc1). By continuously introducing the Fusarium fungus to the field, the IAEA ensured that disease pressure remained consistently high. To accurately assess resistance, the mutant lines were planted alongside wild-type controls and susceptible varieties.

After 18 months, the trial results were clear: a significant proportion of Mchare bananas showed complete resistance to Fusarium wilt, while the susceptible controls were severely affected.

“This research is critical for both food security and the future of banana cultivation,” says Pooja Mathur. “Improving the resistance of parental lines like Mchare is a significant step towards developing robust Cavendish bananas capable of withstanding TR4.”

The next phase involves further evaluation of the resistant lines in multi-location hotspot regions for Foc1 as well as Foc, tropical race 4 (Foc TR4), in Mozambique. These steps will ensure the durability and effectiveness of the resistant lines in a range of environmental conditions.

The path ahead

The successful field trial marks a significant breakthrough in the fight against Fusarium wilt. By focusing on parental improvement through mutation breeding, the Joint FAO/IAEA Centre is developing a sustainable and durable solution to the Fusarium wilt threat to help safeguard banana cultivation across the globe.