Banana apocalypse: Can science save our favorite fruit?

The humble banana, a staple of many healthy diets, is on the brink of extinction due to Fusarium wilt of banana (FWB). This is a devastating disease caused by a strain of the fungal pathogen Fusarium oxysporum f.sp. cubense (Foc) Tropical Race 4 (TR4).

Thanks to an international team of scientists led by the University of Massachusetts Amherst, we now know that Foc TR4 did not evolve from the strain that wiped out commercial banana crops in the 1950s.

Instead, the virulence of this new strain seems to be associated with certain accessory genes linked to the production of nitric oxide.

These insights could pave the way for treatments and strategies that can slow, if not control, the unchecked spread of Foc TR4.

A tale of two bananas

“The kind of banana we eat today is not the same as the one your grandparents ate. Those old ones, the Gros Michel bananas, are functionally extinct, victims of the first Fusarium outbreak in the 1950s,” noted Li-Jun Ma, professor of biochemistry and molecular biology at UMass Amherst and the paper’s senior author.

Today, the most popular type of commercially available banana is the Cavendish variety, which was bred as a disease-resistant response to the Gros Michel extinction.

For about four decades, the Cavendish banana thrived across the globe in the vast monocultured plantations that supply the majority of the world’s commercial banana crop.

Banana disease and its impact

By the 1990s, the glory days of the Cavendish banana were slowly fading with another outbreak of banana wilt. This outbreak rapidly spread from Southeast Asia to Africa and Central America.

“There was another outbreak of banana wilt,” said lead author Yong Zhang, who completed his doctorate in UMass Amherst’s Organismic and Evolutionary Biology program under Ma’s direction. “It spread like wildfire from Southeast Asia to Africa and Central America.”

“We have spent the last 10 years studying this new outbreak of banana wilt,” noted Ma, who is an expert in Fusarium oxysporum, which is not a single species but a “species complex” with hundreds of different varieties that specialize in affecting different plant hosts.

These varieties are determined by the acquisition of strain-specific accessory genes in addition to a shared core genome.

“We now know that the Cavendish banana-destroying pathogen TR4 did not evolve from the race that decimated the Gros Michel bananas,” said Ma.

“TR4’s genome contains some accessory genes that are linked to the production of nitric oxide, which seems to be the key factor in TR4’s virulence.”

Strategies to mitigate banana disease

Yong, Ma, and their co-authors from China, South Africa, and various U.S. universities rigorously sequenced and compared 36 different Foc strains from around the globe.

The team discovered that Foc TR4 uses some accessory genes for both the production and detoxification of fungal nitric oxide to invade the host.

This key discovery revealed the immense impact of nitric oxide production on TR4’s virulence, thus offering several strategic pathways to control the spread of this pathogen.

While the team doesn’t yet know exactly how these activities contribute to disease infestation in Cavendish bananas, they were able to determine that the virulence of Foc TR4 was greatly reduced when two genes that control nitric oxide production were eliminated.

“Identifying these accessory genetic sequences opens up many strategic avenues to mitigate, or even control, the spread of Foc TR4,” said Yong.

Diversifying the bananas we buy

Even so, Ma is quick to point out that the ultimate problem threatening our much-loved breakfast fruit is the practice of monocropping.

“When there’s no diversity in a huge commercial crop, it becomes an easy target for pathogens,” she said. “Next time you’re shopping for bananas, try some different varieties that might be available in your local specialty foods store.”

Diversifying the types of bananas we consume could help reduce the pressure on the Cavendish variety, making the entire banana industry more resilient.

Supporting biodiversity in banana crops is not just about preserving a favorite fruit; it’s about ensuring food security for future generations.

The study is published in the journal Nature Microbiology.

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