The end of the banana is nigh, but biologists may have found the key to their survival.

The bananas in your supermarket that you eat for breakfast are facing functional extinction due to Fusarium wilt of banana (FWB), which is caused by a fungus called Fusarium oxysporum f.sp. cubense (Foc) Tropical Race 4 (TR4).

But thanks to recent research by 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 decimated commercial banana crops in the 1950s, and that the virulence of this new strain appears to be driven by some accessory genes involved in nitric oxide production.

Search, Published in Natural microbiologyThis discovery opens the door to treatments and strategies that can slow, if not control, the spread of Foc TR4, which has so far been uncontrolled.

“The banana we eat today is not the same as the one our ancestors ate,” says Li Jun Ma, a professor of biochemistry and molecular biology at the University of Massachusetts Amherst and lead author of the study. “Those ancient bananas, the Gros Michel, are functionally extinct, having been the victim of the first Fusarium outbreak in the 1950s.”

Today, the most popular commercially available banana is the Cavendish, which was bred as a disease-resistant response after the extinction of the Gros Michel. For about 40 years, the Cavendish banana has thrived around the world in vast monoculture plantations that provide the majority of the world’s commercial banana crop.

But by the 1990s, the good times for Cavendish bananas were coming to an end. “Banana wilt struck again,” says lead author Yong Zhang, who completed his doctorate in the UMass Amherst program in organismal and evolutionary biology under Ma’s supervision. “It spread like wildfire from Southeast Asia to Africa and Central America.”

“We have spent the last 10 years studying this new banana wilt epidemic,” says Ma, an expert on Fusarium oxporum, which is not a single species but a “species group” of hundreds of different species that specialize in infecting different plant hosts. These species are defined by the acquisition of additional strain-specific genes in addition to a common core genome.

“We now know that the TR4 pathogen that destroys Cavendish bananas did not evolve from the strain that destroyed Gros Michel bananas. The TR4 genome contains some additional genes related to nitric oxide production, which appears to be the key factor in TR4’s virulence.”

To reach this conclusion, Young, Ma, and colleagues from China, South Africa, and universities in the United States sequenced and compared 36 different Foc strains collected from around the world, including those that attack Gros Michel bananas. Then, with the help of the UMass Amherst Institute for Applied Life Sciences, the team discovered that Foc TR4, the strain responsible for the current banana wilt outbreak, uses certain helper genes to produce and detoxify fungal nitric oxide toxins to invade the host.

While the team does not yet know exactly how these activities contribute to disease in Cavendish bananas, they were able to determine that the virulence of Foc TR4 was significantly reduced when two genes that control nitric oxide production were knocked out.

“Identifying these additional genetic sequences opens up many strategic avenues to mitigate or even control the spread of Foc TR4,” Young says.

However, Ma is quick to point out that the ultimate problem facing one of our favorite breakfast foods is the practice of monoculture.

“When there is no diversity in a large commercial crop, it becomes an easy target for pathogens,” she says. “The next time you are shopping for bananas, try some of the different varieties that may be available at your local specialty food store.”