The bananas you see in your fruit bowl might be facing a serious threat of extinction. A widely consumed variety of bananas is under attack from a fungal disease known as Fusarium wilt of banana (FWB), which disrupts nutrient flow, causing the fruit to wilt. This devastating pathogen led to the near-extinction of the Gros Michel banana species in the 1950s.
However, there's hope on the horizon. A team of international scientists has recently identified the molecular mechanisms behind this destructive microbe, paving the way for new treatment strategies to combat the pathogen. Their groundbreaking research was published on August 16 in *Nature Microbiology*.
What’s Endangering Bananas?
The crisis stems from a fungal pathogen with a daunting name: Fusarium oxysporum f.sp. Cubense (Foc) tropical race 4 (TR4), commonly referred to as Foc TR4. This fungus not only caused widespread destruction of banana crops in the 1950s but also eradicated an entire banana species. Unfortunately, bananas aren’t the only plants susceptible to this pathogen.
“Fusarium oxysporum, as a species complex, can infect over 100 different plant hosts,” explains Li-Jun Ma, a molecular biologist at the University of Massachusetts Amherst and co-author of the study published in *Popular Science*.
The fungus’s virulence is partly due to its adaptable genome. Each Fusarium oxysporum genome consists of two components: a core genome responsible for essential functions and an accessory genome that varies among strains and enables the pathogen to target specific plants.
Understanding the pathogen’s genomic structure is crucial for developing methods to protect banana species from future extinction.
A New Era of Banana and Fungus Battles
In the mid-20th century, the Gros Michel banana was the first casualty of this fungal threat. In response, the Cavendish variety was developed as a disease-resistant alternative and remains the most popular banana variety today. However, by the 1990s, banana wilt re-emerged, spreading from Southeast Asia to Central America.
For the past decade, Ma and her team have been unraveling the genetic secrets of TR4 to tackle the latest outbreak. Surprisingly, they discovered that TR4 is not a descendant of the pathogen that wiped out Gros Michel bananas.
“We now know that the Cavendish banana-destroying pathogen TR4 did not evolve from the race that decimated the Gros Michel bananas,” Ma noted in a press release. “TR4’s genome includes accessory genes associated with nitric oxide production, a key factor in its virulence.”
The Role of Nitric Oxide in Pathogen Invasion
In their study, Ma’s team, including researchers from the United States, China, and South Africa, sequenced and compared 36 Foc strains globally. The analysis revealed that Foc TR4, responsible for the current banana wilt outbreak, uses accessory genes for producing and detoxifying nitric oxide during host invasion.
“As expected, we identified accessory sequences in the TR4 genome contributing to its virulence, particularly the production of nitric oxide, which aids in host invasion,” says Ma.
While the exact role of nitric oxide in causing disease in Cavendish bananas remains unclear, the team found that eliminating the two genes controlling its production significantly reduced TR4’s virulence.
“Identifying these genetic sequences offers new strategies to mitigate or even control the spread of Foc TR4,” says Yong Zhang, a postdoctoral researcher at UMASS Amherst and study co-author.
Future Directions and Lessons for Agriculture
Future research aims to uncover how the fungus produces nitric oxide without harming itself and to explore methods to disrupt its production. The team also plans to investigate genes that could neutralize the gas before it damages plant cells.
This research underscores the dangers of monocropping—relying on a single crop variety in agriculture—which creates an ideal environment for pathogens to thrive.
“To reduce the risks, consumers can support diverse banana varieties and local producers by purchasing different types of bananas,” Ma suggests.
Moreover, this situation highlights the importance of appreciating the efforts of those who grow our food.
“Bananas and other fruits or vegetables don’t just appear in grocery stores. There’s a tremendous amount of work behind the food on our tables. So, always remember to thank a farmer when you meet one,” Ma advises.