Sad news for banana lovers: they may soon disappear from supermarket shelves. The culprit is a disease known as Fusarium wilt of banana (FWB), which blocks the flow of nutrients to the fruit, causing it to wilt. This disease is caused by a fungal pathogen with a long name: Fusarium oxysporum f.sp. cubense (Foc) tropical race 4 (TR4), or simply Foc TR4. An international team of scientists led by the University of Massachusetts Amherst has suggested that this pathogen wiped out several commercial banana crops in the 1950s, leading to the functional extinction of the Gros Michel banana variety. The team’s research has uncovered the molecular mechanisms behind the pathogen that kills bananas, opening the door to new treatment methods and strategies to combat Foc TR4.
A Key Milestone: Studying the Genome
“This pathogen can infect over 100 different plant species,” said Li-Jun Ma, a molecular biologist and co-author of the study, in an interview with Popular Science. According to her, the disease is currently decimating Cavendish bananas, the most popular and widely available bananas in the world. Once the fungus enters a banana field, it becomes nearly impossible to eradicate, making the future of Cavendish banana production look bleak. The scientists decided to thoroughly investigate the genome of Fusarium oxysporum and how it changes. Ms. Ma explained that this genome can be divided into two parts: the core and the accessory. The core genome performs all the essential functions for survival, while the accessory genome can vary freely from strain to strain and carry out specialized functions, including infecting specific plants. Understanding how the pathogen and its genome operate at the molecular level is crucial for developing ways to combat it and prevent the extinction of more banana varieties.
What Researchers Discovered
Thus, the development of the Cavendish variety was once a response to the extinction of the Gros Michel bananas. For several decades, Cavendish established itself as a sought-after and disease-resistant variety. However, in the 1990s, another outbreak of banana wilt emerged, spreading from Southeast Asia to Central America. Over the past decade, Ms. Ma’s team has been studying the TR4 genome in the context of the new outbreak affecting Cavendish bananas. They found that the cause of the outbreak is not the same strain that devastated crops in the 1950s. “The TR4 genome contains some accessory genes associated with the production of nitric oxide, which appears to be a key factor in TR4’s virulence,” the scientists suggested.
A Mysterious and Harmful Gas
In their work, Ms. Ma and her co-authors from research institutions in the U.S., China, and South Africa sequenced and compared 36 different strains of Foc from around the world, including those that destroyed Gros Michel bananas. The analysis revealed that Foc TR4, responsible for the current banana wilt outbreak, utilizes some accessory genes to produce and detoxify fungal nitric oxide. “We found accessory sequences in the TR4 genome that contribute to its virulence, including the production of the harmful gas nitric oxide, which facilitates invasion of the host,” Ms. Ma stated. Her team still does not know how this gas aids in infecting Cavendish bananas. However, they have determined that the virulence of Foc TR4 significantly decreases when two genes controlling nitric oxide production are removed. In their future research, the team aims to better understand how the fungus can produce such a harmful gas without harming itself.
The researchers also noted that the widespread cultivation of a single crop variety, known as monoculture farming, creates a nurturing environment for the development of pathogens. “To increase demand for diverse bananas in the market, it’s worth intentionally choosing different varieties on the shelves each time,” the scientists advised. The results of their work were published in the journal Nature Microbiology.