Gaby
Bad news for banana lovers: bananas may soon disappear from supermarket shelves. The culprit is a disease called Fusarium wilt of banana (FWB), which blocks the flow of nutrients to the fruit and makes the plant wilt. The 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 argues that a similar pathogen wiped out several commercial banana crops in the 1950s, driving the Gros Michel variety to functional extinction. The team’s research has uncovered molecular mechanisms behind the pathogen, opening the door to new treatment methods and strategies to fight Foc TR4.
A Key Milestone: Studying the Genome
“This pathogen can infect over 100 different plant species,” Li-Jun Ma, a molecular biologist and co-author of the study, told Popular Science. She said the disease is now decimating Cavendish bananas, the most popular and widely available bananas in the world. Once the fungus gets into a banana field, it is nearly impossible to eradicate, making the future of Cavendish production look bleak. The team investigated the genome of Fusarium oxysporum and how it changes. Ma explained that the genome can be divided into two parts: the core and the accessory. The core genome contains genes for essential survival functions, while the accessory genome varies from strain to strain and can carry specialized functions, including infecting particular plants. Understanding how the pathogen and its genome work at the molecular level is crucial for developing ways to combat it and prevent the loss of more banana varieties.
What Researchers Discovered
Cavendish was developed in response to the collapse of Gros Michel. For several decades, Cavendish proved to be a desirable and disease-resistant variety. But in the 1990s a new outbreak of banana wilt emerged and spread from Southeast Asia to Central America. Over the past decade, Ma’s team has been studying the TR4 genome in the context of the outbreak affecting Cavendish bananas. They found that the current outbreak is caused by a different strain than the one that devastated crops in the 1950s. Ma said the TR4 genome contains accessory genes linked to the production of nitric oxide, which appears to be a key factor in TR4’s virulence.
A Mysterious and Harmful Gas
In the study, Ma and her co-authors from institutions in the U.S., China, and South Africa sequenced and compared 36 different Foc strains from around the world, including those that destroyed Gros Michel bananas. The analysis showed that Foc TR4, which is responsible for the current outbreak, uses some accessory genes to both 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,” Ma said. The team still does not know exactly how this gas helps the fungus infect Cavendish bananas. However, they found that TR4’s virulence drops significantly when two genes that control nitric oxide production are removed. In future work, the team plans to investigate how the fungus makes such a harmful gas without poisoning itself.
The team also pointed out that widespread cultivation of a single crop variety, a practice known as monoculture farming, creates a favorable environment for pathogens to evolve. They suggested intentionally choosing different banana varieties on store shelves to boost demand for diversity. The results of their work were published in the journal Nature Microbiology.
