The bananas you buy at the grocery store and enjoy for breakfast are threatened by a serious issue known as Fusarium wilt of banana (FWB), which is caused by a fungus called Fusarium oxysporum f.sp. cubense (Foc) tropical race 4 (TR4). However, new findings from a global team of researchers indicate that this harmful strain did not originate from the variety that devastated commercial banana crops in the 1950s. The new strain’s increased virulence appears to be linked to certain accessory genes related to nitric oxide production. This research paves the way for potential treatments and methods to manage, or even halt, the currently uncontrolled spread of Foc TR4.
The bananas in your supermarket and that you eat for breakfast are facing functional extinction due to the disease Fusarium wilt of banana (FWB) caused by a fungal pathogen called Fusarium oxysporum f.sp. cubense (Foc) tropical race 4 (TR4). However, thanks to recent research from 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 and that the virulence of this new strain seems to be caused by some accessory genes that are associated with the production of nitric oxide. The research, published in Nature Microbiology, opens the door to treatments and strategies that can slow, if not control, the as-of-yet unchecked spread of Foc TR4.
According to Li-Jun Ma, a professor of biochemistry and molecular biology at UMass Amherst and lead author of the study, “The type of banana we consume today is different from what your grandparents had. The older variety, known as Gros Michel bananas, has become nearly extinct due to the first Fusarium outbreak in the 1950s.”
Currently, the most widely sold banana variety is the Cavendish, which was cultivated to resist the disease that wiped out Gros Michel. For about four decades, the Cavendish banana flourished in the extensive monoculture plantations that supply most of the world’s commercial bananas.
However, by the late 1990s, the fortunes of the Cavendish banana began to decline. “There was another outbreak of banana wilt,” says Yong Zhang, the study’s lead author and PhD graduate of UMass Amherst’s Organismic and Evolutionary Biology program. “It spread rapidly from Southeast Asia to Africa and Central America.”
“Our team has spent the last decade investigating this new banana wilt outbreak,” notes Ma, an authority on Fusarium oxysporum, a ‘species complex’ consisting of many strains that target various plants. These strains are shaped by specific accessory genes along with a common core genome. “We’ve established that the pathogen TR4, which threatens Cavendish bananas, is not a descendant of the race that caused the decline of Gros Michel bananas. The genome of TR4 contains accessory genes tied to nitric oxide production, a crucial factor regarding its aggressiveness.”
To reach this conclusion, Yong, Ma, and other collaborators from China, South Africa, and other U.S. universities analyzed and compared 36 different Foc strains collected globally, including those that affect Gros Michel bananas. Using resources from UMass Amherst’s Institute for Applied Life Sciences, the team found that Foc TR4, responsible for the ongoing banana wilt crisis, uses certain accessory genes to produce and detoxify fungal nitric oxide, enabling it to invade its host.
While the exact impact of these functions on disease progression in the Cavendish variety remains unclear, they determined that the virulence of Foc TR4 significantly decreased when two genes controlling nitric oxide production were removed.
“Recognizing these accessory genetic elements opens up various potential approaches to mitigate or even tackle the spread of Foc TR4,” explains Yong.
Nevertheless, Ma emphasizes that the core issue threatening one of our favorite breakfast items is the practice of monocropping. “Uniformity in large commercial crops makes them susceptible to disease,” she explains. “Next time you buy bananas, consider trying different varieties that may be available at specialty food stores in your area.”
This research was funded by multiple organizations, including the U.S. National Science Foundation, the U.S. Department of Agriculture’s National Institute of Food and Agriculture, the U.S. Department of Health and Human Services, the U.S. Department of Energy, the National Institutes of Health, the Guangdong Science and Technology Project, CARS, and the Laboratory of Lingnan Modern Agriculture Project.
