The bananas in your grocery store and that you eat for breakfast are in danger of functional extinction due to the disease Fusarium banana wilt (FWB), caused by a fungal pathogen called Fusarium oxysporum f.sp. cuboidal (Focus)tropical race 4 (TR4). However, 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 wiped out commercial banana production in the 1950s and that the virulence of this new strain appears to be caused by a number of additional genes involved in nitric oxide production. The research, published in Natural microbiology, opens the door to treatments and strategies that will stop the previously uncontrolled spread of Focus TR4.
“The kind of banana we eat today is not the same one your grandparents ate. Those old ones, the Gros Michel bananas, are functionally extinct, victims of the first Fusarium outbreak in the 1950s,” said Li-Jun Ma, professor of biochemistry and molecular biology at UMass Amherst and senior author of the paper.
Today, the most popular type of commercially available banana is the Cavendish variety, which was breaded as a disease-resistant response to the Gros Michel extinction. For about forty years, the Cavendish banana thrived around the world on the vast monoculture plantations that supply most of the world’s commercial banana crop.
But by the 1990s, the good times for the Cavendish banana began to end. “There was another outbreak of banana wilt,” said lead author Yong Zhang, who completed his doctorate under Ma’s supervision in UMass Amherst’s Organismic and Evolutionary Biology program. “It spread like wildfire from Southeast Asia to Africa and Central America.”
“We have been studying this new outbreak of banana wilt for the past decade,” said Ma, an expert in the field Fusarium oxysporumwhich is not a single species, but a ‘species complex’ with hundreds of different varieties that specialize in affecting different plant hosts. These varieties are defined by the acquisition of strain-specific accessory genes in addition to a shared core genome. “We now know that the Cavendish banana-destroying pathogen TR4 did not evolve from the variety that decimated Gros Michel bananas. The genome of TR4 contains some additional genes related to nitric oxide production, which appears to be the key factor in the development of TR4.” virulence.”
To reach this conclusion, Yong, Ma and their co-authors from China and South Africa, as well as universities in the US, examined 36 different Focus species collected from around the world, including those that attack Gros Michel bananas. Then the team discovered that, with the help of UMass Amherst’s Institute for Applied Life Sciences Focus TR4, responsible for the current banana wilt outbreak, uses several additional genes for both the production and detoxification of nitric oxide from the fungus to enter the host.
Although the team does not yet know exactly how these activities contribute to disease contamination in Cavendish bananas, they were able to determine that the virulence of Focus TR4 was greatly reduced when two genes that control nitric oxide production were eliminated.
‘Identifying these additional genetic sequences opens many strategic avenues to limit or even control the spread of this disease Focus TR4,” says Yong.
Yet Ma is quick to point out that the ultimate problem facing one of our favorite breakfast foods is the practice of monoculture. “If there is no diversity in a huge commercial crop, it becomes an easy target for pathogens,” she says. “The next time you go to buy bananas, try some different varieties that may be available at your local specialty store.”
Funding for this research was provided by 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.
