Fungal Pathogen Behind Banana Wipeout Identified

The fungal pathogen Fusarium oxysporum f.sp. cubense (Foc) tropical race 4 (TR4) is the source of the disease Fusarium wilt of banana (FWB), which is threatening to functionally wipe out the bananas in the supermarket.

However, it is now known 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 appears to be triggered by some accessory genes associated with nitric oxide production. This knowledge results from recent research conducted by an international team of scientists led by the University of Massachusetts Amherst.

The findings, published in Nature Microbiology, pave the way for treatments and strategies that might reduce if not completely stop, the uncontrolled spread of Foc TR4.

The kind of banana we eat today is not the same as the one your grandparents ate. Those old ones, the Gros Michel bananas, are functionally extinct, victims of the first Fusarium outbreak in the 1950s.”

Li-Jun Ma, Study Senior Author and Professor, Department of Biochemistry and Molecular Biology, University of Massachusetts Amherst

Today, the Cavendish variety is the most common commercially accessible banana. It was developed as a disease-resistant response to the Gros Michel extinction. For approximately 40 years, the Cavendish banana thrived in the massive monoculture plantations that provide most of the world’s commercial banana production.

However, the Cavendish banana’s prosperous years had faded by the 1990s.

There was another outbreak of banana wilt. It spread like wildfire from South-East Asia to Africa and Central America.”

Yong Zhang, Ph.D., Study Lead Author, Organismic and Evolutionary Biology Program, University of Massachusetts Amherst

Ma added, “We have spent the last 10 years studying this new outbreak of banana wilt.”

Ma specializes in Fusarium oxysporum, a “species complex” consisting of hundreds of variants that target distinct plant hosts rather than being a single species. In addition to a common core genome, these variations are defined by the acquisition of accessory genes unique to each strain.

Ma further added, “We now know that the Cavendish banana-destroying pathogen TR4 did not evolve from the race that decimated the Gros Michel bananas. TR4’s genome contains some accessory genes that are linked to the production of nitric oxide, which seems to be the key factor in TR4’s virulence.”

Yong, Ma, and their co-authors from South Africa, China, and American universities sequenced and analyzed 36 distinct Foc strains gathered from all around the world, including strains that damage Gros Michel bananas, to reach this result.

With the support of UMass Amherst’s Institute for Applied Life Sciences, the scientists then determined that Foc TR4, which is responsible for the current outbreak of banana wilt, employs several auxiliary genes to produce and detoxify fungal nitric oxide to infect the host.

While the researchers do not know how these activities lead to disease infestation in Cavendish bananas, they discovered that eliminating two genes that govern nitric oxide synthesis significantly lowered the pathogenicity of Foc TR4.

Yong added, “Identifying these accessory genetic sequences opens up many strategic avenues to mitigate, or even control, the spread of Foc TR4.”

Nonetheless, Ma is quick to point out that the fundamental issue with one of the favorite breakfast foods is the practice of monocropping.

Ma concluded, “When there’s no diversity in a huge commercial crop, it becomes an easy target for pathogens. Next time you’re shopping for bananas, try some different varieties that might be available in your local specialty foods store.”