US research pinpoints genes behind devastating crop disease hindering global banana production

19 Aug 2024 --- Bananas are at risk of functional extinction due to Fusarium wilt of banana (FWB) disease, commonly known as Panama disease, which is caused by a fungal pathogen. However, new research from the University of Massachusetts Amherst, US, has detected some “accessory genes” within the fungus that produce nitric oxide and contribute to wilting.

Today’s most popular type of banana is the Cavendish variety, bred in response to Gros Michel bananas going extinct in the 1950s. The Cavendish bananas have been around since then, grown widely in monoculture plantations that meet most of the world’s commercial demands for the fruit.

“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,” says Li-Jun Ma, biochemistry and molecular biology professor at UMass Amherst and the paper’s senior author.

However, an outbreak of banana wilt hit the Cavendish variety in the 1990s. “It spread like wildfire from Southeast Asia to Africa and Central America,” notes lead author Yong Zhang of the school’s Organismic and Evolutionary Biology program.

“We have spent the last ten years studying this new outbreak of banana wilt,” says Ma, an expert in the fungal pathogen Fusarium oxysporum f.sp. cubense (Foc) tropical race 4 (TR4), responsible for Panama disease. The fungus has hundreds of varieties affecting various plant hosts.

The findings

The researchers have concluded that the pathogen TR4, which destroyed the Cavendish banana, did not evolve from the race that decimated the Gros Michel bananas. “TR4’s genome contains some accessory genes linked to the production of nitric oxide, which seems to be the key factor in TR4’s virulence,” adds Ma.

Yong, Ma and other researchers from China, South Africa and US universities compared 36 strains of the fungus worldwide, including strains that wiped out Gros Michel bananas.

The team found that Foc TR4, associated with the current cases of banana disease, uses accessory genes to produce and detoxify fungal nitric oxide to attack the host.

While more research is required to understand how this phenomenon leads to disease infestation in bananas, the team showed that the severity of the Foc TR4 significantly reduced when two genes that steer nitric oxide production were removed.

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

Despite the breakthrough, Ma maintains that the single biggest problem endangering bananas is monocropping, the agricultural practice of growing the same crop on the same piece of land year after year.

“When there’s no diversity in a huge commercial crop, it becomes an easy target for pathogens,” she says.

“Next time you’re shopping for bananas, try different varieties in your local specialty foods store.”